The Project Gutenberg eBook of The Birth-Time of the World and Other Scientific Essays

This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online at www.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.

Title: The Birth-Time of the World and Other Scientific Essays

Author: John Joly

Release date: August 28, 2005 [eBook #16614]

Most recently updated: December 12, 2020

Language: English

Credits: Produced by Hugh Rance

*** START OF THE PROJECT GUTENBERG EBOOK THE BIRTH-TIME OF THE WORLD AND OTHER SCIENTIFIC ESSAYS ***

THE BIRTH-TIME OF THE WORLD AND OTHER SCIENTIFIC ESSAYS

by

J. JOLY, M.A., Sc.D., F.R.S.,

PROFESSOR OF GEOLOGY AND MINERALOGY IN THE UNIVERSITY OF DUBLIN

E. P. DUTTON AND COMPANY

681 FIFTH AVENUE NEW YORK

Produced by Hugh Rance, 2005

Cover

Title page

CONTENTS PAGE

I. THE BIRTH-TIME OF THE WORLD - - - - - - - - - - - 1

II. DENUDATION  - - - - - - - - - - - - - - - - - - 30

III. THE ABUNDANCE OF LIFE  - - - - - - - - - - - - 60

IV. THE BRIGHT COLOURS OF ALPINE FLOWERS - - - - - 102

V. MOUNTAIN GENESIS  - - - - - - - - - - - - - - - 116

VI. ALPINE STRUCTURE - - - - - - - - - - - - - - - 146

VII. OTHER MINDS THAN OURS - - - - - - - - - - - - 162

VIII. THE LATENT IMAGE - - - - - - - - - - - - - - 202

IX. PLEOCHROIC HALOES  - - - - - - - - - - - - - - 214

X. THE USE OF RADIUM IN MEDICINE - - - - - - - - - 244

XI. SKATING  - - - - - - - - - - - - - - - - - - - 260

XII. A SPECULATION AS TO A PRE-MATERIAL UNIVERSE - 288

LIST OF ILLUSTRATIONS

PLATE I. LAKE OF LUCERNE, LOOKING WEST FROM BRUNNEN -

Frontispiece

PLATE II. "UPLIFTED FROM THE SEAS." CLIFFS OF THE TITLIS,

SWITZERLAND - to face p. 4

PLATE III. AN ALPINE TORRENT AT WORK—VAL D'HERENS, SWITZERLAND -

to face p. 31

PLATE IV. EARTH PILLARS—VAL D'HERENS - to face p. 34

PLATE V. "SCENES OF DESOLATION." THE WEISSHORN SEEN FROM BELLA

TOLA, SWITZERLAND - to face p. 40

PLATE VI. ALLUVIAL CONE—NICOLAI THAL, SWITZERLAND. MORAINE ON

ALETSCH GLACIER SWITZERLAND - to face p. 50

PLATE VII. IN THE REGION OF THE CROCI; DOLOMITES. THE ROTHWAND

SEEN FROM MONTE PIANO - to face p. 60

PLATE VIII. FIRS ASSAILING THE HEIGHTS OF THE MADERANER THAL,

SWITZERLAND - to face p. 73

PLATE IX. LIFE NEAR THE SNOW LINE; THE BOG-COTTON IN POSSESSION.

NEAR THE TSCHINGEL PASS, SWITZERLAND - to face p. 80

PLATE X. THE JOY OF LIFE. THE AMPEZZO THAL; DOLOMITES - to face

p. 93

PLATE XI. "PINES SOLEMNLY QUIET." DÜSSISTOCK; MADERANER THAL - to

face p. 100

PLATE XII. ALPINE FLOWERS IN THE VALLEYS - to face p. 105

PLATE XIII. ALPINE FLOWERS ON THE HEIGHTS - to face p. 106

PLATE XIV. MOUNTAIN SOLITUDES; VAL DE ZINAL. FROM LEFT TO RIGHT

ROTHHORN; BESSO; OBERGABELHORN; MATTERHORN; PIC DE ZINAL (THROUGH

CLOUD); DENT BLANCHE - to face p. 116

ix

PLATE XV. SECTOR OF THE EARTH RISE OF ISOGEOTHERMS INTO A DEPOSIT

EVOLVING RADIOACTIVE HEAT - to face p. 118

PLATE XVI. "THE MOUNTAINS COME AND GO." THE DENT BLANCHE SEEN

FROM THE SASSENEIRE - to face p. 133

PLATE XVII. DIAGRAMMATIC SECTIONS OF THE HIMALAYA - to face p.

140

PLATE XVIII. RESIDUES OF DENUDATION. THE MATTERHORN SEEN FROM THE

SUMMIT OF THE ZINAL ROTHHORN - to face p. 148

PLATE XIX. THE FOLDED ROCKS OF THE MATTERHORN, SEEN FROM NEAR

HÖHBALM. SKETCH MADE IN 1906 - to face p. 156

PLATE XX. SCHIAPARELLI'S MAP OF MARS OF 1882, AND ADDITIONS (IN

RED) OF 1892 - to face p. 166

PLATE XXI. GLOBE OF MARS SHOWING PATH OF IN-FALLING SATELLITE -

to face p. 188

PLATE XXII. CANALS MAPPED BY LOWELL COMPARED WITH CANALS FORMED

BY IN-FALLING SATELLITES - to face p. 192

PLATE XXIII. HALOES IN MICA; CO. CARLOW. HALO IN BIOTITE

CONTAINED IN GRANITE - to face p. 224

PLATE XXIV. RADIUM HALO, MUCH ENLARGED. THORIUM HALO AND RADIUM

HALO IN MICA - to face p. 228

PLATE XXV. HALO ROUND CAPILLARY IN GLASS TUBE. HALOES ROUND

TUBULAR PASSAGES IN MICA - to face p. 230

PLATE XXVI. ALETSCH GLACIER, SWITZERLAND - to face p. 282

PLATE XXVII. THE MIDDLE ALETSCH GLACIER JOINING THE GREAT ALETSCH

GLACIER. GLACIERS OF THE LAUTERBRUNNEN THAL - to face p. 285

PLATE XXVIII. PERCHED BLOCK ON THE ALETSCH GLACIER. GRANITE

ERRATIC NEAR ROUNDWOOD, CO. WICKLOW; NOW BROKEN UP AND REMOVED -

to face p. 286

And Fifteen Illustrations in the Text.

x

PREFACE

Tins volume contains twelve essays written at various times

during recent years. Many of them are studies contributed to

Scientific Reviews or delivered as popular lectures. Some are

expositions of views the scientific basis of which may be

regarded as established. Others—the greater number—may be

described as attempting the solution of problems which cannot be

approached by direct observation.

The essay on The Birth-time of the World is based on a lecture

delivered before the Royal Dublin Society. The subject has

attracted much attention within recent years. The age of the

Earth is, indeed, of primary importance in our conception of the

longevity of planetary systems. The essay deals with the

evidence, derived from the investigation of purely terrestrial

phenomena, as to the period which has elapsed since the ocean

condensed upon the Earth's surface. Dr. Decker's recent addition

to the subject appeared too late for inclusion in it. He finds

that the movements (termed isostatic) which geologists recognise

as taking place deep in the Earth's crust, indicate an age of the

same order of magnitude

xi

as that which is inferred from the statistics of denudative

history.[1]

The subject of _Denudation_ naturally arises from the first essay.

In thinking over the method of finding the age of the ocean by

the accumulation of sodium therein, I perceived so long ago as

1899, when my first paper was published, that this method

afforded a means of ascertaining the grand total of denudative

work effected on the Earth's surface since the beginning of

geological time; the resulting knowledge in no way involving any

assumption as to the duration of the period comprising the

denudative actions. This idea has been elaborated in various

publications since then, both by myself and by others.

"Denudation," while including a survey of the subject generally,

is mainly a popular account of this method and its results. It

closes with a reference to the fascinating problems presented by

the inner nature of sedimentation: a branch of science to which I

endeavoured to contribute some years ago.

_Mountain Genesis_ first brings in the subject of the geological

intervention of radioactivity. There can, I believe, be no doubt

as to the influence of transforming elements upon the

developments of the surface features of the Earth; and, if I am

right, this source of thermal energy is mainly responsible for

that local accumulation of wrinkling which we term mountain

chains. The

[1] Bull. Geol. Soc. America, vol. xxvi, March 1915.

xii

paper on _Alpine Structure_ is a reprint from "Radioactivity and

Geology," which for the sake of completeness is here included. It

is directed to the elucidation of a detail of mountain genesis: a

detail which enters into recent theories of Alpine development.

The weakness of the theory of the "horst" is manifest, however,

in many of its other applications; if not, indeed, in all.

The foregoing essays on the physical influences affecting the

surface features of the Earth are accompanied by one entitled _The

Abundance of Life._ This originated amidst the overwhelming

presentation of life which confronts us in the Swiss Alps. The

subject is sufficiently inspiring. Can no fundamental reason be

given for the urgency and aggressiveness of life? Vitality is an

ever-extending phenomenon. It is plain that the great principles

which have been enunciated in explanation of the origin of

species do not really touch the problem. In the essay—which is an

early one (1890)—the explanation of the whole great matter is

sought—and as I believe found—in the attitude of the organism

towards energy external to it; an attitude which results in its

evasion of the retardative and dissipatory effects which prevail

in lifeless dynamic systems of all kinds.

_Other Minds than Ours_? attempts a solution of the vexed question

of the origin of the Martian "canals." The essay is an abridgment

of two popular lectures on the subject. I had previously written

an account of my views which carried the enquiry as far as it was

in

xiii

my power to go. This paper appeared in the "Transactions of the

Royal Dublin Society, 1897." The theory put forward is a purely

physical one, and, if justified, the view that intelligent beings

exist in Mars derives no support from his visible surface

features; but is, in fact, confronted with fresh difficulties.

_Pleochroic Haloes_ is a popular exposition of an inconspicuous but

very beautiful phenomenon of the rocks. Minute darkened spheres—a

microscopic detail—appear everywhere in certain of the rock

minerals. What are they? The discoveries of recent radioactive

research—chiefly due to Rutherford—give the answer. The

measurements applied to the little objects render the explanation

beyond question. They turn out to be a quite extraordinary record

of radioactive energy; a record accumulated since remote

geological times, and assuring us, indirectly, of the stability

of the chemical elements in general since the beginning of the

world. This assurance is, without proof, often assumed in our

views on the geological history of the Globe.

Skating is a discourse, with a recent addition supporting the

original thesis. It is an illustration of a common experience—the

explanation of an unimportant action involving principles the

most influential considered as a part of Nature's resources.

The address on _The Latent Image_ deals with a subject which had

been approached by various writers before the time of my essay;

but, so far as I know, an explanation

xiv

based on the facts of photo-electricity had not been attempted.

Students of this subject will notice that the views expressed are

similar to those subsequently put forward by Lenard and Saeland

in explanation of phosphorescence. The whole matter is of more

practical importance than appears at first sight, for the

photoelectric nature of the effects involved in the radiative

treatment of many cruel diseases seems to be beyond doubt.

It was in connection with photo-electric science that I was led

to take an interest in the application of radioactivity in

medicine. The lecture on _The Use of Radium in Medicine_ deals with

this subject. Towards the conclusion of this essay reference will

be found to a practical outcome of such studies which, by

improving on the methods, and facilitating the application, of

radioactive treatment, has, in the hands of skilled medical men,

already resulted in the alleviation of suffering.

Leaving out much which might well appear in a prefatory notice, a

word should yet be added respecting the illustrations of scenery.

They are a small selection from a considerable number of

photographs taken during my summer wanderings in the Alps in

company with Henry H. Dixon. An exception is Plate X, which is by

the late Dr. Edward Stapleton. From what has been said above, it

will be gathered that these illustrations are fitly included

among pages which owe so much to Alpine inspiration. They

illustrate the

xv

subjects dealt with, and, it is to be hoped, they will in some

cases recall to the reader scenes which have in past times

influenced his thoughts in the same manner; scenes which in their

endless perspective seem to reduce to their proper insignificance

the lesser things of life.

My thanks are due to Mr. John Murray for kindly consenting to the

reissue of the essay on _The Birth-time of the World_ from the

pages of _Science Progress_; to Messrs. Constable & Co. for leave

to reprint _Pleochroic Haloes_ from _Bedrock_, and also to make some

extracts from _Radioactivity and Geology_; and to the Council of

the Royal Dublin Society for permission to republish certain

papers from the Proceedings of the Society.

_Iveagh Geological Laboratory, Trinity College, Dublin._

July, 1915.

xvi

THE BIRTH-TIME OF THE WORLD [1]

LONG ago Lucretius wrote: "For lack of power to solve the

question troubles the mind with doubts, whether there was ever a

birth-time of the world and whether likewise there is to be any

end." "And if" (he says in answer) "there was no birth-time of

earth and heaven and they have been from everlasting, why before

the Theban war and the destruction of Troy have not other poets

as well sung other themes? Whither have so many deeds of men so

often passed away, why live they nowhere embodied in lasting

records of fame? The truth methinks is that the sum has but a

recent date, and the nature of the world is new and has but

lately had its commencement."[2]

Thus spake Lucretius nearly 2,000 years ago. Since then we have

attained another standpoint and found very different limitations.

To Lucretius the world commenced with man, and the answer he

would give to his questions was in accord with his philosophy: he

would date the birth-time of the world from the time when

[1] A lecture delivered before the Royal Dublin Society, February

6th, 1914. _Science Progress_, vol. ix., p. 37

[2] _De Rerum Natura_, translated by H. A. J. Munro (Cambridge,

1886).

1

poets first sang upon the earth. Modern Science has along with

the theory that the Earth dated its beginning with the advent of

man, swept utterly away this beautiful imagining. We can, indeed,

find no beginning of the world. We trace back events and come to

barriers which close our vista—barriers which, for all we know,

may for ever close it. They stand like the gates of ivory and of

horn; portals from which only dreams proceed; and Science cannot

as yet say of this or that dream if it proceeds from the gate of

horn or from that of ivory.

In short, of the Earth's origin we have no certain knowledge; nor

can we assign any date to it. Possibly its formation was an event

so gradual that the beginning was spread over immense periods. We

can only trace the history back to certain events which may with

considerable certainty be regarded as ushering in our geological

era.

Notwithstanding our limitations, the date of the birth-time of

our geological era is the most important date in Science. For in

taking into our minds the spacious history of the universe, the

world's age must play the part of time-unit upon which all our

conceptions depend. If we date the geological history of the

Earth by thousands of years, as did our forerunners, we must

shape our ideas of planetary time accordingly; and the duration

of our solar system, and of the heavens, becomes comparable with

that of the dynasties of ancient nations. If by millions of

years, the sun and stars are proportionately venerable. If by

hundreds or thousands of millions of

2

years the human mind must consent to correspondingly vast epochs

for the duration of material changes. The geological age plays

the same part in our views of the duration of the universe as the

Earth's orbital radius does in our views of the immensity of

space. Lucretius knew nothing of our time-unit: his unit was the

life of a man. So also he knew nothing of our space-unit, and he

marvels that so small a body as the sun can shed so much, heat

and light upon the Earth.

A study of the rocks shows us that the world was not always what

it now is and long has been. We live in an epoch of denudation.

The rains and frosts disintegrate the hills; and the rivers roll

to the sea the finely divided particles into which they have been

resolved; as well as the salts which have been leached from them.

The sediments collect near the coasts of the continents; the

dissolved matter mingles with the general ocean. The geologist

has measured and mapped these deposits and traced them back into

the past, layer by layer. He finds them ever the same;

sandstones, slates, limestones, etc. But one thing is not the

same. _Life_ grows ever less diversified in character as the

sediments are traced downwards. Mammals and birds, reptiles,

amphibians, fishes, die out successively in the past; and barren

sediments ultimately succeed, leaving the first beginnings of

life undecipherable. Beneath these barren sediments lie rocks

collectively differing in character from those above: mainly

volcanic or poured out from fissures in

3

the early crust of the Earth. Sediments are scarce among these

materials.[1]

There can be little doubt that in this underlying floor of

igneous and metamorphic rocks we have reached those surface

materials of the earth which existed before the long epoch of

sedimentation began, and before the seas came into being. They

formed the floor of a vaporised ocean upon which the waters

condensed here and there from the hot and heavy atmosphere. Such

were the probable conditions which preceded the birth-time of the

ocean and of our era of life and its evolution.

It is from this epoch we date our geological age. Our next

purpose is to consider how long ago, measured in years, that

birth-time was.

That the geological age of the Earth is very great appears from

what we have already reviewed. The sediments of the past are many

miles in collective thickness: yet the feeble silt of the rivers

built them all from base to summit. They have been uplifted from

the seas and piled into mountains by movements so slow that

during all the time man has been upon the Earth but little change

would have been visible. The mountains have again been worn down

into the ocean by denudation and again younger mountains built

out of their redeposited materials. The contemplation of such

vast events

[1] For a description of these early rocks, see especially the

monograph of Van Hise and Leith on the pre-Cambrian Geology of

North America (Bulletin 360, U.S. Geol. Survey).

4

prepares our minds to accept many scores of millions of years or

hundreds of millions of years, if such be yielded by our

calculations.

THE AGE AS INFERRED FROM THE THICKNESS OF THE SEDIMENTS

The earliest recognised method of arriving at an estimate of the

Earth's geological age is based upon the measurement of the

collective sediments of geological periods. The method has

undergone much revision from time to time. Let us briefly review

it on the latest data.

The method consists in measuring the depths of all the successive

sedimentary deposits where these are best developed. We go all

over the explored world, recognising the successive deposits by

their fossils and by their stratigraphical relations, measuring

their thickness and selecting as part of the data required those

beds which we believe to most completely represent each

formation. The total of these measurements would tell us the age

of the Earth if their tale was indeed complete, and if we knew

the average rate at which they have been deposited. We soon,

however, find difficulties in arriving at the quantities we

require. Thus it is not easy to measure the real thickness of a

deposit. It may be folded back upon itself, and so we may measure

it twice over. We may exaggerate its thickness by measuring it

not quite straight across the bedding or by unwittingly including

volcanic materials. On the other hand, there

5

may be deposits which are inaccessible to us; or, again, an

entire absence of deposits; either because not laid down in the

areas we examine, or, if laid down, again washed into the sea.

These sources of error in part neutralise one another. Some make

our resulting age too long, others make it out too short. But we

do not know if a balance of error does not still remain. Here,

however, is a table of deposits which summarises a great deal of

our knowledge of the thickness of the stratigraphical

accumulations. It is due to Sollas.[1]

Feet.

Recent and Pleistocene  - -    4,000

Pliocene                 - -   13,000

Miocene                  - -   14,000

Oligocene                - -     2,000

Eocene                   - -  20,000

63,000

Upper Cretaceous        - -   24,000

Lower Cretaceous        - -   20,000

Jurassic                 - -    8,000

Trias                    - -   7,000

69,000

Permian                  - -    2,000

Carboniferous           - -    29,000

Devonian                 - -   22,000

63,000

Silurian                 - -   15,000

Ordovician              - -   17,000

Cambrian                 - -   6,000

58,000

Algonkian—Keeweenawan   - -   50,000

Algonkian—Animikian     - -   14,000

Algonkian—Huronian      - -   18,000

82,000

Archæan                   - -   ?

Total                     - - 335,000 feet.

[1] Address to the Geol. Soc. of London, 1509.

6

In the next place we require to know the average rate at which

these rocks were laid down. This is really the weakest link in

the chain. The most diverse results have been arrived at, which

space does not permit us to consider. The value required is most

difficult to determine, for it is different for the different

classes of material, and varies from river to river according to

the conditions of discharge to the sea. We may probably take it

as between two and six inches in a century.

Now the total depth of the sediments as we see is about 335,000

feet (or 64 miles), and if we take the rate of collecting as

three inches in a hundred years we get the time for all to

collect as 134 millions of years. If the rate be four inches, the

time is soo millions of years, which is the figure Geikie

favoured, although his result was based on somewhat different

data. Sollas most recently finds 80 millions of years.[1]

THE AGE AS INFERRED FROM THE MASS OF THE SEDIMENTS

In the above method we obtain our result by the measurement of

the linear dimensions of the sediments. These measurements, as we

have seen, are difficult to arrive at. We may, however, proceed

by measurements of the mass of the sediments, and then the method

becomes more definite. The new method is pursued as follows:

[1] Geikie, _Text Book of Geology_ (Macmillan, 1903), vol. i., p.

73, _et seq._ Sollas, _loc. cit._ Joly, _Radioactivity and Geology_

(Constable, 1909), and Phil. Mag., Sept. 1911.

7

The total mass of the sediments formed since denudation began may

be ascertained with comparative accuracy by a study of the

chemical composition of the waters of the ocean. The salts in the

ocean are undoubtedly derived from the rocks; increasing age by

age as the latter are degraded from their original character

under the action of the weather, etc., and converted to the

sedimentary form. By comparing the average chemical composition

of these two classes of material—the primary or igneous rocks and

the sedimentary—it is easy to arrive at a knowledge of how much

of this or that constituent was given to the ocean by each ton of

primary rock which was denuded to the sedimentary form. This,

however, will not assist us to our object unless the ocean has

retained the salts shed into it. It has not generally done so. In

the case of every substance but one the ocean continually gives

up again more or less of the salts supplied to it by the rivers.

The one exception is the element sodium. The great solubility of

its salts has protected it from abstraction, and it has gone on

collecting during geological time, practically in its entirety.

This gives us the clue to the denudative history of the

Earth.[1]

The process is now simple. We estimate by chemical examination of

igneous and sedimentary rocks the amount of sodium which has been

supplied to the ocean per ton of sediment produced by denudation.

We also calculate

[1] _Trans. R.D.S._, May, 1899.

8

the amount of sodium contained in the ocean. We divide the one

into the other (stated, of course, in the same units of mass),

and the quotient gives us the number of tons of sediment. The

most recent estimate of the sediments made in this manner affords

56 x 10^16 tonnes.[1]

Now we are assured that all this sediment was transported by the

rivers to the sea during geological time. Thus it follows that,

if we can estimate the average annual rate of the river supply of

sediments to the ocean over the past, we can calculate the

required age. The land surface is at present largely covered with

the sedimentary rocks themselves. Sediment derived from these

rocks must be regarded as, for the most part, purely cyclical;

that is, circulating from the sea to the land and back again. It

does not go to increase the great body of detrital deposits. We

cannot, therefore, take the present river supply of sediment as

representing that obtaining over the long past. If the land was

all covered still with primary rocks we might do so. It has been

estimated that about 25 per cent. of the existing continental

area is covered with archæan and igneous rocks, the remainder

being sediments.[2] On this estimate we may find valuable

[1] Clarke, _A Preliminary Study of Chemical Denudation_

(Washington, 1910). My own estimate in 1899 (_loc. cit._) made as a

test of yet another method of finding the age, showed that the

sediments may be taken as sufficient to form a layer 1.1 mile

deep if spread uniformly over the continents; and would amount to

64 x 10^18 tons.

[2] Van Tillo, _Comptes Rendues_ (Paris), vol. cxiv., 1892.

9

major and minor limits to the geological age. If we take 25 per

cent. only of the present river supply of sediment, we evidently

fix a major limit to the age, for it is certain that over the

past there must have been on the average a faster supply. If we

take the entire river supply, on similar reasoning we have what

is undoubtedly a minor limit to the age.

The river supply of detrital sediment has not been very

extensively investigated, although the quantities involved may be

found with comparative ease and accuracy. The following table

embodies the results obtained for some of the leading rivers.[1]

Mean annual   Total annual   Ratio of

discharge in  sediment in    sediment

cubic feet    thousands      to water

per second.   of tons.       by weight.

Potomac -        20,160          5,557        1 : 3.575

Mississippi -   610,000       406,250        1 : 1,500

Rio Grande -      1,700          3,830        1 : 291

Uruguay -       150,000         14,782       1 : 10,000

Rhone -          65,850         36,000       1 : 1,775

Po -             62,200         67,000       1 : 900

Danube -        315,200        108,000       1 : 2,880

Nile -          113,000         54,000       1 : 2,050

Irrawaddy -     475,000       291,430        1 : 1,610

Mean -          201,468        109,650       1 : 2,731

We see that the ratio of the weight of water to the

[1] Russell, _River Development_ (John Murray, 1888).

10

weight of transported sediment in six out of the nine rivers does

not vary widely. The mean is 2,730 to 1. But this is not the

required average. The water-discharge of each river has to be

taken into account. If we ascribe to the ratio given for each

river the weight proper to the amount of water it discharges, the

proportion of weight of water to weight of sediment, for the

whole quantity of water involved, comes out as 2,520 to 1.

Now if this proportion holds for all the rivers of the

world—which collectively discharge about 27 x 1012 tonnes of

water per annum—the river-born detritus is 1.07 x 1010 tonnes. To

this an addition of 11 per cent. has to be made for silt pushed

along the river-bed.[1] On these figures the minor limit to the

age comes out as 47 millions of years, and the major limit as 188

millions. We are here going on rather deficient estimates, the

rivers involved representing only some 6 per cent. of the total

river supply of water to the ocean. But the result is probably

not very far out.

We may arrive at a probable age lying between the major and minor

limits. If, first, we take the arithmetic mean of these limits,

we get 117 millions of years. Now this is almost certainly

excessive, for we here assume that the rate of covering of the

primary rocks by sediments was uniform. It would not be so,

however, for the rate of supply of original sediment must have

been continually diminishing

[1] According to observations made on the Mississippi (Russell,

_loc. cit._).

11

during geological time, and hence we may assume that the rate of

advance of the sediments on the primary rocks has also been

diminishing. Now we may probably take, as a fair assumption, that

the sediment-covered area was at any instant increasing at a rate

proportionate to the rate of supply of sediment; that is, to the

area of primary rocks then exposed. On this assumption the age is

found to be 87 millions of years.

THE AGE BY THE SODIUM OF THE OCEAN

I have next to lay before you a quite different method. I have

already touched upon the chemistry of the ocean, and on the

remarkable fact that the sodium contained in it has been

preserved, practically, in its entirety from the beginning of

geological time.

That the sea is one of the most beautiful and magnificent sights

in Nature, all admit. But, I think, to those who know its story

its beauty and magnificence are ten-fold increased. Its saltness

it due to no magic mill. It is the dissolved rocks of the Earth

which give it at once its brine, its strength, and its buoyancy.

The rivers which we say flow with "fresh" water to the sea

nevertheless contain those traces of salt which, collected over

the long ages, occasion the saltness of the ocean. Each gallon of

river water contributes to the final result; and this has been

going on since the beginning of our era. The mighty total of the

rivers is 6,500 cubic miles of water in the year!

12

There is little doubt that the primeval ocean was in the

condition of a fresh-water lake. It can be shown that a primitive

and more rapid solution of the original crust of the Earth by the

slowly cooling ocean would have given rise to relatively small

salinity. The fact is, the quantity of salts in the ocean is

enormous. We are only now concerned with the sodium; but if we

could extract all the rock-salt (the chloride of sodium) from the

ocean we should have enough to cover the entire dry land of the

Earth to a depth of 400 feet. It is this gigantic quantity which

is going to enter into our estimate of the Earth's age. The

calculated mass of sodium contained in this rock-salt is 14,130

million million tonnes.

If now we can determine the rate at which the rivers supply

sodium to the ocean, we can determine the age.[1] As the result

of many thousands of river analyses, the total amount of sodium

annually discharged to the ocean

[1] _Trans. R.D.S._, 1899. A paper by Edmund Halley, the

astronomer, in the _Philosophical Transactions of the Royal

Society_ for 1715, contains a suggestion for finding the age of

the world by the following procedure. He proposes to make

observations on the saltness of the seas and ocean at intervals

of one or more centuries, and from the increment of saltness

arrive at their age. The measurements, as a matter of fact, are

impracticable. The salinity would only gain (if all remained in

solution) one millionth part in Too years; and, of course, the

continuous rejection of salts by the ocean would invalidate the

method. The last objection also invalidates the calculation by T.

Mellard Reade (_Proc. Liverpool Geol. Soc._, 1876) of a minor limit

to the age by the calcium sulphate in the ocean. Both papers were

quite unknown to me when working out my method. Halley's paper

was, I think, only brought to light in 1908.

13

by all the rivers of the world is found to be probably not far

from 175 million tonnes.[1] Dividing this into the mass of

oceanic sodium we get the age as 80.7 millions of years. Certain

corrections have to be applied to this figure which result in

raising it to a little over 90 millions of years. Sollas, as the

result of a careful review of the data, gets the age as between

80 and 150 millions of years. My own result[2] was between 80 and

90 millions of years; but I subsequently found that upon certain

extreme assumptions a maximum age might be arrived at of 105

millions of years.[3] Clarke regards the 80.7 millions of years

as certainly a maximum in the light of certain calculations by

Becker.[4]

The order of magnitude of these results cannot be shaken unless

on the assumption that there is something entirely misleading in

the existing rate of solvent denudation. On the strength of the

results of another and

[1] F. W. Clarke, _A Preliminary Study of Chemical Denudation_

(Smithsonian Miscellaneous Collections, 1910).

[2] _Loc. cit._

[3] "The Circulation of Salt and Geological Time" (Geol. Mag.,

1901, p. 350).

[4] Becker (loc. cit.), assuming that the exposed igneous and

archæan rocks alone are responsible for the supply of sodium to

the ocean, arrives at 74 millions of years as the geological age.

This matter was discussed by me formerly (Trans. R.D.S., 1899,

pp. 54 _et seq._). The assumption made is, I believe, inadmissible.

It is not supported by river analyses, or by the chemical

character of residual soils from sedimentary rocks. There may be

some convergence in the rate of solvent denudation, but—as I

think on the evidence—in our time unimportant.

14

entirely different method of approaching the question of the

Earth's age (which shall be presently referred to), it has been

contended that it is too low. It is even asserted that it is from

nine to fourteen times too low. We have then to consider whether

such an enormous error can enter into the method. The

measurements involved cannot be seriously impugned. Corrections

for possible errors applied to the quantities entering into this

method have been considered by various writers. My own original

corrections have been generally confirmed. I think the only point

left open for discussion is the principle of uniformitarianism

involved in this method and in the methods previously discussed.

In order to appreciate the force of the evidence for uniformity

in the geological history of the Earth, it is, of course,

necessary to possess some acquaintance with geological science.

Some of the most eminent geologists, among whom Lyell and

Geikie[1] may be mentioned, have upheld the doctrine of

uniformity. It must here suffice to dwell upon a few points

having special reference to the matter under discussion.

The mere extent of the land surface does not, within limits,

affect the question of the rate of denudation. This arises from

the fact that the rain supply is quite insufficient to denude the

whole existing land surface. About 30 per cent. of it does not,

in fact, drain to the

[1] See especially Geikie's Address to Sect. C., Brit. Assoc.

Rep., 1399.

15

ocean. If the continents become invaded by a great transgression

of the ocean, this "rainless" area diminishes: and the denuded

area advances inwards without diminution. If the ocean recedes

from the present strand lines, the "rainless" area advances

outwards, but, the rain supply being sensibly constant, no change

in the river supply of salts is to be expected.

Age-long submergence of the entire land, or of any very large

proportion of what now exists, is negatived by the continuous

sequence of vast areas of sediment in every geologic age from the

earliest times. Now sediment-receiving areas always are but a

small fraction of those exposed areas whence the sediments are

supplied.[1] Hence in the continuous records of the sediments we

have assurance of the continuous exposure of the continents above

the ocean surface. The doctrine of the permanency of the

continents has in its main features been accepted by the most

eminent authorities. As to the actual amount of land which was

exposed during past times to denudative effects, no data exist to

show it was very different from what is now exposed. It has been

estimated that the average area of the North American continent

over geologic time was about eight-tenths of its existing

area.[2] Restorations of other continents, so far as they have

been attempted, would not

[1] On the strength of the Mississippi measurements about 1 to 18

(Magee, _Am. Jour. of Sc._, 1892, p. 188).

[2] Schuchert, _Bull. Geol. Soc. Am._, vol. xx., 1910.

16

suggest any more serious divergency one way or the other.

That climate in the oceans and upon the land was throughout much

as it is now, the continuous chain of teeming life and the

sensitive temperature limits of protoplasmic existence are

sufficient evidence.[1] The influence at once of climate and of

elevation of the land may be appraised at their true value by the

ascertained facts of solvent denudation, as the following table

shows.

Tonnes removed in      Mean elevation.

solution per square    Metres.

mile per annum.

North America -         79                  700

South America -         50                  650

Europe -                100                  300

Asia -                   84                  950

Africa -                 44                  650

In this table the estimated number of tonnes of matter in

solution, which for every square mile of area the rivers convey

to the ocean in one year, is given in the first column. These

results are compiled by Clarke from a very large number of

analyses of river waters. The second column of the table gives

the mean heights in metres above sea level of the several

continents, as cited by Arrhenius.[2]

Of all the denudation results given in the table, those relating

to North America and to Europe are far the

[1] See also Poulton, Address to Sect. D., Brit. Assoc. Rep.,

1896.

[2] _Lehybuch dev Kosmischen Physik_, vol. i., p. 347.

17

most reliable. Indeed these may be described as highly reliable,

being founded on some thousands of analyses, many of which have

been systematically pursued through every season of the year.

These show that Europe with a mean altitude of less than half

that of North America sheds to the ocean 25 per cent. more salts.

A result which is to be expected when the more important factors

of solvent denudation are given intelligent consideration and we

discriminate between conditions favouring solvent and detrital

denudation respectively: conditions in many cases

antagonistic.[1] Hence if it is true, as has been stated, that we

now live in a period of exceptionally high continental elevation,

we must infer that the average supply of salts to the ocean by

the rivers of the world is less than over the long past, and

that, therefore, our estimate of the age of the Earth as already

given is excessive.

There is, however, one condition which will operate to unduly

diminish our estimate of geologic time, and it is a condition

which may possibly obtain at the present time. If the land is, on

the whole, now sinking relatively to the ocean level, the

denudation area tends, as we have seen, to move inwards. It will

thus encroach upon regions which have not for long periods

drained to the ocean. On such areas there is an accumulation of

soluble salts which the deficient rivers have not been able to

carry to the ocean. Thus the salt content of certain of

[1] See the essay on Denudation.

18

the rivers draining to the ocean will be influenced not only by

present denudative effects, but also by the stored results of

past effects. Certain rivers appear to reveal this unduly

increased salt supply those which flow through comparatively arid

areas. However, the flowoff of such tributaries is relatively

small and the final effects on the great rivers apparently

unimportant—a result which might have been anticipated when the

extremely slow rate of the land movements is taken into account.

The difficulty of effecting any reconciliation of the methods

already described and that now to be given increases the interest

both of the former and the latter.

THE AGE BY RADIOACTIVE TRANSFORMATIONS

Rutherford suggested in 1905 that as helium was continually being

evolved at a uniform rate by radioactive substances (in the form

of the alpha rays) a determination of the age of minerals

containing the radioactive elements might be made by measurements

of the amount of the stored helium and of the radioactive

elements giving rise to it, The parent radioactive substances

are—according to present knowledge—uranium and thorium. An

estimate of the amounts of these elements present enables the

rate of production of the helium to be calculated. Rutherford

shortly afterwards found by this method an age of 240 millions of

years for a radioactive mineral of presumably remote age. Strutt,

who carried

19

his measurements to a wonderful degree of refinement, found the

following ages for mineral substances originating in different

geological ages:

Oligocene -               8.4 millions of years.

Eocene -                 31    millions of years.

Lower Carboniferous -  150   millions of years.

Archæan -               750    millions of years.

Periods of time much less than, and very inconsistent with, these

were also found. The lower results are, however, easily explained

if we assume that the helium—which is a gas under prevailing

conditions—escapes in many cases slowly from the mineral.

Another product of radioactive origin is lead. The suggestion

that this substance might be made available to determine the age

of the Earth also originated with Rutherford. We are at least

assured that this element cannot escape by gaseous diffusion from

the minerals. Boltwood's results on the amount of lead contained

in minerals of various ages, taken in conjunction with the amount

of uranium or parent substance present, afforded ages rising to

1,640 millions of years for archæan and 1,200 millions for

Algonkian time. Becker, applying the same method, obtained

results rising to quite incredible periods: from 1,671 to 11,470

millions of years. Becker maintained that original lead rendered

the determinations indefinite. The more recent results of Mr. A.

Holmes support the conclusion that "original" lead may be present

and may completely falsify results derived

20

from minerals of low radioactivity in which the derived lead

would be small in amount. By rejecting such results as appeared

to be of this character, he arrives at 370 millions of years as

the age of the Devonian.

I must now describe a very recent method of estimating the age of

the Earth. There are, in certain rock-forming minerals,

colour-changes set up by radioactive causes. The minute and

curious marks so produced are known as haloes; for they surround,

in ringlike forms, minute particles of included substances which

contain radioactive elements. It is now well known how these

haloes are formed. The particle in the centre of the halo

contains uranium or thorium, and, necessarily, along with the

parent substance, the various elements derived from it. In the

process of transformation giving rise to these several derived

substances, atoms of helium—the alpha rays—projected with great

velocity into the surrounding mineral, occasion the colour

changes referred to. These changes are limited to the distance to

which the alpha rays penetrate; hence the halo is a spherical

volume surrounding the central substance.[1]

The time required to form a halo could be found if on the one

hand we could ascertain the number of alpha rays ejected from the

nucleus of the halo in, say, one year, and, on the other, if we

determined by experiment just how many alpha rays were required

to produce the same

[1] _Phil. Mag._, March, 1907 and February, 1910; also _Bedrock_,

January, 1913. See _Pleochroic Haloes_ in this volume.

21

amount of colour alteration as we perceive to extend around the

nucleus.

The latter estimate is fairly easily and surely made. But to know

the number of rays leaving the central particle in unit time we

require to know the quantity of radioactive material in the

nucleus. This cannot be directly determined. We can only, from

known results obtained with larger specimens of just such a

mineral substance as composes the nucleus, guess at the amount of

uranium, or it may be thorium, which may be present.

This method has been applied to the uranium haloes of the mica of

County Carlow.[1] Results for the age of the halo of from 20 to

400 millions of years have been obtained. This mica was probably

formed in the granite of Leinster in late Silurian or in Devonian

times.

The higher results are probably the least in error, upon the data

involved; for the assumption made as to the amount of uranium in

the nuclei of the haloes was such as to render the higher results

the more reliable.

This method is, of course, a radioactive method, and similar to

the method by helium storage, save that it is free of the risk of

error by escape of the helium, the effects of which are, as it

were, registered at the moment of its production, so that its

subsequent escape is of no moment.

[1] Joly and Rutherford, _Phil. Mag._, April, 1913.

22

REVIEW OF THE RESULTS

We shall now briefly review the results on the geological age of

the Earth.

By methods based on the approximate uniformity of denudative

effects in the past, a period of the order of 100 millions of

years has been obtained as the duration of our geological age;

and consistently whether we accept for measurement the sediments

or the dissolved sodium. We can give reasons why these

measurements might afford too great an age, but we can find

absolutely no good reason why they should give one much too low.

By measuring radioactive products ages have been found which,

while they vary widely among themselves, yet claim to possess

accuracy in their superior limits, and exceed those derived from

denudation from nine to fourteen times.

In this difficulty let us consider the claims of the radioactive

method in any of its forms. In order to be trustworthy it must be

true; (1) that the rate of transformation now shown by the parent

substance has obtained throughout the entire past, and (2) that

there were no other radioactive substances, either now or

formerly existing, except uranium, which gave rise to lead. As

regards methods based on the production of helium, what we have

to say will largely apply to it also. If some unknown source of

these elements exists we, of course, on our assumption

overestimate the age.

23

As regards the first point: In ascribing a constant rate of

change to the parent substance—which Becker (loc. cit.) describes

as "a simple though tremendous extrapolation"—we reason upon

analogy with the constant rate of decay observed in the derived

radioactive bodies. If uranium and thorium are really primary

elements, however, the analogy relied on may be misleading; at

least, it is obviously incomplete. It is incomplete in a

particular which may be very important: the mode of origin of

these parent bodies—whatever it may have been—is different to

that of the secondary elements with which we compare them. A

convergence in their rate of transformation is not impossible, or

even improbable, so far as we known.

As regards the second point: It is assumed that uranium alone of

the elements in radioactive minerals is ultimately transformed to

lead by radioactive changes. We must consider this assumption.

Recent advances in the chemistry of the radioactive elements has

brought out evidence that all three lines of radioactive descent

known to us—_i.e._ those beginning with uranium, with thorium,

and with actinium—alike converge to lead.[1] There are

difficulties in the way of believing that all the lead-like atoms

so produced ("isotopes" of lead, as Soddy proposes to call them)

actually remain as stable lead in the minerals. For one

[1] See Soddy's _Chemistry of the Radioactive Elements_ (Longmans,

Green & Co.).

24

thing there is sometimes, along with very large amounts of

thorium, an almost entire absence of lead in thorianites and

thorites. And in some urano—thorites the lead may be noticed to

follow the uranium in approximate proportionality,

notwithstanding the presence of large amounts of thorium.[1] This

is in favour of the assumption that all the lead present is

derived from the uranium. The actinium is present in negligibly

small amounts.

On the other hand, there is evidence arising from the atomic

weight of lead which seems to involve some other parent than

uranium. Soddy, in the work referred to, points this out. The

atomic weight of radium is well known, and uranium in its descent

has to change to this element. The loss of mass between radium

and uranium-derived lead can be accurately estimated by the

number of alpha rays given off. From this we get the atomic

weight of uranium-derived lead as closely 206. Now the best

determinations of the atomic weight of normal lead assign to this

element an atomic weight of closely

[1] It seems very difficult at present to suggest an end product

for thorium, unless we assume that, by loss of electrons, thorium

E, or thorium-lead, reverts to a substance chemically identical

with thorium itself. Such a change—whether considered from the

point of view of the periodic law or of the radioactive theory

would involve many interesting consequences. It is, of course,

quite possible that the nature of the conditions attending the

deposition of the uranium ores, many of which are comparatively

recent, are responsible for the difficulties observed. The

thorium and uranium ores are, again, specially prone to

alteration.

25

207. By a somewhat similar calculation it is deduced that

thorium-derived lead would possess the atomic weight of 208. Thus

normal lead might be an admixture of uranium- and thorium-derived

lead. However, as we have seen, the view that thorium gives rise

to stable lead is beset with some difficulties.

If we are going upon reliable facts and figures, we must, then,

assume: (a) That some other element than uranium, and genetically

connected with it (probably as parent substance), gives rise, or

formerly gave rise, to lead of heavier atomic weight than normal

lead. It may be observed respecting this theory that there is

some support for the view that a parent substance both to uranium

and thorium has existed or possibly exists. The evidence is found

in the proportionality frequently observed between the amounts of

thorium and uranium in the primary rocks.[1] Or: (b) We may meet

the difficulties in a simpler way, which may be stated as

follows: If we assume that all stable lead is derived from

uranium, and at the same time recognise that lead is not

perfectly homogeneous in atomic weight, we must, of necessity,

ascribe to uranium a similar want of homogeneity; heavy atoms of

uranium giving rise to heavy

[1] Compare results for the thorium content of such rocks

(appearing in a paper by the author Cong. Int. _de Radiologie et

d'Electricité_, vol. i., 1910, p. 373), and those for the radium

content, as collected in _Phil. Mag._, October, 1912, p. 697.

Also A. L. Fletcher, _Phil. Mag._, July, 1910; January, 1911, and

June, 1911. J. H. J. Poole, _Phil. Mag._, April, 1915

26

atoms of lead and light atoms of uranium generating light atoms

of lead. This assumption seems to be involved in the figures

upon, which we are going. Still relying on these figures, we

find, however, that existing uranium cannot give rise to lead of

normal atomic weight. We can only conclude that the heavier atoms

of uranium have decayed more rapidly than the lighter ones. In

this connection it is of interest to note the complexity of

uranium as recently established by Geiger, although in this case

it is assumed that the shorter-lived isotope bears the relation

of offspring to the longer-lived and largely preponderating

constituent. However, there does not seem to be any direct proof

of this as yet.

From these considerations it would seem that unless the atomic

weight of lead in uraninites, etc., is 206, the former complexity

and more accelerated decay of uranium are indicated in the data

respecting the atomic weights of radium and lead[1]. As an

alternative view, we may assume, as in our first hypothesis, that

some elementally different but genetically connected substance,

decaying along branching lines of descent at a rate sufficient to

practically remove the whole of it during geological time,

formerly existed. Whichever hypothesis we adopt

[1] Later investigation has shown that the atomic weight of lead

in uranium-bearing ores is about 206.6 (see Richards and Lembert,

_Journ. of Am. Claem. Soc._, July, 1914). This result gives support

to the view expressed above.

27

we are confronted by probabilities which invalidate

time-measurements based on the lead and helium ratio in minerals.

We have, in short, grave reason to question the measure of

uniformitarianism postulated in finding the age by any of the

known radioactive methods.

That we have much to learn respecting our assumptions, whether we

pursue the geological or the radioactive methods of approaching

the age of our era, is, indeed, probable. Whatever the issue it

is certain that the reconciling facts will leave us with much

more light than we at present possess either as respects the

Earth's history or the history of the radioactive elements. With

this necessary admission we leave our study of the Birth-Time of

the World.

It has led us a long way from Lucretius. We do not ask if other

Iliads have perished; or if poets before Homer have vainly sung,

becoming a prey to all-consuming time. We move in a greater

history, the landmarks of which are not the birth and death of

kings and poets, but of species, genera, orders. And we set out

these organic events not according to the passing generations of

man, but over scores or hundreds of millions of years.

How much Lucretius has lost, and how much we have gained, is

bound up with the question of the intrinsic value of knowledge

and great ideas. Let us appraise knowledge as we would the

Homeric poems, as some-

28

thing which ennobles life and makes it happier. Well, then, we

are, as I think, in possession today of some of those lost Iliads

and Odysseys for which Lucretius looked in vain.[1]

[1] The duration in the past of Solar heat is necessarily bound

up with the geological age. There is no known means (outside

speculative science) of accounting for more than about 30 million

years of the existing solar temperature in the past. In this

direction the age seems certainly limited to 100 million years.

See a review of the question by Dr. Lindemann in Nature, April

5th, 1915.

29

DENUDATION

THE subject of denudation is at once one of the most interesting

and one of the most complicated with which the geologist has to

deal. While its great results are apparent even to the most

casual observer, the factors which have led to these results are

in many cases so indeterminate, and in some cases apparently so

variable in influence, that thoughtful writers have even claimed

precisely opposite effects as originating from, the same cause.

Indeed, it is almost impossible to deal with the subject without

entering upon controversial matters. In the following pages I

shall endeavour to keep to broad issues which are, at the present

day, either conceded by the greater number of authorities on the

subject, or are, from their strictly quantitative character, not

open to controversy.

It is evident, in the first place, that denudation—or the wearing

away of the land surfaces of the earth—is mainly a result of the

circulation of water from the ocean to the land, and back again

to the ocean. An action entirely conditioned by solar heat, and

without which it would completely cease and further change upon

the land come to an end.

To what actions, then, is so great a potency of the

30

circulating water to be traced? Broadly speaking, we may classify

them as mechanical and chemical. The first involves the

separation of rock masses into smaller fragments of all sizes,

down to the finest dust. The second involves the actual solution

in the water of the rock constituents, which may be regarded as

the final act of disintegration. The rivers bear the burden both

of the comminuted and the dissolved materials to the sea. The mud

and sand carried by their currents, or gradually pushed along

their beds, represent the former; the invisible dissolved matter,

only to be demonstrated to the eye by evaporation of the water or

by chemical precipitation, represents the latter.

The results of these actions, integrated over geological time,

are enormous. The entire bulk of the sedimentary rocks, such as

sandstones, slates, shales, conglomerates, limestones, etc., and

the salt content of the ocean, are due to the combined activity

of mechanical and solvent denudation. We shall, later on, make an

estimate of the magnitude of the quantities actually involved.

In the Swiss valleys we see torrents of muddy water hurrying

along, and if we follow them up, we trace them to glaciers high

among the mountains. From beneath the foot of the glacier, we

find, the torrent has birth. The first debris given to the river

is derived from the wearing of the rocky bed along which the

glacier moves. The river of ice bequeaths to the river of

water—of which it is the parent—the spoils which it has won from

the rocks

31

The work of mechanical disintegration is, however, not restricted

to the glacier's bed. It proceeds everywhere over the surface of

the rocks. It is aided by the most diverse actions. For instance,

the freezing and expansion of water in the chinks and cracks in

those alpine heights where between sunrise and sunset the heat of

summer reigns, and between sunset and sunrise the cold of winter.

Again, under these conditions the mere change of surface

temperature from night to day severely stresses the surface

layers of the rocks, and, on the same principles as we explain

the fracture of an unequally heated glass vessel, the rocks

cleave off in slabs which slip down the steeps of the mountain

and collect as screes in the valley. At lower levels the

expansive force of vegetable growth is not unimportant, as all

will admit who have seen the strong roots of the pines

penetrating the crannies of the rocks. Nor does the river which

flows in the bed of the valley act as a carrier only. Listening

carefully we may detect beneath the roar of the alpine torrent

the crunching and knocking of descending boulders. And in the

potholes scooped by its whirling waters we recognise the abrasive

action of the suspended sand upon the river bed.

A view from an Alpine summit reveals a scene of remarkable

desolation (Pl. V, p. 40). Screes lie piled against the steep

slopes. Cliffs stand shattered and ready to fall in ruins. And

here the forces at work readily reveal themselves. An occasional

wreath of white smoke among

32

the far-off peaks, followed by a rumbling reverberation, marks

the fall of an avalanche. Water everywhere trickles through the

shaly _débris_ scattered around. In the full sunshine the rocks are

almost too hot to bear touching. A few hours later the cold is

deadly, and all becomes a frozen silence. In such scenes of

desolation and destruction, detrital sediments are actively being

generated. As we descend into the valley we hear the deep voice

of the torrents which are continually hurrying the disintegrated

rocks to the ocean.

A remarkable demonstration of the activity of mechanical

denudation is shown by the phenomenon of "earth pillars." The

photograph (Pl. IV.) of the earth pillars of the Val d'Hérens

(Switzerland) shows the peculiar appearance these objects

present. They arise under conditions where large stones or

boulders are scattered in a deep deposit of clay, and where much

of the denudation is due to water scour. The large boulders not

only act as shelter against rain, but they bind and consolidate

by their mere weight the clay upon which they rest. Hence the

materials underlying the boulders become more resistant, and as

the surrounding clays are gradually washed away and carried to

the streams, these compacted parts persist, and, finally, stand

like walls or pillars above the general level. After a time the

great boulders fall off and the underlying clay becomes worn by

the rainwash to fantastic spikes and ridges. In the Val d'Hérens

the earth pillars are formed

33

of the deep moraine stuff which thickly overlies the slopes of

the valley. The wall of pillars runs across the axis of the

valley, down the slope of the hill, and crosses the road, so that

it has to be tunnelled to permit the passage of traffic. It is

not improbable that some additional influence—possibly the

presence of lime—has hardened the material forming the pillars,

and tended to their preservation.

Denudation has, however, other methods of work than purely

mechanical; methods more noiseless and gentle, but not less

effective, as the victories of peace ate no less than those of

war.

Over the immense tracts of the continents chemical work proceeds

relentlessly. The rock in general, more especially the primary

igneous rock, is not stable in presence of the atmosphere and of

water. Some of the minerals, such as certain silicates and

carbonates, dissolve relatively fast, others with extreme

slowness. In the process of solution chemical actions are

involved; oxidation in presence of the free oxygen of the

atmosphere; attack by the feeble acid arising from the solution

of carbon dioxide in water; or, again, by the activity of certain

acids—humous acids—which originate in the decomposition of

vegetable remains. These chemical agents may in some instances,

_e.g._ in the case of carbonates such as limestone or

dolomite—bring practically the whole rock into solution. In other

instances—_e.g._ granites, basalts, etc.—they may remove some of

the

34

constituent minerals completely or partially, such as felspar,

olivine, augite, and leave more resistant substances to be

ultimately washed down as fine sand or mud into the river.

It is often difficult or impossible to appraise the relative

efficiency of mechanical and chemical denudation in removing the

materials from a certain area. There can be, indeed, little doubt

that in mountainous regions the mechanical effects are largely

predominant. The silts of glacial rivers are little different

from freshly-powdered rock. The water which carries them but

little different from the pure rain or snow which falls from the

sky. There has not been time for the chemical or solvent actions

to take place. Now while gravitational forces favour sudden shock

and violent motions in the hills, the effect of these on solvent

and chemical denudation is but small. Nor is good drainage

favourable to chemical actions, for water is the primary factor

in every case. Water takes up and removes soluble combinations of

molecules, and penetrates beneath residual insoluble substances.

It carries the oxygen and acids downwards through the soils, and

finally conveys the results of its own work to the rivers and

streams. The lower mean temperature of the mountains as well as

the perfect drainage diminishes chemical activities.

Hence we conclude that the heights are not generally favourable

to the purely solvent and chemical actions. It is on the

lower-lying land that soils tend to accumulate,

35

and in these the chief solvent and the chief chemical denudation

of the Earth are effected.

The solvent and chemical effects which go on in the

finely-divided materials of the soils may be observed in the

laboratory. They proceed faster than would be anticipated. The

observation is made by passing a measured quantity of water

backwards and forwards for some months through a tube containing

a few grammes of powdered rock. Finally the water is analysed,

and in this manner the amount of dissolved matter it has taken up

is estimated. The rock powder is examined under the microscope in

order to determine the size of the grains, and so to calculate

the total surface exposed to the action of the water. We must be

careful in such experiments to permit free oxidation by the

atmosphere. Results obtained in this way of course take no

account of the chemical effects of organic acids such as exist in

the soils. The quantities obtained in the laboratory will,

therefore, be deficient as compared with the natural results.

In this manner it has been found that fresh basalt exposed to

continually moving water will lose about 0.20 gramme per square

metre of surface per year. The mineral orthoclase, which enters

largely into the constitution of many granites, was found to lose

under the same conditions 0.025 gramme. A glassy lava (obsidian)

rich in silica and in the chemical constituents of an average

granite, was more resistant still; losing but 0.013 gramme per

square metre per year. Hornblende, a mineral

36

abundant in many rocks, lost 0.075 gramme. The mean of the

results showed that 0.08 gramme was washed in a year from each

square metre. Such results give us some indication of the rate at

which the work of solution goes on in the finely divided

soils.[1]

It might be urged that, as the mechanical break up of rocks, and

the production in this way of large surfaces, must be at the

basis of solvent and chemical denudation, these latter activities

should be predominant in the mountains. The answer to this is

that the soils rarely owe their existence to mechanical actions.

The alluvium of the valleys constitutes only narrow margins to

the rivers; the finer _débris_ from the mountains is rapidly

brought into the ocean. The soils which cover the greater part of

continental areas have had a very different origin.

In any quarry where a section of the soil and of the underlying

rock is visible, we may study the mode of formation of soils. Our

observations are, we will suppose, pursued in a granite quarry.

We first note that the material of the soil nearest the surface

is intermixed with the roots of grasses, trees, or shrubs.

Examining a handful of this soil, we see glistening flakes of

mica which plainly are derived from the original granite. Washing

off the finer particles, we find the largest remaining grains are

composed of the all but indestructible quartz.

[1] Proc. Roy. Irish Acad., VIII., Ser. A, p. 21.

37

This also is from the granite. Some few of the grains are of

chalky-looking felspar; again a granitic mineral. What is the

finer silt we have washed off? It, too, is composed of mineral

particles to a great extent; rock dust stained with iron oxide

and intermixed with organic remains, both animal and vegetable.

But if we make a chemical analysis of the finer silt we find that

the composition is by no means that of the granite beneath. The

chemist is able to say, from a study of his results, that there

has been, in the first place, a large loss of material attending

the conversion of the granite to the soil. He finds a

concentration of certain of the more resistant substances of the

granite arising from the loss of the less resistant. Thus the

percentage amount of alumina is increased. The percentage of iron

is also increased. But silica and most other substances show a

diminished percentage. Notably lime has nearly disappeared. Soda

is much reduced; so is magnesia. Potash is not so completely

abstracted. Finally, owing to hydration, there is much more

combined water in the soil than in the rock. This is a typical

result for rocks of this kind.

Deeper in the soil we often observe a change of texture. It has

become finer, and at the same time the clay is paler in colour.

This subsoil represents the finer particles carried by rain from

above. The change of colour is due to the state of the iron which

is less oxidised low down in the soil. Beneath the subsoil the

soil grows

38

again coarser. Finally, we recognise in it fragments of granite

which ever grow larger as we descend, till the soil has become

replaced by the loose and shattered rock. Beneath this the only

sign of weathering apparent in the rock is the rusty hue imparted

by the oxidised iron which the percolating rain has leached from

iron-bearing minerals.

The soil we have examined has plainly been derived in situ from

the underlying rock. It represents the more insoluble residue

after water and acids have done their work. Each year there must

be a very slow sinking of the surface, but the ablation is

infinitesimal.

The depth of such a soil may be considerable. The total surface

exposed by the countless grains of which it is composed is

enormous. In a cubic foot of average soil the surface area of the

grains may be 50,000 square feet or more. Hence a soil only two

feet deep may expose 100,000 square feet for each square foot of

surface area.

It is true that soils formed in this manner by atmospheric and

organic actions take a very long time to grow. It must be

remembered, however, that the process is throughout attended by

the removal in solution: of chemically altered materials.

Considerations such as the foregoing must convince us that while

the accumulation of the detrital sediments around the continents

is largely the result of activities progressing on the steeper

slopes of the land, that is,

39

among the mountainous regions, the feeding of the salts to the

ocean arises from the slower work of meteorological and organic

agencies attacking the molecular constitution of the rocks;

processes which best proceed where the drainage is sluggish and

the quiescent conditions permit of the development of abundant

organic growth and decay.

Statistics of the solvent denudation of the continents support

this view. Within recent years a very large amount of work has

been expended on the chemical investigation of river waters of

America and of Europe. F. W. Clarke has, at the expense of much

labour, collected and compared these results. They are expressed

as so many tonnes removed in solution per square mile per annum.

For North America the result shows 79 tonnes so removed; for

Europe 100 tonnes. Now there is a notable difference between the

mean elevations of these two continents. North America has a mean

elevation of 700 metres over sea level, whereas the mean

elevation of Europe is but 300 metres. We see in these figures

that the more mountainous land supplies less dissolved matter to

the ocean than the land of lower elevation, as our study has led

us to expect.

We have now considered the source of the detrital sediments, as

well as of the dissolved matter which has given to the ocean, in

the course of geological time, its present gigantic load of

salts. It is true there are further solvent and chemical effects

exerted by the sea water

40

upon the sediments discharged into it; but we are justified in

concluding that, relatively to the similar actions taking place

in the soils, the solvent and chemical work of the ocean is

small. The fact is, the deposited detrital sediments around the

continents occupy an area small when contrasted with the vast

stretches of the land. The area of deposition is much less than

that of denudation; probably hardly as much as one twentieth.

And, again, the conditions of aeration and circulation which

largely promote chemical and solvent denudation in the soils are

relatively limited and ineffective in the detrital oceanic

deposits.

The summation of the amounts of dissolved and detrital materials

which denudation has brought into the ocean during the long

denudative history of the Earth, as we might anticipate, reveals

quantities of almost unrealisable greatness. The facts are among

the most impressive which geological science has brought to

light. Elsewhere in this volume they have been mentioned when

discussing the age of the Earth. In the present connection,

however, they are deserving of separate consideration.

The basis of our reasoning is that the ocean owes its saltness

mainly if not entirely to the denudative activities we have been

considering. We must establish this.

We may, in the first place, say that any other view at once

raises the greatest difficulties. The chemical composition of the

detrital sediments which are spread over

41

the continents and which build up the mountains, differs on the

average very considerably from that of the igneous rocks. We know

the former have been derived from the latter, and we know that

the difference in the composition of the two classes of materials

is due to the removal in solution of certain of the constituents

of the igneous rocks. But the ocean alone can have received this

dissolved matter. We know of no other place in which to look for

it. It is true that some part of this dissolved matter has been

again rejected by the ocean; thus the formation of limestone is

largely due to the abstraction of lime from sea water by organic

and other agencies. This, however, in no way relieves us of the

necessity of tracing to the ocean the substances dissolved from

the igneous rocks. It follows that we have here a very causa for

the saltness of the ocean. The view that the ocean "was salt from

the first" is without one known fact to support it, and leaves us

with the burden of the entire dissolved salts of geological time

to dispose of—Where and how?

The argument we have outlined above becomes convincingly strong

when examined more closely. For this purpose we first compare the

average chemical composition of the sedimentary and the igneous

rocks. The following table gives the percentages of the chief

chemical constituents: [1]

[1] F. W. Clarke: _A Preliminary Study of Chemical Denudation_,

p. 13

42

Igneous.        Sedimentary.

Silica (SiO_2) -             59.99           58.51

Alumina (Al_2O_3) -           15.04           13.07

Ferric oxide (F_2O_3) -       2.59            3.40

Ferrous oxide (FeO) -       3.34            2.00

Magnesia (MgO) -            3.89            2.52

Lime (CaO) -                 4.81            5.42

Soda (Na_2O) -                3.41            1.12

Potash (K_2O) -               2.95            2.80

Water (H_2O) -                1.92            4.28

Carbon dioxide (CO_2) -       --             4.93

Minor constituents -        2.06            1.95

100.00          100.00

In the derivation of the sediments from the igneous rocks there

is a loss by solution of about 33 per cent; _i.e._ 100 tons of

igneous rock yields rather less than 70 tons of sedimentary rock.

This involves a concentration in the sediments of the more

insoluble constituents. To this rule the lime-content appears to

be an exception. It is not so in reality. Its high value in the

sediments is due to its restoration from the ocean to the land.

The magnesia and potash are, also, largely restored from the

ocean; the former in dolomites and magnesian limestones; the

latter in glauconite sands. The iron of the sediments shows

increased oxidation. The most notable difference in the two

analyses appears, however, in the soda percentages. This falls

from 3.41 in the igneous rock to 1.12 in the average sediment.

Indeed, this

43

deficiency of soda in sedimentary rocks is so characteristic of

secondary rocks that it may with some safety be applied to

discriminate between the two classes of substances in cases where

petrological distinctions of other kinds break down.

To what is this so marked deficiency of soda to be ascribed? It

is a result of the extreme solubility of the salts of sodium in

water. This has not only rendered its deposition by evaporation a

relatively rare and unimportant incident of geological history,

but also has protected it from abstraction from the ocean by

organic agencies. The element sodium has, in fact, accumulated in

the ocean during the whole of geological time.

We can use the facts associated with the accumulation of sodium

salts in the ocean as a means of obtaining additional support to

the view, that the processes of solvent denudation are

responsible for the saltness of the ocean. The new evidence may

be stated as follows: Estimates of the amounts of sedimentary

rock on the continents have repeatedly been made. It is true that

these estimates are no more than approximations. But they

undoubtedly _are_ approximations, and as such may legitimately be

used in our argument; more especially as final agreement tends to

check and to support the several estimates which enter into

them.

The most recent and probable estimates of the sediments on the

land assign an average thickness of one mile of

44

secondary rocks over the land area of the world. To this some

increase must be made to allow for similar materials concealed in

the ocean, principally around the continental margins. If we add

10 per cent. and assign a specific gravity of 2.5 we get as the

mass of the sediments 64 x 10^16 tonnes. But as this is about 67

per cent. of the parent igneous rock—_i.e._ the average igneous

rock from which the sediments are derived—we conclude that the

primary denuded rock amounted to a mass of about 95 x 10^16

tonnes.

Now from the mean chemical composition of the secondary rocks we

calculate that the mass of sediments as above determined contains

0.72 x10^16 tonnes of the sodium oxide, Na_2O. If to this amount we

add the quantity of sodium oxide which must have been given to

the ocean in order to account for the sodium salts contained

therein, we arrive at a total quantity of oxide of sodium which

must be that possessed by the primary rock before denudation

began its work upon it. The mass of the ocean being well

ascertained, we easily calculate that the sodium in the ocean

converted to sodium oxide amounts to 2.1 x 10^16 tonnes. Hence

between the estimated sediments and the waters of the ocean we

can account for 2.82 x 10^16 tonnes of soda. When now we put this

quantity back into the estimated mass of primary rock we find

that it assigns to the primary rock a soda percentage of 3.0. On

the average analysis given above this should be 3.41 per cent.

The agreement,

45

all things considered, more especially the uncertainty in the

estimate of the sediments, is plainly in support of the view that

oceanic salts are derived from the rocks; if, indeed, it does not

render it a certainty.

A leading and fundamental inference in the denudative history of

the Earth thus finds support: indeed, we may say, verification.

In the light of this fact the whole work of denudation stands

revealed. That the ocean began its history as a vast fresh-water

envelope of the Globe is a view which accords with the evidence

for the primitive high temperature of the Earth. Geological

history opened with the condensation of an atmosphere of immense

extent, which, after long fluctuations between the states of

steam and water, finally settled upon the surface, almost free of

matter in solution: an ocean of distilled water. The epoch of

denudation then began. It will, probably, continue till the

waters, undergoing further loss of thermal energy, suffer yet

another change of state, when their circulation will cease and

their attack upon the rocks come to an end.

From what has been reviewed above it is evident that the sodium

in the ocean is an index of the total activity of denudation

integrated over geological time. From this the broad facts of the

results of denudation admit of determination with considerable

accuracy. We can estimate the amount of rock which has been

degraded by solvent and chemical actions, and the amount of

sediments which has been derived from it. We are,

46

thus, able to amend our estimate of the sediments which, as

determined by direct observation, served to support the basis of

our argument.

We now go straight to the ocean for the amount of sodium of

denudative origin. There may, indeed, have been some primitive

sodium dissolved by a more rapid denudation while the Earth's

surface was still falling in temperature. It can be shown,

however, that this amount was relatively small. Neglecting it we

may say with safety that the quantity of sodium carried into the

ocean by the rivers must be between 14,000 and 15,000 million

million tonnes: _i.e._ 14,500 x 10^12 tonnes, say.

Keeping the figures to round numbers we find that this amount of

sodium involves the denudation of about 80 x 10^16 tonnes of

average igneous rock to 53 x 1016 tonnes of average sediment.

From these vast quantities we know that the parent rock denuded

during geological time amounted to some 300 million cubic

kilometres or about seventy million cubic miles. The sediments

derived therefrom possessed a bulk of 220 million cubic

kilometres or fifty million cubic miles. The area of the land

surface of the Globe is 144 million square kilometres. The parent

rock would have covered this to a uniform depth of rather more

than two kilometres, and the derived sediment to more than 1.5

kilometres, or about one mile deep.

The slow accomplishment of results so vast conveys some idea of

the great duration of geological time.

47

The foregoing method of investigating the statistics of solvent

denudation is capable of affording information not only as to the

amount of sediments upon the land, but also as to the quantity

which is spread over the floor of the ocean.

We see this when we follow the fate of the 33 per cent. of

dissolved salts which has been leached from the parent igneous

rock, and the mass of which we calculate from the ascertained

mass of the latter, to be 27 x 10^16 tonnes. This quantity was at

one time or another all in the ocean. But, as we saw above, a

certain part of it has been again abstracted from solution,

chiefly by organic agencies. Now the abstracted solids have not

been altogether retained beneath the ocean. Movements of the land

during geological time have resulted in some portion being

uplifted along with other sediments. These substances constitute,

mainly, the limestones.

We see, then, that the 27 x 10^16 tonnes of substances leached

from the parent igneous rocks have had a threefold destination.

One part is still in solution; a second part has been

precipitated to the bottom of the ocean; a third part exists on

the land in the form of calcareous rocks.

Observation on the land sediments shows that the calcareous rocks

amount to about 5 per cent. of the whole. From this we find that

3 x 10^16 tonnes, approximately, of such rocks have been taken

from the ocean. This accounts for one of the three classes of

material

48

into which the original dissolved matter has been divided.

Another of the three quantities is easily estimated: the amount

of matter still in solution in the ocean. The volume of the ocean

is 1,414 million cubic kilometres and its mass is 145 x 10^16

tonnes. The dissolved salts in it constitute 3.4 per cent. of its

mass; or, rather more than 5 x 10^16 tonnes. The limestones on the

land and the salts in the sea water together make up about 8 x

10^16 tonnes. If we, now, deduct this from the total of 27 x 10^16

tonnes, we find that about 19 x 10^16 tonnes must exist as

precipitated matter on the floor of the ocean.

The area of the ocean is 367 x 10^12 square metres, so that if the

precipitated sediment possesses an average specific gravity of

2.5, it would cover the entire floor to a uniform depth of 218

metres; that is 715 feet. This assumes that there was uniform

deposition of the abstracted matter over the floor of the ocean.

Of course, this assumption is not justifiable. It is certain that

the rate of deposition on the floor of the sea has varied

enormously with various conditions—principally with the depth.

Again, it must be remembered that this estimate takes no account

of solid materials otherwise brought into the oceanic deposits;

_e.g._, by wind-transported dust from the land or volcanic

ejectamenta in the ocean depths. It is not probable, however,

that any considerable addition to the estimated mean depth of

deposit from such sources would be allowable.

49

The greatness of the quantities involved in these determinations

is almost awe inspiring. Take the case of the dissolved salts in

the ocean. They are but a fraction, as we have seen, of the total

results of solvent denudation and represent the integration of

the minute traces contributed by the river water. Yet the common

salt (chloride of sodium) alone, contained in the ocean, would,

if abstracted and spread over the dry land as a layer of rock

salt having a specific gravity of 2.2, cover the whole to a depth

of 107 metres or 354 feet. The total salts in solution in the

ocean similarly spread over the land would increase the depth of

the layer to 460 feet. After considering what this means we have

to remember that this amount of matter now in solution in the

seas is, in point of fact, less than a fifth part of the total

dissolved from the rocks during geological time.

The transport by denudation of detrital and dissolved matter from

the land to the ocean has had a most important influence on the

events of geological history. The existing surface features of

the earth must have been largely conditioned by the dynamical

effects arising therefrom. In dealing with the subject of

mountain genesis we will, elsewhere, see that all the great

mountain ranges have originated in the accumulation of the

detrital sediments near the shore in areas which, in consequence

of the load, gradually became depressed and developed into

synclines of many thousands of feet in depth. The most impressive

surface features of the Globe originated

50

in this manner. We will see too that these events were of a

rhythmic character; the upraising of the mountains involving

intensified mechanical denudation over the elevated area and in

this way an accelerated transport of detritus to the sea; the

formation of fresh deposits; renewed synclinal sinking of the sea

floor, and, finally, the upheaval of a younger mountain range.

This extraordinary sequence of events has been determined by the

events of detrital denudation acting along with certain general

conditions which have all along involved the growth of

compressive stresses in the surface crust of the Earth.

The effects of purely solvent denudation are less easily traced,

but, very probably, they have been of not less importance. I

refer here to the transport from the land to the sea of matter in

solution.

Solvent denudation, as observed above, takes place mainly in the

soils and in this way over the more level continental areas. It

has resulted in the removal from the land and transfer to the

ocean of an amount of matter which represents a uniform layer of

one half a kilometre; that is of more than 1,600 feet of rock.

The continents have, during geological time, been lightened to

this extent. On the other hand all this matter has for the

greater part escaped the geosynclines and become uniformly

diffused throughout the ocean or precipitated over its floor

principally on the continental slopes before the great depths are

reached. Of this material the ocean

51

waters contain in solution an amount sufficient to increase their

specific gravity by 2.7 per cent.

Taking the last point first, it is interesting to note the

effects upon the bulk of the ocean which has resulted from the

matter dissolved in it. From the known density of average sea

water we find that 100 ccs. of it weigh just 102.7 grammes. Of

this 3.5 per cent. by weight are solids in solution. That is to

say, 3.594 grammes. Hence the weight of water present is 99.1

grammes, or a volume of 99.1 ccs. From this we see that the salts

present have increased the volume by 0.9 ccs. or 0.9 per cent.

The average depth of the ocean is 2,000 fathoms or 3,700 metres.

The increase of depth due to salts dissolved in the ocean has

been, therefore, 108 feet or 33.24 metres. This result assumes

that there has been no increased elastic compression due to the

increased pressure, and no change of compressional elastic

properties. We may be sure that the rise on the shore line of the

land has not been less than 100 feet.

We see then that as the result of solvent denudation we have to

do with a heavier and a deeper ocean, expanded in volume by

nearly one per cent. and the floor of which has become raised, on

an average, about 700 feet by precipitated sediment.

One of the first conceptions, which the student of geology has to

dismiss from his mind, is that of the immobility or rigidity of

the Earth's crust. The lane, we live on sways even to the gentle

rise and fail of ocean tides

52

around the coasts. It suffers its own tidal oscillations due to

the moon's attractions. Large tracts of semi-liquid matter

underlie it. There is every evidence that the raised features of

the Globe are sustained by such pressures acting over other and

adjacent areas as serve to keep them in equilibrium against the

force of gravity. This state of equilibrium, which was first

recognised by Pratt, as part of the dynamics of the Earth's

crust, has been named isostasy. The state of the crust is that of

"mobile equilibrium."

The transfer of matter from the exposed land surfaces to the

sub-oceanic slopes of the continents and the increase in the

density of the ocean, must all along have been attended by

isostatic readjustment. We cannot take any other view. On the one

hand the land was being lightened; on the other the sea was

increasing in mass and depth and the flanks of the continents

were being loaded with the matter removed from the land and borne

in solution to the ocean. How important the resulting movements

must have been may be gathered from the fact that the existing

land of the Globe stands at a mean elevation of no more than

2,000 feet above sea level. We have seen that solvent denudation

removed over 1,600 feet of rock. But we have no evidence that on

the whole the elevation of land in the past was ever very

different from what it now is.

We have, then, presented to our view the remarkable fact that

throughout the past, and acting with extreme

53

slowness, the land has steadily been melted down into the sea and

as steadily been upraised from the waters. It is possible that

the increased bulk of the ocean has led to a certain diminution

of the exposed land area. The point is a difficult one. One thing

we may without much risk assume. The sub-aereal current of

dissolved matter from the land to the ocean was accompanied by a

sub-crustal flux from the ocean areas to the land areas; the

heated viscous materials creeping from depths far beneath the

ocean floor to depths beneath the roots of the mountains which

arose around the oceans. Such movements took ages for their

accomplishment. Indeed, they have been, probably, continuous all

along and are still proceeding. A low degree of viscosity will

suffice to permit of movements so slow. Superimposed upon these

movements the rhythmic alternations of depression and elevation

of the geosynclines probably resulted in releasing the crust from

local accumulation of strains arising in the more rigid surface

materials. The whole sequence of movements presents an

extraordinary picture of pseudo-vitality—reminding us of the

circulatory and respiratory systems of a vast organism.

All great results in our universe are founded in motions and

forces the most minute. In contemplating the Cause or the Effect

we stand equally impressed with the spectacle presented to us. We

shall now turn from the great effects of denudation upon the

history and evolution of a world and consider for a moment

activities

54

so minute in detail that their operations will probably for ever

elude our bodily senses, but which nevertheless have necessarily

affected and modified the great results we have been

considering.

The ocean a little way from the land is generally so free from

suspended sediments that it has a blackness as of ink. This

blackness is due to its absolute freedom from particles

reflecting the sun's light. The beautiful blue of the Swiss and

Italian lakes is due to the presence of very fine particles

carried into them by the rivers; the finest flour of the

glaciers, which remain almost indefinitely suspended in the

water. But in the ocean it is only in those places where rapid

currents running over shallows stir continually the sediments or

where the fresh water of a great river is carried far from the

land, that the presence of silt is to be observed. The beautiful

phenomenon of the coal-black sea is familiar to every yachtsman

who has sailed to the west of our Islands.[1]

There is, in fact, a very remarkable difference in the manner of

settlement of fine sediments in salt and in fresh water. We are

here brought into contact with one of those subtle yet

influential natural actions the explanation of which involves

scientific advance along many apparently unconnected lines of

investigation.

[1] See Tyndall's Voyage to Algeria in _Fragments of Science._ The

cause of the blue colour of the lakes has been discussed by

various observers, not always with agreement.

55

It is easy to observe in the laboratory the fact of the different

behaviour of salt and fresh water towards finely divided

substances. The nature of the insoluble substance is not

important.

We place, in a good light, two glass vessels of equal dimensions;

the one filled with sea water, the other with fresh water. Into

each we stir the same weight of very finely powdered slate: just

so much as will produce a cloudiness. In a few hours we find the

sea water limpid. The fresh water is still cloudy, however; and,

indeed, may be hardly different in appearance from what it was at

starting. In itself this is a most extraordinary experiment. We

would have anticipated quite the opposite result owing to the

greater density of the sea water.

But a still more interesting experiment remains to be carried

out. In the sea water we have many different salts in solution.

Let us see if these salts are equally responsible for the result

we have obtained. For this purpose we measure out quantities of

sodium chloride and magnesium chloride in the proportion in which

they exist in sea water: that is about as seven to one. We add

such an equal amount of water to each as represents the dilution

of these salts in sea water. Then finally we stir a little of the

finely powdered slate into each. It will be found that the

magnesium chloride, although so much more dilute than the sodium

chloride, is considerably more active in clearing out the

suspension. We may now try such marine salts as magnesium

sulphate,

56

or calcium sulphate against sodium chloride; keeping the marine

proportions. Again we find that the magnesium and calcium salts

are the most effective, although so much more dilute than the

sodium salt.

There is no visible clue to the explanation of these results. But

we must conclude as most probable that some action is at work in

the sea water and in the salt solutions which clumps or

flocculates the sediment. For only by the gathering of the

particles together in little aggregates can we explain their

rapid fall to the bottom. It is not a question of viscosity

(_i.e._ of resistance to the motion of the particles), for the

salt solutions are rather more viscous than the fresh water.

Still more remarkable is the fact that every dissolved substance

will not bring about the result. Thus if we dissolve sugar in

water we find that, if anything, the silt settles more slowly in

the sugar solution than in fresh water.

Now there is one effect produced by the solution of such salts as

we have dealt with which is not produced by such bodies as sugar.

The water is rendered a conductor of electricity. Long ago

Faraday explained this as due to the presence of free atoms of

the dissolved salt in the solution, carrying electric charges. We

now speak of the salt as "ionised." That is it is partly split up

into ions or free electrified atoms of chlorine, sodium,

magnesium, etc., according to the particular salt in solution.

This fact leads us to think that these electrified

57

atoms moving about in the solution may be the cause of the

clumping or flocculation. Such electrified atoms are absent from

the sugar solution: sugar does not become "ionised" when it is

dissolved.

The suspicion that the free electrified atoms play a part in the

phenomenon is strengthened when we recall the remarkable

difference in the action of sodium chloride and magnesium

chloride. In each of the solutions of these substances there are

free chlorine atoms each of which carries a single charge of

negative electricity. As these atoms are alike in both solutions

the different behaviour of the solutions cannot be due to the

chlorine. But the metallic atom is very different in the two

cases. The ionised sodium atom is known to be _monad_ or carries

but _one_ positive charge; whereas the magnesium atom is _diad_ and

carries _two_ positive charges. If, then, we assume that the

metallic, positively electrified atom is in each case

responsible, we have something to go on. It may be now stated

that it has been found by experiment and supported by theory that

the clumping power of an ion rises very rapidly with its valency;

that is with the number of unit charges associated with it. Thus

diads such as magnesium, calcium, barium, etc., are very much

more efficient than monads such as sodium, potassium, etc., and

again, triads such as aluminium are, similarly, very much more

powerful than diad atoms. Here, in short, we have arrived at the

active cause of the phenomenon. Its inner mechanism

58

is, however, harder to fathom. A plausible explanation can be

offered, but a study of it would take us too far. Sufficient has

been said to show the very subtile nature of the forces at work.

We have here an effect due to the sea salts derived by denudation

from the land which has been slowly augmenting during geological

time. It is certain that the ocean was practically fresh water in

remote ages. During those times the silt from the great rivers

would have been carried very far from the land. A Mississippi of

those ages would have sent its finer suspensions far abroad on a

contemporary Gulf stream: not improbably right across the

Atlantic. The earlier sediments of argillaceous type were not

collected in the geosynclines and the genesis of the mountains

was delayed proportionately. But it was, probably, not for very

long that such conditions prevailed. For the accumulation of

calcium salts must have been rapid, and although the great

salinity due to sodium salts was of slow growth the salts of the

diad element calcium must have soon introduced the cooperation of

the ion in the work of building the mountain.

59

THE ABUNDANCE OF LIFE [1]

WE had reached the Pass of Tre Croci[2]and from a point a little

below the summit, looked eastward over the glorious Val Buona.

The pines which clothed the floor and lower slopes of the valley,

extended their multitudes into the furthest distance, among the

many recesses of the mountains, and into the confluent Val di

Misurina. In the sunshine the Alpine butterflies flitted from

stone to stone. The ground at our feet and everywhere throughout

the forests teamed with the countless millions of the small black

ants.

It was a magnificent display of vitality; of the aggressiveness

of vitality, assailing the barren heights of the limestone,

wringing a subsistence from dead things. And the question

suggested itself with new force: why the abundance of life and

its unending activity?

In trying to answer this question, the present sketch

originated.

I propose to refer for an answer to dynamic considerations. It is

apparent that natural selection can only be concerned in a

secondary way. Natural selection defines

[1] Proc. Roy. Dublin Soc., vol. vii., 1890.

[2] In the Dolomites of Southeast Tyrol; during the summer of

1890. Much of what follows was evolved in discussion with my

fellow-traveller, Henry H. Dixon. Much of it is his.

60

a certain course of development for the organism; but very

evidently some property of inherent progressiveness in the

organism must be involved. The mineral is not affected by natural

selection to enter on a course of continual variation and

multiplication. The dynamic relations of the organism with the

environment are evidently very different from those of inanimate

nature.

GENERAL DYNAMIC CONDITIONS ATTENDING INANIMATE ACTIONS

It is necessary, in the first place, to refer briefly to the

phenomena attending the transfer of energy within and into

inanimate material systems. It is not assumed here that these

phenomena are restricted in their sphere of action to inanimate

nature. It is, in fact, very certain that they are not; but while

they confer on dead nature its own dynamic tendencies, it will

appear that their effects are by various means evaded in living

nature. We, therefore, treat of them as characteristic of

inanimate actions. We accept as fundamental to all the

considerations which follow the truth of the principle of the

Conservation of Energy.[1]

[1] "The principle of the Conservation of Energy has acquired so

much scientific weight during the last twenty years that no

physiologist would feel any confidence in an experiment which

showed a considerable difference between the work done by the

animal and the balance of the account of Energy received and

spent."—Clerk Maxwell, _Nature_, vol. xix., p. 142. See also

Helmholtz _On the Conservation of Force._

61

Whatever speculations may be made as to the course of events very

distant from us in space, it appears certain that dissipation of

energy is at present actively progressing throughout our sphere

of observation in inanimate nature. It follows, in fact, from the

second law of thermodynamics, that whenever work is derived from

heat, a certain quantity of heat falls in potential without doing

work or, in short, is dissipated. On the other hand, work may be

entirely converted into heat. The result is the heat-tendency of

the universe. Heat, being an undirected form of energy, seeks, as

it were, its own level, so that the result of this heat-tendency

is continual approach to uniformity of potential.

The heat-tendency of the universe is also revealed in the

far-reaching "law of maximum work," which defines that chemical

change, accomplished without the intervention of external energy,

tends to the production of the body, or system of bodies, which

disengage the greatest quantity of heat.[1] And, again, vast

numbers of actions going on throughout nature are attended by

dissipatory thermal effects, as those arising from the motions of

proximate molecules (friction, viscosity), and from the fall of

electrical potential.

Thus, on all sides, the energy which was once most probably

existent in the form of gravitational potential, is being

dissipated into unavailable forms. We must

[1] Berthelot, _Essai de Mécanique Chimique._

62

recognize dissipation as an inevitable attendant on inanimate

transfer of energy.

But when we come to consider inanimate actions in relation to

time, or time-rate of change, we find a new feature in the

phenomena attending transfer of energy; a feature which is really

involved in general statements as to the laws of physical

interactions.[1] It is seen, that the attitude of inanimate

material systems is very generally, if not in all cases,

retardative of change—opposing it by effects generated by the

primary action, which may be called "secondary" for convenience.

Further, it will be seen that these secondary effects are those

concerned in bringing about the inevitable dissipation.

As example, let us endeavour to transfer gravitational potential

energy contained in a mass raised above the surface of the Earth

into an elastic body, which we can put into compression by

resting the weight upon it. In this way work is done against

elastic force and stored as elastic potential energy. We may deal

with a metal spring, or with a mass of gas contained in a

cylinder fitted with a piston upon which the weight may be

placed. In either case we find the effect of compression is to

raise the temperature of the substance, thus causing its

[1] Helmholtz, _Ice and Glaciers._ Atkinson's collection of his

Popular Lectures. First Series, p.120. Quoted by Tate, _Heat_,

p. 311.

63

expansion or increased resistance to the descent of the weight.

And this resistance continues, with diminishing intensity, till

all the heat generated is dissipated into the surrounding medium.

The secondary effect thus delays the final transfer of energy.

Again, if we suppose the gas in the cylinder replaced by a vapour

in a state of saturation, the effect of increased pressure, as of

a weight placed upon the piston, is to reduce the vapour to a

liquid, thereby bringing about a great diminution of volume and

proportional loss of gravitational potential by the weight. But

this change will by no means be brought about instantaneously.

When a little of the vapour is condensed, this portion parts with

latent heat of vaporisation, increasing the tension of the

remainder, or raising its point of saturation, so that before the

weight descends any further, this heat has to escape from the

cylinder.

Many more such cases might be cited. The heating of india-rubber

when expanded, its cooling when compressed, is a remarkable one;

for at first sight it appears as if this must render it

exceptional to the general law, most substances exhibiting the

opposite thermal effects when stressed. However, here, too, the

action of the stress is opposed by the secondary effects

developed in the substance; for it is found that this substance

contracts when heated, expands when cooled. Again, ice being a

substance which contracts in melting, the effect of pressure is

to facilitate melting, lowering its freezing point. But

64

so soon as a little melting occurs, the resulting liquid calls on

the residual ice for an amount of heat equivalent to the latent

heat of liquefaction, and so by cooling the whole, retards the

change.

Such particular cases illustrate a principle controlling the

interaction of matter and energy which seems universal in

application save when evaded, as we shall see, by the ingenuity

of life. This principle is not only revealed in the researches of

the laboratory; it is manifest in the history of worlds and solar

systems. Thus, consider the effects arising from the aggregation

of matter in space under the influence of the mutual attraction

of the particles. The tendency here is loss of gravitational

potential. The final approach is however retarded by the

temperature, or vis viva of the parts attending collision and

compression. From this cause the great suns of space radiate for

ages before the final loss of potential is attained.

Clerk Maxwell[1] observes on the general principle that less

force is required to produce a change in a body when the change

is unopposed by constraints than when it is subjected to such.

From this if we assume the external forces acting upon a system

not to rise above a certain potential (which is the order of

nature), the constraints of secondary actions may, under certain

circumstances, lead to final rejection of some of the energy, or,

in any

[1] _Theory of Heat_, p. 131.

65

case, to retardation of change in the system—dissipation of

energy being the result.[1]

As such constraints seem inherently present in the properties of

matter, we may summarise as follows:

_The transfer of energy into any inanimate material system is

attended by effects retardative to the transfer and conducive to

dissipation._

Was this the only possible dynamic order ruling in material

systems it is quite certain the myriads of ants and pines never

could have been, except all generated by creative act at vast

primary expenditure of energy. Growth and reproduction would have

been impossible in systems which retarded change at every step

and never proceeded in any direction but in that of dissipation.

Once created, indeed, it is conceivable that, as heat engines,

they might have dragged out an existence of alternate life and

death; life in the hours of sunshine, death in hours of darkness:

no final death, however, their lot, till their parts were simply

worn out by long use, never made good by repair. But the

sustained and increasing activity of organized nature is a fact;

therefore some other order of events must be possible.

[1] The law of Least Action, which has been applied, not alone in

optics, but in many mechanical systems, appears physically based

upon the restraint and retardation opposing the transfer of

energy in material systems.

66

GENERAL DYNAMIC CONDITIONS ATTENDING ANIMATE ACTIONS

What is the actual dynamic attitude of the primary organic

engine—the vegetable organism? We consider, here, in the first

place, not intervening, but resulting phenomena.

The young leaf exposed to solar radiation is small at first, and

the quantity of radiant energy it receives in unit of time cannot

exceed that which falls upon its surface. But what is the effect

of this energy? Not to produce a retardative reaction, but an

accelerative response: for, in the enlarging of the leaf by

growth, the plant opens for itself new channels of supply.

If we refer to "the living protoplasm which, with its unknown

molecular arrangement, is the only absolute test of the cell and

of the organism in general,[1] we find a similar attitude towards

external sources of available energy. In the act of growth

increased rate of assimilation is involved, so that there is an

acceleration of change till a bulk of maximum activity is

attained. The surface, finally, becomes too small for the

absorption of energy adequate to sustain further increase of mass

(Spencer[2]), and the acceleration ceases. The waste going on in

the central parts is then just balanced by the renewal at the

surface. By division, by spreading of the mass, by

[1] Claus, _Zoology_, p. 13.

[2] Geddes and Thomson, _The Evolution of Sex_, p. 220.

67

out-flowing processes, the normal activity of growth may be

restored. Till this moment nothing would be gained by any of

these changes. One or other of them is now conducive to

progressive absorption of energy by the organism, and one or

other occurs, most generally the best of them, subdivision. Two

units now exist; the total mass immediately on division is

unaltered, but paths for the more abundant absorption of energy

are laid open.

The encystment of the protoplasm (occurring under conditions upon

which naturalists do not seem agreed[1]) is to all appearance

protective from an unfavourable environment, but it is often a

period of internal change as well, resulting in a segregation

within the mass of numerous small units, followed by a breakup of

the whole into these units. It is thus an extension of the basis

of supply, and in an impoverished medium, where unit of surface

is less active, is evidently the best means of preserving a

condition of progress.

Thus, in the organism which forms the basis of all modes of life,

a definite law of action is obeyed under various circumstances of

reaction with the available energy of its environment.

Similarly, in the case of the more complex leaf, we see, not only

in the phenomenon of growth, but in its extension in a flattened

form, and in the orientation of greatest surface towards the

source of energy, an attitude towards

[1] However, "In no way comparable with death." Weismann,

_Biological Memoirs_, p. 158.

68

available energy causative of accelerated transfer. There is

seemingly a principle at work, leading to the increase of organic

activity.

Many other examples might be adduced. The gastrula stage in the

development of embryos, where by invagination such an arrangement

of the multiplying cells is secured as to offer the greatest

possible surface consistent with a first division of labour; the

provision of cilia for drawing upon the energy supplies of the

medium; and more generally the specialisation of organs in the

higher developments of life, may alike be regarded as efforts of

the organism directed to the absorption of energy. When any

particular organ becomes unavailing in the obtainment of

supplies, the organ in the course of time becomes aborted or

disappears.[1] On the other hand, when a too ready and liberal

supply renders exertion and specialisation unnecessary, a similar

abortion of functionless organs takes place. This is seen in the

degraded members of certain parasites.

During certain epochs of geological history, the vegetable world

developed enormously; in response probably to liberal supplies of

carbon dioxide. A structural adaptation to the rich atmosphere

occurred, such as was calculated to cooperate in rapidly

consuming the supplies, and to this obedience to a law of

progressive transfer of energy we owe the vast stores of energy

now accumulated

[1] Claus, _Zoology_, p. 157

69

in our coal fields. And when, further, we reflect that this store

of energy had long since been dissipated into space but for the

intervention of the organism, we see definitely another factor in

organic transfer of energy—a factor acting conservatively of

energy, or antagonistically to dissipation.

The tendency of organized nature in the presence of unlimited

supplies is to "run riot." This seems so universal a relation,

that we are safe in seeing here cause and effect, and in drawing

our conclusions as to the attitude of the organism towards

available energy. New species, when they come on the field of

geological history, armed with fresh adaptations, irresistible

till the slow defences of the subjected organisms are completed,

attain enormous sizes under the stimulus of abundant supply, till

finally, the environment, living and dead, reacts upon them with

restraining influence. The exuberance of the organism in presence

of energy is often so abundant as to lead by deprivation to its

self-destruction. Thus the growth of bacteria is often controlled

by their own waste products. A moment's consideration shows that

such progressive activity denotes an accelerative attitude on the

part of the organism towards the transfer of energy into the

organic material system. Finally, we are conscious in ourselves

how, by use, our faculties are developed; and it is apparent that

all such progressive developments must rest on actions which

respond to supplies with fresh demands. Possibly in the present

and ever-

70

increasing consumption of inanimate power by civilised races, we

see revealed the dynamic attitude of the organism working through

thought-processes.

Whether this be so or not, we find generally in organised nature

causes at work which in some way lead to a progressive transfer

of energy into the organic system. And we notice, too, that all

is not spent, but both immediately in the growth of the

individual, and ultimately in the multiplication of the species,

there are actions associated with vitality which retard the

dissipation of energy. We proceed to state the dynamical

principles involved in these manifestations, which appear

characteristic of the organism, as follows:—

_The transfer of energy into any animate material system is

attended by effects conducive to the transfer, and retardative of

dissipation._

This statement is, I think, perfectly general. It has been in

part advanced before, but from the organic more than the physical

point of view. Thus, "hunger is an essential characteristic of

living matter"; and again, "hunger is a dominant characteristic

of living matter,"[1] are, in part, expressions of the statement.

If it be objected against the generality of the statement, that

there are periods in the life of individuals when stagnation and

decay make their appearance, we may answer, that

[1] _Evolution of Sex._ Geddes and Thomson, chap. xvi. See also a

reference to Cope's theory of "Growth Force," in Wallace's

_Darwinism_, p. 425.

71

such phenomena arise in phases of life developed under conditions

of external constraint, as will be urged more fully further on,

and that in fact the special conditions of old age do not and

cannot express the true law and tendency of the dynamic relations

of life in the face of its evident advance upon the Earth. The

law of the unconstrained cell is growth on an ever increasing

scale; and although we assume the organic configuration, whether

somatic or reproductive, to be essentially unstable, so that

continual inflow of energy is required merely to keep it in

existence, this does not vitiate the fact that, when free of all

external constraint, growth gains on waste. Indeed, even in the

case of old age, the statement remains essentially true, for the

phenomena then displayed point to a breakdown of the functioning

power of the cell, an approximation to configurations incapable

of assimilation. It is not as if life showed in these phenomena

that its conditions could obtain in the midst of abundance, and

yet its law be suspended; but as if they represented a

degradation of the very conditions of life, a break up, under the

laws of the inanimate, of the animate contrivance; so that energy

is no longer available to it, or the primary condition, "the

transfer of energy into the animate system," is imperfectly

obeyed. It is to the perfect contrivance of life our statement

refers.

That the final end of all will be general non-availability there

seems little reason to doubt, and the organism, itself dependent

upon differences of potential, cannot

72

hope to carry on aggregation of energy beyond the period when

differences of potential are not. The organism is not accountable

for this. It is being affected by events external to it, by the

actions going on through inanimate agents. And although there be

only a part of the received energy preserved, there is a part

preserved, and this amount is continually on the increase. To see

this it is only necessary to reflect that the sum of animate

energy—capability of doing work in any way through animate

means—at present upon the Earth, is the result, although a small

one, of energy reaching the Earth since a remote period, and

which otherwise had been dissipated in space. In inanimate

actions throughout nature, as we know it, the availability is

continually diminishing. The change is all the one way. As,

however, the supply of available energy in the universe is

(probably) limited in amount, we must look upon the two as simply

effecting the final dissipation of potential in very different

ways. The animate system is aggressive on the energy available to

it, spends with economy, and invests at interest till death

finally deprives it of all. It has heirs, indeed, who inherit

some of its gains, but they, too, must die, and ultimately there

will be no successors, and the greater part must melt away as if

it had never been. The inanimate system responds to the forces

imposed upon it by sluggish changes; of that which is thrust upon

it, it squanders uselessly. The path of the energy is very

different in the two cases.

73

While it is true generally that both systems ultimately result in

the dissipation of energy to uniform potential, the organism can,

as we have seen, under particular circumstances evade the final

doom altogether. It can lay up a store of potential energy which

may be permanent. Thus, so long as there is free oxygen in the

universe, our coalfields might, at any time in the remote future,

generate light and heat in the universal grave.

It is necessary to observe on the fundamental distinction between

the growth of the protoplasm and the growth of the crystal. It is

common to draw comparison between the two, and to point to

metabolism as the chief distinction. But while this is the most

obvious distinction the more fundamental one remains in the

energy relations of the two with the environment.[1] The growth

of the crystal is the result of loss of energy; that of the

organism the result of gain of energy. The crystal represents a

last position of stable equilibrium assumed by molecules upon a

certain loss of kinetic energy, and the formation of the crystal

by evaporation and concentration of a liquid does not, in its

dynamic aspect, differ much from the precipitation of an

amorphous sediment. The organism, on the other hand, represents a

more or less unstable condition formed and maintained by inflow

of energy; its formation, indeed, often attended with a loss of

kinetic energy (fixation of carbon in plants), but, if so,

accompanied by

[1] It appears exceptional for the crystal line configuration to

stand higher in the scale of energy than the amorphous.

74

a more than compensatory increase of potential molecular energy.

Thus, between growth in the living world and growth in the dead

world, the energy relations with the environment reveal a marked

contrast. Again, in the phenomena of combustion, there are

certain superficial resemblances which have led to comparison

between the two. Here again, however, the attitudes towards the

energy of the environment stand very much as + and -. The life

absorbs, stores, and spends with economy. The flame only

recklessly spends. The property of storage by the organism calls

out a further distinction between the course of the two

processes. It secures that the chemical activity of the organism

can be propagated in a medium in which the supply of energy is

discontinuous or localised. The chemical activity of the

combustion can, strictly speaking, only be propagated among

contiguous particles. I need not dwell on the latter fact; an

example of the former is seen in the action of the roots of

plants, which will often traverse a barren place or circumvent an

obstacle in their search for energy. In this manner roots will

find out spots of rich nutriment.

Thus there is a dynamic distinction between the progress of the

organism and the progress of the combustion, or of the chemical

reaction generally. And although there be unstable chemical

systems which absorb energy during reaction, these are

(dynamically) no more than the expansion of the compressed gas.

There is a certain

75

initial capacity in the system for a given quantity of energy;

this satisfied, progress ceases. The progress of the organism in

time is continual, and goes on from less to greater so long as

its development is unconstrained and the supply of energy is

unlimited.

We must regard the organism as a configuration which is so

contrived as to evade the tendency of the universal laws of

nature. Except we are prepared to believe that a violation of the

second law of thermodynamics occurs in the organism, that a

"sorting demon" is at work within it, we must, I think, assume

that the interactions going on among its molecules are

accompanied by retardation and dissipation like the rest of

nature. That such conditions are not incompatible with the

definition of the dynamic attitude of the organism, can be shown

by analogy with our inanimate machines which, by aid of

hypotheses in keeping with the second law of thermodynamics, may

be supposed to fulfil the energy-functions of the plant or

animal, and, in fact, in all apparent respects conform to the

definition of the organism.

We may assume this accomplished by a contrivance of the nature of

a steam-engine, driven by solar energy. It has a boiler, which we

may suppose fed by the action of the engine. It has piston,

cranks, and other movable parts, all subject to resistance from

friction, etc. Now there is no reason why this engine should not

expend its surplus energy in shaping, fitting, and starting into

action other engines:—in fact, in reproductive sacrifice. All

76

these other engines represent a multiplied absorption of energy

as the effects of the energy received by the parent engine, and

may in time be supposed to reproduce themselves. Further, we may

suppose the parent engine to be small and capable of developing

very little power, but the whole series as increasing in power at

each generation. Thus the primary energy relations of the

vegetable organism are represented in these engines, and no

violation of the second law of thermodynamics involved.

We might extend the analogy, and assuming these engines to spend

a portion of their surplus energy in doing work against chemical

forces—as, for example, by decomposing water through the

intervention of a dynamo—suppose them to lay up in this way a

store of potential energy capable of heating the boilers of a

second order of engines, representing the graminivorous animal.

It is obvious without proceeding to a tertiary or carnivorous

order, that the condition of energy in the animal world may be

supposed fulfilled in these successive series of engines, and no

violation of the principles governing the actions going on in our

machines assumed. Organisms evolving on similar principles would

experience loss at every transfer. Thus only a portion of the

radiant energy absorbed by the leaf would be expended in actual

work, chemical and gravitational, etc. It is very certain that

this is, in fact, what takes place.

It is, perhaps, worth passing observation that, from the

nutritive dependence of the animal upon the vegetable,

77

and the fact that a conversion of the energy of the one to the

purposes of the other cannot occur without loss, the mean energy

absorbed daily by the vegetable for the purpose of growth must

greatly exceed that used in animal growth; so that the chemical

potential energy of vegetation upon the earth is much greater

than the energy of all kinds represented in the animal

configurations.[1] It appears, too, that in the power possessed

by the vegetable of remaining comparatively inactive, of

surviving hard times by the expenditure and absorption of but

little, the vegetable constitutes a veritable reservoir for the

uniform supply of the more unstable and active animal.

Finally, on the question of the manner of origin of organic

systems, it is to be observed that, while the life of the present

is very surely the survival of the fittest of the tendencies and

chances of the past, yet, in the initiation of the organised

world, a single chance may have decided a whole course of events:

for, once originated, its own law secures its increase, although

within the new order of actions, the law of the fittest must

assert itself. That such a progressive material system as an

organism was possible, and at some remote period was initiated,

is matter of knowledge; whether or not the initiatory living

configuration was rare and fortuitous, or the probable result of

the general action of physical laws acting among innumerable

chances, must remain matter of

[1] I find a similar conclusion arrived at in Semper's _Animal

Life_, p. 52.

78

speculation. In the event of the former being the truth, it is

evidently possible, in spite of a large finite number of

habitable worlds, that life is non-existent elsewhere. If the

latter is the truth, it is almost certain that there is life in

all, or many of those worlds.

EVOLUTION AND ACCELERATION OF ACTIVITY

The primary factor in evolution is the "struggle for existence."

This involves a "natural selection" among the many variations of

the organism. If we seek the underlying causes of the struggle,

we find that the necessity of food and (in a lesser degree) the

desire for a mate are the principal causes of contention. The

former is much the more important factor, and, accordingly, we

find the greater degree of specialisation based upon it.

The present view assumes a dynamic necessity for its demands

involved in the nature of the organism as such. This assumption

is based on observation of the outcome of its unconstrained

growth, reproduction, and life-acts. We have the same right to

assert this of the organism as we have to assert that retardation

and degradation attend the actions of inanimate machines, which

assertion, also, is based on observation of results. Thus we pass

from the superficial statements that organisms require food in

order to live, or that organisms desire food, to the more

fundamental one that:

_The organism is a configuration of matter which absorbs energy

acceleratively, without limit, when unconstrained._

79

This is the dynamic basis for a "struggle for existence." The

organism being a material system responding to accession of

energy with fresh demands, and energy being limited in amount,

the struggle follows as a necessity. Thus, evolution guiding' the

steps of the energy-seeking organism, must presuppose and find

its origin in that inherent property of the organism which

determines its attitude in presence of available energy.

Turning to the factor, "adaptation," we find that this also must

presuppose, in order to be explicable, some quality of

aggressiveness on the part of the organism. For adaptation in

this or that direction is the result of repulse or victory, and,

therefore, we must presuppose an attack. The attack is made by

the organism in obedience to its law of demand; we see in the

adaptation of the organism but the accumulated wisdom derived

from past defeats and victories.

Where the environment is active, that is living, adaptation

occurs on both sides. Improved means of defence or improved means

of attack, both presuppose activity. Thus the reactions to the

environment, animate and inanimate, are at once the outcome of

the eternal aggressiveness of the organism, and the source of

fresh aggressiveness upon the resources of the medium.

As concerns the "survival of the fittest" (or "natural

selection"), we can, I think, at once conclude that the organism

which best fulfils the organic law under the circumstances of

supply is the "fittest," _ipso facto._ In many

80

cases this is contained in the commonsense consideration, that to

be strong, consistent with concealment from enemies which are

stronger, is best, as giving the organism mastery over foes which

are weaker, and generally renders it better able to secure

supplies. Weismann points out that natural selection favours

early and abundant reproduction. But whether the qualifications

of the "fittest" be strength, fertility, cunning, fleetness,

imitation, or concealment, we are safe in concluding that growth

and reproduction must be the primary qualities which at once

determine selection and are fostered by it. Inherent in the

nature of the organism is accelerated absorption of energy, but

the qualifications of the "fittest" are various, for the supply

of energy is limited, and there are many competitors for it. To

secure that none be wasted is ultimately the object of natural

selection, deciding among the eager competitors what is best for

each.

In short, the facts and generalisations concerning evolution must

presuppose an organism endowed with the quality of progressive

absorption of energy, and retentive of it. The continuity of

organic activity in a world where supplies are intermittent is

evidently only possible upon the latter condition. Thus it

appears that the dynamic attitude of the organism, considered in

these pages, occupies a fundamental position regarding its

evolution.

We turn to the consideration of old age and death, endeavouring

to discover in what relation they stand to the innate

progressiveness of the organism.

81

THE PERIODICITY OF THE ORGANISM AND THE LAW OF PROGRESSIVE

ACTIVITY

The organic system is essentially unstable. Its aggressive

attitude is involved in the phenomenon of growth, and in

reproduction which is a form of growth. But the energy absorbed

is not only spent in growth. It partly goes, also, to make good

the decay which arises from the instability of the organic unit.

The cell is molecularly perishable. It possesses its entity much

as a top keeps erect, by the continual inflow of energy.

Metabolism is always taking place within it. Any other condition

would, probably, involve the difficulties of perpetual motion.

The phenomenon of old age is not evident in the case of the

unicellular organism reproducing by fission. At any stage of its

history all the individuals are of the same age: all contain a

like portion of the original cell, so far as this can be regarded

as persisting where there is continual flux of matter and energy.

In the higher organisms death is universally evident. Why is

this?

The question is one of great complexity. Considered from the more

fundamental molecular point of view we should perhaps look to

failure of the power of cell division as the condition of

mortality. For it is to this phenomenon—that of cell

division—that the continued life of the protozoon is to be

ascribed, as we have already seen. Reproduction is, in fact, the

saving factor here.

As we do not know the source or nature of the stimulus

82

responsible for cell division we cannot give a molecular account

of death in the higher organisms. However we shall now see that,

philosophically, we are entitled to consider reproduction as a

saving factor in this case also; and to regard the death of the

individual much as we regard the fall of the leaf from the tree:

_i.e._ as the cessation of an outgrowth from a development

extending from the past into the future. The phenomena of old age

and natural death are, in short, not at variance with the

progressive activity of the organism. We perceive this when we

come to consider death from the evolutionary point of view.

Professor Weismann, in his two essays, "The Duration of Life,"

and "Life and Death,"[1] adopts and defends the view that "death

is not a primary necessity but that it has been secondarily

acquired by adaptation." The cell was not inherently limited in

its number of cell-generations. The low unicellular organisms are

potentially immortal, the higher multicellular forms with

well-differentiated organs contain the germs of death within

themselves.

He finds the necessity of death in its utility to the species.

Long life is a useless luxury. Early and abundant reproduction is

best for the species. An immortal individual would gradually

become injured and would be valueless or even harmful to the

species by taking the place of those that are sound. Hence

natural selection will shorten life.

[1] See his _Biological Memoirs._ Oxford, 1888.

83

Weismann contends against the transmission of acquired characters

as being unproved.[1] He bases the appearance of death on

variations in the reproductive cells, encouraged by the ceaseless

action of natural selection, which led to a differentiation into

perishable somatic cells and immortal reproductive cells. The

time-limit of any particular organism ultimately depends upon the

number of somatic cell-generations and the duration of each

generation. These quantities are "predestined in the germ itself"

which gives rise to each individual. "The existence of immortal

metazoan organisms is conceivable," but their capacity for

existence is influenced by conditions of the external world; this

renders necessary the process of adaptation. In fact, in the

differentiation of somatic from reproductive cells, material was

provided upon which natural selection could operate to shorten or

to lengthen the life of the individual in accordance with the

needs of the species. The soma is in a sense "a secondary

appendage of the real bearer of life—the reproductive cells." The

somatic cells probably lost their immortal qualities, on this

immortality becoming useless to the species. Their mortality may

have been a mere consequence of their differentiation (loc. cit.,

p. 140), itself due to natural selection. "Natural death was

not," in fact, "introduced from absolute intrinsic necessity

inherent in the nature of living matter, but on grounds of

utility,

[1] Biological Memoirs, p. 142.

84

that is from necessities which sprang up, not from the general

conditions of life, but from those special conditions which

dominate the life of multicellular organisms."

On the inherent immortality of life, Weismann finally states:

"Reproduction is, in truth, an essential attribute of living

matter, just as the growth which gives rise to it.... Life is

continuous, and not periodically interrupted: ever since its

first appearance upon the Earth in the lowest organism, it has

continued without break; the forms in which it is manifest have

alone undergone change. Every individual alive today—even the

highest—is to be derived in an unbroken line from the first and

lowest forms." [1]

At the present day the view is very prevalent that the soma of

higher organisms is, in a sense, but the carrier for a period of

the immortal reproductive cells (Ray Lankester)[2]—an appendage

due to adaptation, concerned in their supply, protection, and

transmission. And whether we regard the time-limit of its

functions as due to external constraints, recurrently acting till

their effects become hereditary, or to variations more directly

of internal origin, encouraged by natural selection, we see in

old age and death phenomena ultimately brought about in obedience

to the action of an environment. These are not inherent in the

properties of living matter. But, in spite

[1] Loc. cit., p. 159

[2] Geddes and Thomson, The Evolution of Sex, chap. xviii.

85

of its mortality, the body remains a striking manifestation of

the progressiveness of the organism, for to this it must be

ascribed. To it energy is available which is denied to the

protozoon. Ingenious adaptations to environment are more

especially its privilege. A higher manifestation, however, was

possible, and was found in the development of mind. This, too, is

a servant of the cell, as the genii of the lamp. Through it

energy is available which is denied to the body. This is the

masterpiece of the cell. Its activity dates, as it were, but from

yesterday, and today it inherits the most diverse energies of the

Earth.

Taking this view of organic succession, we may liken the

individual to a particle vibrating for a moment and then coming

to rest, but sweeping out in its motion one wave in the

continuous organic vibration travelling from the past into the

future. But as this vibration is one spreading with increased

energy from each vibrating particle, its propagation involves a

continual accelerated inflow of energy from the surrounding

medium, a dynamic condition unknown in periodic effects

transmitted by inanimate actions, and, indeed, marking the

fundamental difference between the dynamic attitudes of the

animate and inanimate.

We can trace the periodic succession of individuals on a diagram

of activity with some advantage. Considering, first, the case of

the unicellular organism reproducing by subdivision and recalling

that conditions, definite and inevitable, oppose a limit to the

rate of growth, or, for our

86

present purpose, rate of consumption of energy, we proceed as

follows:

{Fig. 1}

Along a horizontal axis units of time are measured; along a

vertical axis units of energy. Then the life-history of the

amoeba, for example, appears as a line such as A in Fig. 1.

During the earlier stages of its growth the rate of absorption of

energy is small; so that in the unit interval of time, t, the

small quantity of energy, e1, is absorbed. As life advances, the

activity of the organism augments, till finally this rate attains

a maximum, when e2 units of energy are consumed in the unit of

time.[1]

[1] Reference to p. 76, where the organic system is treated as

purely mechanical, may help readers to understand what is

involved in this curve. The solar engine may, unquestionably,

have its activity defined by such a curve. The organism is,

indeed, more complex; but neither this fact nor our ignorance of

its mechanism, affects the principles which justify the diagram.

87

On this diagram reproduction, on the part of the organism, is

represented by a line which repeats the curvature of the parent

organism originating at such a point as P in the path of the

latter, when the rate of consumption of energy has become

constant. The organism A has now ceased to act as a unit. The

products of fission each carry on the vital development of

{Fig. 2}

the species along the curve B, which may be numbered (2), to

signify that it represents the activity of two individuals, and

so on, the numbering advancing in geometrical progression. The

particular curvature adopted in the diagram is, of course,

imaginary; but it is not of an indeterminate nature. Its course

for any species is a characteristic of fundamental physical

importance, regarding the part played in nature by the particular

organism.

88

In Fig. 2 is represented the path of a primitive multicellular

organism before the effects of competition produced or fostered

its mortality. The lettering of Fig. 1 applies; the successive

reproductive acts are marked P1, P2; Q1, Q2, etc., in the paths

of the successive individuals.

{Fig. 3}

The next figure (Fig. 3) diagrammatically illustrates death in

organic history. The path ever turns more and more from the axis

of energy, till at length the point is reached when no more

energy is available; a tangent to the curve at this point is at

right angles to the axis of energy and parallel to the time axis.

The death point is reached, and however great a length we measure

along the axis of time, no further consumption of energy is

89

indicated by the path of the organism. Drawing the line beyond

the death point is meaningless for our present purpose.

It is observable that while the progress of animate nature finds

its representation on this diagram by lines sloping _upwards_ from

left to right, the course of events in inanimate nature—for

example, the history of the organic configuration after death, or

{Fig. 4}

the changes progressing—let us say, in the solar system, or in

the process of a crystallisation, would appear as lines sloping

downwards from left to right.

Whatever our views on the origin of death may be, we have to

recognise a periodicity of functions in the life-history of the

successive individuals of the present day; and whether or not we

trace this directly or indirectly to

90

a sort of interference with the rising wave of life, imposed by

the activity of a series of derived units, each seeking energy,

and in virtue of its adaptation each being more fitted to obtain

it than its predecessor, or even leave the idea of interference

out of account altogether in the origination or perpetuation of

death, the truth of the diagram (Fig. 4) holds in so far as it

may be supposed to graphically represent the dynamic history of

the individual. The point chosen on the curve for the origination

of a derived unit is only applicable to certain organisms, many

reproducing at the very close of life. A chain of units are

supposed here represented.[1]

THE LENGTH OF LIFE

If we lay out waves as above to a common scale of time for

different species, the difference of longevity is shown in the

greater or less number of vibrations executed in a given time,

_i.e._ in greater or less "frequency." We cannot indeed draw the

curvature correctly, for this would necessitate a knowledge which

we have not of the activity of the organism at different periods

of its life-history, and so neither can we plot the direction of

the organic line of propagation with respect to the

[1] Projecting upon the axes of time and energy any one complete

vibration, as in Fig. 4, the total energy consumed by the

organism during life is the length E on the axis of energy, and

its period of life is the length T on the time-axis. The mean

activity is the quotient E/T.

91

axes of reference as this involves a knowledge of the mean

activity.[1]

The group of curves which follow, relating to typical animals

possessing very different activities (Fig. 5), are therefore

entirely diagrammatic, except in respect to the approximate

{Fig. 5}

longevity of the organisms. (1) might represent an animal of the

length of life and of the activity of Man; (2), on the same scale

of longevity,

[1] In the relative food-supply at various periods of life the

curvature is approximately determinable.

92

one of the smaller mammals; and (3), the life-history of a cold

blooded animal living to a great age; _e.g._ certain of the

reptilia.

It is probable, that to conditions of structural development,

under the influence of natural selection, the question of longer

or shorter life is in a great degree referable. Thus, development

along lines of large growth will tend to a slow rate of

reproduction from the simple fact that unlimited energy to supply

abundant reproduction is not procurable, whatever we may assume

as to the strength or cunning exerted by the individual in its

efforts to obtain its supplies. On the other hand, development

along lines of small growth, in that reproduction is less costly,

will probably lead to increased rate of reproduction. It is, in

fact, matter of general observation that in the case of larger

animals the rate of reproduction is generally slower than in the

case of smaller animals. But the rate of reproduction might be

expected to have an important influence in determining the

particular periodicity of the organism. Were we to depict in the

last diagram, on the same time-scale as Man, the vibrations of

the smaller and shorter-lived living things, we would see but a

straight line, save for secular variations in activity,

representing the progress of the species in time: the tiny

thrills of its units lost in comparison with the yet brief period

of Man.

The interdependence of the rate of reproduction and

93

the duration of the individual is, indeed, very probably revealed

in the fact that short-lived animals most generally reproduce

themselves rapidly and in great abundance, and vice versa. In

many cases where this appears contradicted, it will be found that

the young are exposed to such dangers that but few survive (_e.g._

many of the reptilia, etc.), and so the rate of reproduction is

actually slow.

Death through the periodic rigour of the inanimate environment

calls forth phenomena very different from death introduced or

favoured by competition. A multiplicity of effects simulative of

death occur. Organisms will, for example, learn to meet very

rigorous conditions if slowly introduced, and not permanent. A

transitory period of want can be tided over by contrivance. The

lily withdrawing its vital forces into the bulb, protected from

the greatest extremity of rigour by seclusion in the Earth; the

trance of the hibernating animal; are instances of such

contrivances.

But there are organisms whose life-wave truly takes up the

periodicity of the Earth in its orbit. Thus the smaller animals

and plants, possessing less resources in themselves, die at the

approach of winter, propagating themselves by units which,

whether egg or seed, undergo a period of quiescence during the

season of want. In these quiescent units the energy of the

organism is potential, and the time-energy function is in

abeyance. This condition is, perhaps, foreshadowed in the

encyst-

94

ment of the amoeba in resistance to drought. In most cases of

hibernation the time-energy function seems maintained at a loss

of potential by the organism, a diminished vital consumption of

energy being carried on at the expense of the stored energy of

the tissues. So, too, even among the largest organisms there will

be a diminution of activity periodically inspired by

climatological conditions. Thus, wholly or in part, the activity

of organisms is recurrently affected by the great energy—tides

set up by the Earth's orbital motion.

{Fig. 6}

Similarly in the phenomenon of sleep the organism responds to the

Earth's axial periodicity, for in the interval of night a period

of impoverishment has to be endured. Thus the diurnal waves of

energy also meet a response in the organism. These tides and

waves of activity would appear as larger and smaller ripples

95

on the life-curve of the organism. But in some, in which life and

death are encompassed in a day, this would not be so; and for the

annual among plants, the seed rest divides the waves with lines

of no activity (Fig. 6).

Thus, finally, we regard the organism as a dynamic phenomenon

passing through periodic variations of intensity. The material

systems concerned in the transfer of the energy rise, flourish,

and fall in endless succession, like cities of ancient dynasties.

At points of similar phase upon the waves the rate of consumption

of energy is approximately the same; the functions, too, which

demand and expend the energy are of similar nature.

That the rhythm of these events is ultimately based on harmony in

the configuration and motion of the molecules within the germ

seems an unavoidable conclusion. In the life of the individual

rhythmic dynamic phenomena reappear which in some cases have no

longer a parallel in the external world, or under conditions when

the individual is no longer influenced by these external

conditions.,, In many cases the periodic phenomena ultimately die

out under new influences, like the oscillations of a body in a

viscous medium; in others when they seem to be more deeply rooted

in physiological conditions they persist.

The "length of life is dependent upon the number

[1] The _Descent of Man._

96

of generations of somatic cells which can succeed one another in

the course of a single life, and furthermore the number as well

as the duration of each single cell-generation is predestined in

the germ itself."[1]

Only in the vague conception of a harmonising or formative

structural influence derived from the germ, perishing in each

cell from internal causes, but handed from cell to cell till the

formative influence itself degrades into molecular discords, does

it seem possible to form any physical representation of the

successive events of life. The degradation of the molecular

formative influence might be supposed involved in its frequent

transference according to some such dynamic actions as occur in

inanimate nature. Thus, ultimately, to the waste within the cell,

to the presence of a force retardative of its perpetual harmonic

motions, the death of the individual is to be ascribed. Perhaps

in protoplasmic waste the existence of a universal death should

be recognised. It is here we seem to touch inanimate nature; and

we are led back to a former conclusion that the organism in its

unconstrained state is to be regarded as a contrivance for

evading the dynamic tendencies of actions in which lifeless

matter participates.[2]

[1] Weismann, _Life and Death; Biological Memoirs_, p. 146.

[2] In connection with the predestinating power and possible

complexity of the germ, it is instructive to reflect on the very

great molecular population of even the smallest spores—giving

rise to very simple forms. Thus, the spores of the unicellular

Schizomycetes are estimated to dimensions as low as 1/10,000 of a

millimetre in diameter (Cornil et Babes, _Les Batteries_, 1. 37).

From Lord Kelvin's estimate of the number of molecules in water,

comprised within the length of a wave-length of yellow light

(_The Size of Atoms_, Proc. R. I., vol. x., p. 185) it is

probable that such spores contain some 500,000 molecules, while

one hundred molecules range along a diameter.

97

THE NUMERICAL ABUNDANCE OF LIFE

We began by seeking in various manifestations of life a dynamic

principle sufficiently comprehensive to embrace its very various

phenomena. This, to all appearance, found, we have been led to

regard life, to a great extent, as a periodic dynamic phenomenon.

Fundamentally, in that characteristic of the contrivance, which

leads it to respond favourably to transfer of energy, its

enormous extension is due. It is probable that to its instability

its numerical abundance is to be traced—for this, necessitating

the continual supply of all the parts already formed, renders

large, undifferentiated growth, incompatible with the limited

supplies of the environment. These are fundamental conditions of

abundant life upon the Earth.

Although we recognise in the instability of living systems the

underlying reason for their numerical abundance, secondary

evolutionary causes are at work. The most important of these is

the self-favouring nature of the phenomenon of reproduction. Thus

there is a tendency not only to favour reproductiveness, but

early reproductiveness, in the form of one prolific

reproductive.

98

act, after which the individual dies.[1] Hence the wavelength of

the species diminishes, reproduction is more frequent, and

correspondingly greater numbers come and go in an interval of

time.

Another cause of the numerical abundance of life exists, as

already stated, in the conditions of nourishment. Energy is more

readily conveyed to the various parts of the smaller mass, and

hence the lesser organisms will more actively functionate; and

this, as being the urging dynamic attitude, as well as that most

generally favourable in the struggle, will multiply and favour

such forms of life. On the other hand, however, these forms will

have less resource within themselves, and less power of

endurance, so that they are only suitable to fairly uniform

conditions of supply; they cannot survive the long continued want

of winter, and so we have the seasonal abundance of summer. Only

the larger and more resistant organisms, whether animal or

vegetable, will, in general, populate the Earth from year to

year. From this we may conclude that, but for the seasonal

energy-tides, the development of life upon the globe had gone

along very different lines from those actually followed. It is,

indeed, possible that the evolution of the larger organisms would

not have occurred; there would have been no vacant place for

their development, and a being so endowed as Man could hardly

[1] Weismann, _The Duration of Life._

99

have been evolved. We may, too, apply this reasoning elsewhere,

and regard as highly probable, that in worlds which are without

seasonal influences, the higher developments of life have not

appeared; except they have been evolved under other conditions,

when they might for a period persist. We have, indeed, only to

picture to ourselves what the consequence of a continuance of

summer would be on insect life to arrive at an idea of the

antagonistic influences obtaining in such worlds to the survival

of larger organisms.

It appears that to the dynamic attitude of life in the first

place, and secondarily to the environmental conditions limiting

undifferentiated growth, as well as to the action of heredity in

transmitting the reproductive qualities of the parent to the

offspring, the multitudes of the pines, and the hosts of ants,

are to be ascribed. Other causes are very certainly at work, but

these, I think, must remain primary causes.

We well know that the abundance of the ants and pines is not a

tithe of the abundance around us visible and invisible. It is a

vain endeavour to realise the countless numbers of our

fellow-citizens upon the Earth; but, for our purpose, the

restless ants, and the pines solemnly quiet in the sunshine, have

served as types of animate things. In the pine the gates of the

organic have been thrown open that the vivifying river of energy

may flow in. The ants and the butterflies sip for a brief moment

of its waters, and again vanish into the

100

inorganic: life, love and death encompassed in a day.

Whether the organism stands at rest and life comes to it on the

material currents of the winds and waters, or in the vibratory

energy of the æther; or, again, whether with restless craving it

hurries hither and thither in search of it, matters nothing. The

one principle—the accelerative law which is the law of the

organic—urges all alike onward to development, reproduction and

death. But although the individual dies death is not the end; for

life is a rhythmic phenomenon. Through the passing ages the waves

of life persist: waves which change in their form and in the

frequency to which they are attuned from one geologic period to

the next, but which still ever persist and still ever increase.

And in the end the organism outlasts the generations of the

hills.

101

THE BRIGHT COLOURS OF ALPINE FLOWERS [1]

IT is admitted by all observers that many species of flowering

plants growing on the higher alps of mountainous regions display

a more vivid and richer colour in their bloom than is displayed

in the same species growing in the valleys. That this is actually

the case, and not merely an effect produced upon the observer by

the scant foliage rendering the bloom more conspicuous, has been

shown by comparative microscopic examination of the petals of

species growing on the heights and in the valleys. Such

examination has revealed that in many cases pigment granules are

more numerous in the individuals growing at the higher altitudes.

The difference is specially marked in Myosotis sylvatica,

Campanula rotundifolia, Ranunculus sylvaticus, Galium cruciatum,

and others. It is less marked in the case of Thymus serpyllum and

Geranium sylvaticum; while in Rosa alpina and Erigeron alpinus no

difference is observable.[2]

In the following cases a difference of intensity of colour is,

according to Kerner ("Pflanzenleben," 11. 504), especially

noticeable:— _Agrostemma githago, Campanula

[1] _Proc. Royal Dublin Society_, 1893.

[2] G. Bonnier, quoted by De Varigny, _Experimental Evolution_,

p. 55.

102

pusilla, Dianthus inodorus (silvestris), Gypsophila repens, Lotus

corniculatus, Saponaria ocymoides, Satureja hortensis, Taraxacumm

officinale, Vicia cracca, and Vicia sepium._

To my own observation this beautiful phenomenon has always

appeared most obvious and impressive. It appears to have struck

many unprofessional observers. Helmholtz offers the explanation

that the vivid colours are the result of the brighter sunlight of

the heights. It has been said, too, that they are the direct

chemical effects of a more highly ozonized atmosphere. The latter

explanation I am unable to refer to its author. The following

pages contain a suggestion on the matter, which occurred to me

while touring, along with Henry H. Dixon, in the Linthal district

of Switzerland last summer.[1]

If the bloom of these higher alpine flowers is especially

pleasing to our own æsthetic instincts, and markedly conspicuous

to us as observers, why not also especially attractive and

conspicuous to the insect whose mission it is to wander from

flower to flower over the pastures? The answer to this question

involves the hypothesis I would advance as accounting for the

bright colours of high-growing individuals. In short, I believe a

satisfactory explanation is to be found in the conditions of

insect life in the higher alps.

In the higher pastures the summer begins late and

[1] The summer of 1892.

103

closes early, and even in the middle of summer the day closes in

with extreme cold, and the cold of night is only dispelled when

the sun is well up. Again, clouds cover the heights when all is

clear below, and cold winds sweep over them when there is warmth

and shelter in the valleys. With these rigorous conditions the

pollinating insects have to contend in their search for food, and

that when the rival attractions of the valleys below are so many.

I believe it is these rigorous conditions which are indirectly

responsible for the bright colours of alpine flowers. For such

conditions will bring about a comparative scarcity of insect

activity on the heights; and a scarcity or uncertainty in the

action of insect agency in effecting fertilization will intensify

the competition to attract attention, and only the brightest

blooms will be fertilized.[1]

This will be a natural selection of the brightest, or the

[1] Grant Allen, I have recently learned, advances in _Science in

Arcady_ the theory that there is a natural selective cause

fostering the bright blooms of alpines. The selective cause is,

however, by him referred to the greater abundance of butterfly

relatively to bee fertilizers. The former, he says, display more

æsthetic instinct than bees. In the valley the bees secure the

fertilization of all. I may observe that upon the Fridolins Alp

all the fertilizers we observed were bees. I have always found

butterflies very scarce at altitudes of 7,000 to 8,000 feet. The

alpine bees are very light in body, like our hive bee, and I do

not think rarefaction of the atmosphere can operate to hinder its

ascent to the heights, as Grant Allen suggests. The observations

on the death-rate of bees and butterflies on the glacier, to be

referred to presently, seem to negative such a hypothesis, and to

show that a large preponderance of bees over butterflies make

their way to the heights.

104

brightest will be the fittest, and this condition, along with the

influence of heredity, will encourage a race of vivid flowers. On

the other hand, the more scant and uncertain root supply, and the

severe atmospheric conditions, will not encourage the grosser

struggle for existence which in the valleys is carried on so

eagerly between leaves and branches—the normal offensive and

defensive weapons of the plant—and so the struggle becomes

refined into the more æsthetic one of colour and brightness

between flower and flower. Hence the scant foliage and vivid

bloom would be at once the result of a necessary economy, and a

resort to the best method of securing reproduction under the

circumstances of insect fertilizing agency. Or, in other words,

while the luxuriant growth is forbidden by the conditions, and

thus methods of offence and defence, based upon vigorous

development, reduced in importance, it would appear that the

struggle is mainly referred to rivalry for insect preference. It

is probable that this is the more economical manner of carrying

on the contest.

In the valleys we see on every side the struggle between the

vegetative organs of the plant; the soundless battle among the

leaves and branches. The blossom here is carried aloft on a

slender stem, or else, taking but a secondary part in the

contest, it is relegated to obscurity (P1. XII.). Further up on

the mountains, where the conditions are more severe and the

supplies less abundant, the leaf and branch assume lesser

dimensions, for they are costly weapons to provide and the

elements are unfriendly

105

to their existence (Pl. XIII.). Still higher, approaching the

climatic limit of vegetable life, the struggle for existence is

mainly carried on by the æsthetic rivalry of lowly but

conspicuous blossoms.

As regards the conditions of insect life in the higher alps, it

came to my notice in a very striking manner that vast numbers of

such bees and butterflies as venture up perish in the cold of

night time. It appears as if at the approach of dusk these are

attracted by the gleam of the snow, and quitting the pastures,

lose themselves upon the glaciers and firns, there to die in

hundreds. Thus in an ascent of the Tödi from the Fridolinshüte we

counted in the early dawn sixty-seven frozen bees, twenty-nine

dead butterflies, and some half-dozen moths on the Biferten

Glacier and Firn. These numbers, it is to be remembered, only

included those lying to either side of our way over the snow, so

that the number must have mounted up to thousands when integrated

over the entire glacier and firn. Approaching the summit none

were found. The bees resembled our hive bee in appearance, the

butterflies resembled the small white variety common in our

gardens, which has yellow and black upon its wings. One large

moth, striped across the abdomen, and measuring nearly two inches

in length of body, was found. Upon our return, long after the

sun's rays had grown strong, we observed some of the butterflies

showed signs of reanimation. We descended so quickly to avoid the

inconvenience of the soft snow that we had time for no

106

close observation on the frozen bees. But dead bees are common

objects upon the snows of the alps.

These remarks I noted down roughly while at Linthal last summer,

but quite recently I read in Natural Science[1] the following

note:

"Late Flowering Plants.—While we write, the ivy is in flower, and

bees, wasps, and flies are jostling each other and struggling to

find standing-room on the sweet-smelling plant. How great must be

the advantage obtained by this plant through its exceptional

habit of flowering in the late autumn, and ripening its fruit in

the spring. To anyone who has watched the struggle to approach

the ivy-blossom at a time when nearly all other plants are bare,

it is evident that, as far as transport of pollen and

cross-fertilization go, the plant could not flower at a more

suitable time. The season is so late that most other plants are

out of flower, but yet it is not too late for many insects to be

brought out by each sunny day, and each insect, judging by its

behaviour, must be exceptionally hungry.

"Not only has the ivy the world to itself during its flowering

season, but it delays to ripen its seed till the spring, a time

when most other plants have shed their seed, and most edible

fruits have been picked by the birds. Thus birds wanting fruit in

the spring can obtain little but ivy, and how they appreciate the

ivy berry is evident

[1] For December, 1892, vol. i., p. 730.

107

by the purple stains everywhere visible within a short distance

of the bush."

These remarks suggest that the ivy adopts the converse attitude

towards its visitors to that forced upon the alpine flower. The

ivy bloom is small and inconspicuous, but then it has the season

to itself, and its inconspicuousness is no disadvantage, _i.e._

if one plant was more conspicuous than its neighbours, it would

not have any decided advantage where the pollinating insect is

abundant and otherwise unprovided for. Its dark-green berries in

spring, which I would describe as very inconspicuous, have a

similar advantage in relation to the necessities of bird life.

The experiments of M. C. Flahault must be noticed. This

naturalist grew seeds of coloured flowers which had ripened in

Paris, part in Upsala, and part in Paris; and seed which had

ripened in Upsala, part at Paris, and part at Upsala. The flowers

opening in the more northern city were in most cases the

brighter.[1] If this observation may be considered indisputable,

as appears to be the case, the question arises, Are we to regard

this as a direct effect of the more rigorous climate upon the

development of colouring matter on the blooms opening at Upsala?

If we suppose an affirmative answer, the theory of direct effect

by sun brightness must I think be abandoned. But I venture to

think that the explanation of the Upsala

[1] Quoted by De Varigny, _Experimental Evolution_, p. 56.

108

experiment is not to be found in direct climatic influence upon

the colour, but in causes which lie deeper, and involve some

factors deducible from biological theory.

The organism, as a result of the great facts of heredity and of

the survival of the fittest, is necessarily a system which

gathers experience with successive generations; and the principal

lesson ever being impressed upon it by external events is

economy. Its success depends upon the use it makes of its

opportunities for the reception of energy and the economy

attained in disposing of what is gained.

With regard to using the passing opportunity the entire seasonal

development of life is a manifestation of this attitude, and the

fleetness, agility, etc., of higher organisms are developments in

this direction. The higher vegetable organism is not locomotory,

save in the transferences of pollen and seed, for its food comes

to it, and the necessary relative motion between food and

organism is preserved in the quick motion of radiated energy from

the sun and the slower motion of the winds on the surface of the

earth. But, even so, the vegetable organism must stand ever ready

and waiting for its supplies. Its molecular parts must be ready

to seize the prey offered to it, somewhat as the waiting spider

the fly. Hence, the plant stands ready; and every cloud with

moving shadow crossing the fields handicaps the shaded to the

benefit of the unshaded plant in the adjoining field. The open

bloom

109

is a manifestation of the generally expectant attitude of the

plant, but in relation to reproduction.

As regards economy, any principle of maximum economy, where many

functions have to be fulfilled, will, we may very safely predict,

involve as far as possible mutual helpfulness in the processes

going on. Thus the process of the development towards meeting any

particular external conditions, A, suppose, will, if possible,

tend to forward the development towards meeting conditions B; so

that, in short, where circumstances of morphology and physiology

are favourable, the ideally economical system will be attained

when in place of two separate processes, a, ß, the one process y,

cheaper than a + ß, suffices to advance development

simultaneously in both the directions A and B. The economy is as

obvious as that involved in "killing two birds with the one

stone"—if so crude a simile is permissible—and it is to be

expected that to foster such economy will be the tendency of

evolution in all organic systems subjected to restraints as those

we are acquainted with invariably are.

Such economy might be simply illustrated by considering the case

of a reservoir of water elevated above two hydraulic motors, so

that the elevated mass of water possessed gravitational

potential. The available energy here represents the stored-up

energy in the organism. How best may the water be conveyed to the

two motors [the organic systems reacting towards conditions A and

B] so

110

that as little energy as possible is lost in transit? If the

motors are near together it is most economical to use the one

conduit, which will distribute the requisite supply of water to

both. If the motors are located far asunder it will be most

economical to lay separate conduits. There is greatest economy in

meeting a plurality of functions by the same train of

physiological processes where this is consistent with meeting

other demands necessitated by external or internal conditions.

But an important and obvious consequence arises in the supply of

the two motors from the one conduit. We cannot work one motor

without working the other. If we open a valve in the conduit both

motors start into motion and begin consuming the energy stored in

the tank. And although they may both under one set of conditions

be doing useful and necessary work, in some other set of

conditions it may be needless for both to be driven.

This last fact is an illustration of a consideration which must

enter into the phenomenon which an eminent biologist speaks of as

physiological or unconscious "memory,"[1] For the development of

the organism from the ovum is but the starting of a train of

interdependent events of a complexity depending upon the

experience of the past.

[1] Ewald Hering, quoted by Ray Lankaster, _The Advancement of

Science_, p. 283.

111

In short, we may suppose the entire development of the plant,

towards meeting certain groups of external conditions,

physiologically knit together according as Nature tends to

associate certain groups of conditions. Thus, in the case in

point, climatic rigour and scarcity of pollinating agency will

ever be associated; and in the long experience of the past the

most economical physiological attitude towards both is, we may

suppose, adopted; so that the presence of one condition excites

the apparent unconscious memory of the other. In reality the

process of meeting the one condition involves the process and

development for meeting the other.

And this consideration may be extended very generally to such

organisms as can survive under the same associated natural

conditions, for the history of evolution is so long, and the

power of locomotion so essential to the organism at some period

in its life history, that we cannot philosophically assume a

local history for members of a species even if widely severed

geographically at the present day. At some period in the past

then, it is very possible that the individuals today thriving at

Paris, acquired the experience called out at Upsala. The

perfection of physiological memory inspires no limit to the date

at which this may have occurred—possibly the result of a

succession of severe seasons at Paris; possibly the result of

migrations —and the seed of many flowering plants possess means

of migration only inferior to those possessed by the flying and

swimming animals. But, again, possibly the experi-

112

ence was acquired far back in the evolutionary history of the

flower.[1]

But a further consideration arises. Not only at each moment in

the life of the individual must maximum income and most judicious

expenditure be considered, but in its whole life history, and

even over the history of its race, the efficiency must tend to be

a maximum. This principle is even carried so far that when

necessary it leads to the death of the individual, as in the case

of those organisms which, having accomplished the reproductive

act, almost immediately expire. This view of nature may be

repellent, but it is, nevertheless, evident that we are parts of

a system which ruthlessly sacrifices the individual on general

grounds of economy. Thus, if the curve which defines the mean

rate of reception of energy of all kinds at different periods in

the life of the organism be opposed by a second curve, drawn

below the axis along which time is measured, representing the

mean rate of expenditure of energy on development, reproduction,

etc. (Fig. 7), this latter curve, which is, of course,

[1] The blooms of self-fertilising, and especially of

cleistogamic plants (_e.g._ Viola), are examples of unconscious

memory, or unconscious "association of ideas" leading to the

development of organs now functionless. The _Pontederia crassipes_

of the Amazon, which develops its floating bladders when grown in

water, but aborts them rapidly when grown on land, and seems to

retain this power of adaptation to the environment for an

indefinite period of time, must act in each case upon an

unconscious memory based upon past experience. Many other cases

might be cited.

113

physiologically dependent on the former, must be of such a nature

from its origin to its completion in death, that the condition is

realized of the most economical rate of expenditure at each

period of life.[1] The rate of expenditure of energy at any

period of life is, of course, in such a curve defined by the

slope of the curve towards the axis of time at the period in

question; but this particular slope _must be led to by a previous

part of the curve, and involves its past and future course to a

very great extent_.

{Fig. 7}

There will, therefore, be impressed upon the

organism by the factors of evolution a unified course of

economical expenditure completed only by its death, and which

will give to the developmental progress of the individual its

prophetic character.

In this way we look to the unified career of each organic unit,

from its commencement in the ovum to the day

[1] See _The Abundance of Life_.

114

when it is done with vitality, for that preparation for momentous

organic events which is in progress throughout the entire course

of development; and to the economy involved in the welding of

physiological processes for the phenomenon of physiological

memory, wherein we see reflected, as it were, in the development

of the organism, the association of inorganic restraints

occurring in nature which at some previous period impressed

itself upon the plastic organism. We may picture the seedling at

Upsala, swayed by organic memory and the inherited tendency to an

economical preparation for future events, gradually developing

towards the æsthetic climax of its career. In some such manner

only does it appear possible to account for the prophetic

development of organisms, not alone to be observed in the alpine

flowers, but throughout nature.

And thus, finally, to the effects of natural selection and to

actions defined by general principles involved in biology, I

would refer for explanation of the manner in which flowers on the

Alps develop their peculiar beauty.

115

MOUNTAIN GENESIS

OUR ancestors regarded mountainous regions with feelings of

horror, mingled with commiseration for those whom an unkindly

destiny had condemned to dwell therein. We, on the other hand,

find in the contemplation of the great alps of the Earth such

peaceful and elevated thoughts, and such rest to our souls, that

it is to those very solitudes we turn to heal the wounds of ife.

It is difficult to explain the cause of this very different point

of view. It is probably, in part, to be referred to that cloud of

superstitious horror which, throughout the Middle Ages, peopled

the solitudes with unknown terrors; and, in part, to the

asceticism which led the pious to regard the beauty and joy of

life as snares to the soul's well-being. In those eternal

solitudes where the overwhelming forces of Nature are most in

evidence, an evil principle must dwell or a dragon's dreadful

brood must find a home.

But while in our time the aesthetic aspect of the hills appeals

to all, there remains in the physical history of the mountains

much that is lost to those who have not shared in the scientific

studies of alpine structure and genesis. They lose a past history

which for interest com-

116

petes with anything science has to tell of the changes of the

Earth.

Great as are the physical features of the mountains compared with

the works of Man, and great as are the forces involved compared

with those we can originate or control, the loftiest ranges are

small contrasted with the dimensions of the Earth. It is well to

bear this in mind. I give here (Pl. XV.) a measured drawing

showing a sector cut from a sphere of 50 cms. radius; so much of

it as to exhibit the convergence of its radial boundaries which

if prolonged will meet at the centre. On the same scale as the

radius the diagram shows the highest mountains and the deepest

ocean. The average height of the land and the average depth of

the ocean are also exhibited. We see how small a movement of the

crust the loftiest elevation of the Himalaya represents and what

a little depression holds the ocean.

Nevertheless, it is not by any means easy to explain the genesis

of those small elevations and depressions. It would lead us far

from our immediate subject to discuss the various theoretical

views which have been advanced to account for the facts. The idea

that mountain folds, and the lesser rugosities of the Earth's

surface, arose in a wrinkling of the crust under the influence of

cooling and skrinkage of the subcrustal materials, is held by

many eminent geologists, but not without dissent from others.

The most striking observational fact connected with mountain

structure is that, without exception, the ranges

117

of the Earth are built essentially of sedimentary rocks: that is

of rocks which have been accumulated at some remote past time

beneath the surface of the ocean. A volcanic core there may

sometimes be—probably an attendant or consequence of the

uplifting—or a core of plutonic igneous rocks which has arisen

under the same compressive forces which have bowed and arched the

strata from their original horizontal position. It is not

uncommon to meet among unobservant people those who regard all

mountain ranges as volcanic in origin. Volcanoes, however, do not

build mountain ranges. They break out as more or less isolated

cones or hills. Compare the map of the Auvergne with that of

Switzerland; the volcanoes of South Italy with the Apennines.

Such great ranges as those which border with triple walls the

west coast of North America are in no sense volcanic: nor are the

Pyrenees, the Caucasus, or the Himalaya. Volcanic materials are

poured out from the summits of the Andes, but the range itself is

built up of folded sediments on the same architecture as the

other great ranges of the Earth.

Before attempting an explanation of the origin of the mountains

we must first become more closely acquainted with the phenomena

attending mountain elevation.

At the present day great accumulations of sediment are taking

place along the margins of the continents where the rivers reach

the ocean. Thus, the Gulf of Mexico receiving the sediment of the

Mississippi and Rio Grande;

118

the northeast coast of South America receiving the sediments of

the Amazons; the east coast of Asia receiving the detritus of the

Chinese rivers; are instances of such areas of deposition. Year

by year, century by century, the accumulation progresses, and as

it grows the floor of the sea sinks under the load. Of the

yielding of the crust under the burthen of the sediments we are

assured; for otherwise the many miles of vertically piled strata

which are uplifted to our view in the mountains, never could have

been deposited in the coastal seas of the past. The flexure and

sinking of the crust are undeniable realities.

Such vast subsiding areas are known as geosynclines. From the

accumulated sediments of the geosynclines the mountain ranges of

the past have in every case originated; and the mountains of the

future will assuredly arise and lofty ranges will stand where now

the ocean waters close over the collecting sediments. Every

mountain range upon the Earth enforces the certainty of this

prediction.

The mountain-forming movement takes place after a certain great

depth of sediment is collected. It is most intense where the

thickness of deposit is greatest. We see this when we examine the

structure of our existing mountain ranges. At either side where

the sediments thin out, the disturbance dies away, till we find

the comparatively shallow and undisturbed level sediments which

clothe the continental surface.

Whatever be the connection between the deposition and

119

the subsequent upheaval, _the element of great depth of

accumulation seems a necessary condition and must evidently enter

as a factor into the Physical Processes involved_. The mountain

range can only arise where the geosyncline is deeply filled by

long ages of sedimentation.

Dana's description of the events attending mountain building is

impressive:

"A mountain range of the common type, like that to which the

Appalachians belong, is made out of the sedimentary formations of

a long preceding era; beds that were laid down conformably, and

in succession, until they had reached the needed thickness; beds

spreading over a region tens of thousands of square miles in

area. The region over which sedimentary formations were in

progress in order to make, finally, the Appalachian range,

reached from New York to Alabama, and had a breadth of 100 to 200

miles, and the pile of horizontal beds along the middle was

40,000 feet in depth. The pile for the Wahsatch Mountains was

60,000 feet thick, according to King. The beds for the

Appalachians were not laid down in a deep ocean, but in shallow

waters, where a gradual subsidence was in progress; and they at

last, when ready for the genesis, lay in a trough 40,000 feet

deep, filling the trough to the brim. It thus appears that epochs

of mountain-making have occurred only after long intervals of

quiet in the history of a continent."[1]

[1] Dana, _Manual of Geology_, third edition, p. 794

120

On the western side of North America the work of

mountain-building was, indeed, on the grandest scale. For long

ages and through a succession of geological epochs, sedimentation

had proceeded so that the accumulations of Palaeozoic and

Mesozoic times had collected in the geosyncline formed by their

own ever increasing weight. The site of the future Laramide range

was in late Cretaceous times occupied by some 50,000 feet of

sedimentary deposits; but the limit had apparently been attained,

and at this time the Laramide range, as well as its southerly

continuation into the United States, the Rockies, had their

beginning. Chamberlin and Salisbury[1] estimate that the height

of the mountains developed in the Laramide range at this time was

20,000 feet, and that, owing to the further elevation which has

since taken place, from 32,000 to 35,000 feet would be their

present height if erosion had not reduced them. Thus on either

side of the American continent we have the same forces at work,

throwing up mountain ridges where the sediments had formerly been

shed into the ocean.

These great events are of a rhythmic character; the crust, as it

were, pulsating under the combined influences of sedimentation

and denudation. The first involves downward movements under a

gathering load, and ultimately a reversal of the movement to one

of upheaval; the second factor, which throughout has been in

[1] Chamberlin and Salisbury, _Geology_, 1906, iii., 163.

121

operation as creator of the sediments, then intervenes as an

assailant of the newly-raised mountains, transporting their

materials again to the ocean, when the rhythmic action is

restored to its first phase, and the age-long sequence of events

must begin all over again.

It has long been inferred that compressive stress in the crust

must be a primary condition of these movements. The wvork

required to effect the upheavals must be derived from some

preexisting source of energy. The phenomenon—intrinsically one of

folding of the crust—suggests the adjustment of the earth-crust

to a lessening radius; the fact that great mountain-building

movements have simultaneously affected the entire earth is

certainly in favour of the view that a generally prevailing cause

is at the basis of the phenomenon.

The compressive stresses must be confined to the upper few miles

of the crust, for, in fact, the downward increase of temperature

and pressure soon confers fluid properties on the medium, and

slow tangential compression results in hydrostatic pressure

rather than directed stresses. Thus the folding visible in the

mountain range, and the lateral compression arising therefrom,

are effects confined to the upper parts of the crust.

The energy which uplifts the mountain is probably a surviving

part of the original gravitational potential energy of the crust

itself. It must be assumed that the crust in following downwards

the shrinking subcrustal magma, develops immense compressive

stresses in

122

its materials, vast geographical areas being involved. When

folding at length takes place along the axis of the elongated

syncline of deposition, the stresses find relief probably for

some hundreds of miles, and the region of folding now becomes

compressed in a transverse direction. As an illustration, the

Laramide range, according to Dawson, represents the reduction of

a surface-belt 50 miles wide to one of 25 miles. The marvellous

translatory movements of crustal folds from south to north

arising in the genesis of the Swiss Alps, which recent research

has brought to light, is another example of these movements of

relief, which continue to take place perhaps for many millions of

years after they are initiated.

The result of this yielding of the crust is a buckling of the

surface which on the whole is directed upwards; but depression

also is an attendant, in many cases at least, on mountain

upheaval. Thus we find that the ocean floor is depressed into a

syncline along the western coast of South America; a trough

always parallel to the ranges of the Andes. The downward

deflection of the crust is of course an outcome of the same

compressive stresses which elevate the mountain.

The fact that the yielding of the crust is always situated where

the sediments have accumulated to the greatest depth, has led to

attempts from time to time of establishing a physical connexion

between the one and the other. The best-known of these theories

is that of Babbage and Herschel. This seeks the connexion in the

rise of the

123

geotherms into the sinking mass of sediment and the consequent

increase of temperature of the earth-crust beneath. It will be

understood that as these isogeotherms, or levels at which the

temperature is the same, lie at a uniform distance from the

surface all over the Earth, unless where special variations of

conductivity may disturb them, the introduction of material

pressed downwards from above must result in these materials

partaking of the temperature proper to the depth to which they

are depressed. In other words the geotherms rise into the sinking

sediments, always, however, preserving their former average

distance from the surface. The argument is that as this process

undoubtedly involves the heating up of that portion of the crust

which the sediments have displaced downwards, the result must be

a local enfeeblement of the crust, and hence these areas become

those of least resistance to the stresses in the crust.

When this theory is examined closely, we see that it only amounts

to saying that the bedded rocks, which have taken the place of

the igneous materials beneath, as a part of the rigid crust of

the Earth, must be less able to withstand compressive stress than

the average crust. For there has been no absolute rise of the

geotherms, the thermal conductivities of both classes of

materials differing but little. Sedimentary rock has merely taken

the place of average crust-rock, and is subjected to the same

average temperature and pressure prevailing in the surrounding

crust. But are there any grounds for the

124

assumption that the compressive resistance of a complex of

sedimentary rocks is inferior to one of igneous materials? The

metamorphosed siliceous sediments are among the strongest rocks

known as regards resistance to compressive stress; and if

limestones have indeed plastic qualities, it must be remembered

that their average amount is only some 5 per cent. of the whole.

Again, so far as rise of temperature in the upper crust may

affect the question, a temperature which will soften an average

igneous rock will not soften a sedimentary rock, for the reason

that the effect of solvent denudation has been to remove those

alkaline silicates which confer fusibility.

When, however, we take into account the radioactive content of

the sediments the matter assumes a different aspect.

The facts as to the general distribution of radioactive

substances at the surface, and in rocks which have come from

considerable depths in the crust, lead us to regard as certain

the widespread existence of heat-producing radioactive elements

in the exterior crust of the Earth. We find, indeed, in this fact

an explanation—at least in part—of the outflow of heat

continually taking place at the surface as revealed by the rising

temperature inwards. And we conclude that there must be a

thickness of crust amounting to some miles, containing the

radioactive elements.

Some of the most recent measurements of the quantities of radium

and thorium in the rocks of igneous origin—_e.g._ granites,

syenites, diorites, basalts, etc., show that the

125

radioactive heat continually given out by such rocks amounts to

about one millionth part of 0.6 calories per second per cubic

metre of average igneous rock. As we have to account for the

escape of about 0.0014 calorie[1] per square metre of the Earth's

surface per second (assuming the rise of temperature downwards,

_i.e._ the "gradient" of temperature, to be one degree centigrade

in 35 metres) the downward extension of such rocks might, _prima

facie_, be as much as 19 kilometres.

About this calculation we have to observe that we assume the

average radioactivity of the materials with which we have dealt

at the surface to extend uniformly all the way down, _i.e._ that

our experiments reveal the average radioactivity of a radioactive

crust. There is much to be said for this assumption. The rocks

which enter into the measurements come from all depths of the

crust. It is highly probable that the less silicious, _i.e._ the

more basic, rocks, mainly come from considerable depths; the more

acid or silica-rich rocks, from higher levels in the crust. The

radioactivity determined as the mean of the values for these two

classes of rock closely agrees with that found for intermediate

rocks, or rocks containing an intermediate amount of silica.

Clarke contends that this last class of material probably

represents the average composition of the Earth's crust so far as

it has been explored by us.

[1] The calorie referred to is the quantity of heat required to

heat one gram of water, _i.e._ one cubic centimetre of

water—through one degree centigrade.

126

It is therefore highly probable that the value found for the mean

radioactivity of acid and basic rocks, or that found for

intermediate rocks, truly represents the radioactive state of the

crust to a considerable depth. But it is easy to show that we

cannot with confidence speak of the thickness of this crust as

determinable by equating the heat outflow at the surface with the

heat production of this average rock.

This appears in the failure of a radioactive layer, taken at a

thickness of about 19-kilometres, to account for the deep-seated

high temperatures which we find to be indicated by volcanic

phenomena at many places on the surface. It is not hard to show

that the 19-kilometre layer would account for a temperature no

higher than about 270° >C. at its base.

It is true that this will be augmented beneath the sedimentary

deposits as we shall presently see; and that it is just in

association with these deposits that deep-seated temperatures are

most in evidence at the surface; but still the result that the

maximum temperature beneath the crust in general attains a value

no higher than 270° C. is hardly tenable. We conclude, then, that

some other source of heat exists beneath. This may be radioactive

in origin and may be easily accounted for if the radioactive

materials are more sparsely distributed at the base of the upper

crust. Or, again, the heat may be primeval or original heat,

still escaping from a cooling world. For our present purpose it

does not much matter which view

127

we adopt. But we must recognise that the calculated depth of 19

kilometres of crust, possessing the average radioactivity of the

surface, is excessive; for, in fact, we are compelled by the

facts to recognise that some other source of heat exists

beneath.

If the observed surface gradient of temperature persisted

uniformly downwards, at some 35 kilometres beneath the surface

there would exist temperatures (of about 1000° C.) adequate to

soften basic rocks. It is probable, however, that the gradient

diminishes downwards, and that the level at which such

temperatures exist lies rather deeper than this. It is,

doubtless, somewhat variable according to local conditions; nor

can we at all approximate closely to an estimate of the depth at

which the fusion temperatures will be reached, for, in fact, the

existence of the radioactive layer very much complicates our

estimates. In what follows we assume the depth of softening to

lie at about 40 kilometres beneath the surface of the normal

crust; that is 25 miles down. It is to be observed that Prestwich

and other eminent geologists, from a study of the facts of

crust-folding, etc., have arrived at similar estimates.[1] As a

further assumption we are probably not far wrong if we assign to

the radioactive part of this crust a thickness of about 10 or 12

kilometres; _i.e._ six or seven miles. This is necessarily a

rough approximation only; but the conclusions at which

[1] Prestwich, _Proc. Royal Soc._, xii., p. 158 _et seq._

128

we shall arrive are reached in their essential features allowing

a wide latitude in our choice of data. We shall speak of this

part of the crust as the normal radioactive layer.

An important fact is evolved from the mathematical investigation

of the temperature conditions arising from the presence of such a

radioactive layer. It is found that the greatest temperature, due

to the radioactive heat everywhere evolved in the layer—_i.e._

the temperature at its base—is proportional to the square of the

thickness of the layer. This fact has a direct bearing on the

influence of radioactivity upon mountain elevation; as we shall

now find.

The normal radioactive layer of the Earth is composed of rocks

extending—as we assume—approximately to a depth of 12 kilometres

(7.5 miles). The temperature at the base of this layer due to the

heat being continually evolved in it, is, say, t_1°. Now, let us

suppose, in the trough of the geosyncline, and upon the top of

the normal layer, a deposit of, say, 10 kilometres (6.2 miles) of

sediments is formed during a long period of continental

denudation. What is the effect of this on the temperature at the

base of the normal layer depressed beneath this load? The total

thickness of radioactive rocks is now 22 kilometres. Accordingly

we find the new temperature t_2°, by the proportion t_1° : t_2° ::

12° : 22° That is, as 144 to 484. In fact, the temperature is more

than trebled. It is true we here assume the radioactivity of the

sediments

129

and of the normal crust to be the same. The sediments are,

however, less radioactive in the proportion of 4 to 3.

Nevertheless the effects of the increased thickness will be

considerable.

Now this remarkable increase in the temperature arises entirely

from the condition attending the radioactive heating; and

involves something _additional_ to the temperature conditions

determined by the mere depression and thickening of the crust as

in the Babbage-Herschel theory. The latter theory only involves a

_shifting_ of the temperature levels (or geotherms) into the

deposited materials. The radioactive theory involves an actual

rise in the temperature at any distance from the surface; so that

_the level in the crust at which the rocks are softened is nearer

to the surface in the geosynclines than it is elsewhere in the

normal crust_ (Pl. XV, p. 118).

In this manner the rigid part of the crust is reduced in

thickness where the great sedimentary deposits have collected. A

ten-kilometre layer of sediment might result in reducing the

effective thickness of the crust by 30 per cent.; a

fourteen-kilometre layer might reduce it by nearly 50 per cent.

Even a four-kilometre deposit might reduce the effective

resistance of the crust to compressive forces, by 10 per cent.

Such results are, of course, approximate only. They show that as

the sediments grow in depth there is a rising of the geotherm of

plasticity—whatever its true temperature may be—gradually

reducing the thickness of that part

130

of the upper crust which is bearing the simultaneously increasing

compressive stresses. Below this geotherm long-continued stress

resolves itself into hydrostatic pressure; above it (there is, of

course, no sharp line of demarcation) the crust accumulates

elastic energy. The final yielding and flexure occur when the

resistant cross-section has been sufficiently diminished. It is

probable that there is also some outward hydrostaitic thrust over

the area of rising temperature, which assists in determining the

upward throw of the folds.

When yielding has begun in any geosyncline, and the materials are

faulted and overthrust, there results a considerably increased

thickness. As an instance, consider the piling up of sediments

over the existing materials of the Alps, which resulted from the

compressive force acting from south to north in the progress of

Alpine upheaval. Schmidt of Basel has estimated that from 15 to

20 kilometres of rock covered the materials of the Simplon as now

exposed, at the time when the orogenic forces were actively at

work folding and shearing the beds, and injecting into their

folds the plastic gneisses coming from beneath.[1] The lateral

compression of the area of deposition of the Laramide, already

referred to, resulted in a great thickening of the deposits. Many

other cases might be cited; the effect is always in some degree

necessarily produced.

[1] Schmidt, Ec. Geol. _Helvelix_, vol. ix., No. 4, p. 590

131

If time be given for the heat to accumulate in the lower depths

of the crushed-up sediments, here is an additional source of

increased temperature. The piled-up masses of the Simplon might

have occasioned a rise due to radioactive heating of one or two

hundred degrees, or even more; and if this be added to the

interior heat, a total of from 800° to 1000° might have prevailed

in the rocks now exposed at the surface of the mountain. Even a

lesser temperature, accompanied by the intense pressure

conditions, might well occasion the appearances of thermal

metamorphism described by Weinschenk, and for which, otherwise,

there is difficulty in accounting.[1]

This increase upon the primarily developed temperature conditions

takes place concurrently with the progress of compression; and

while it cannot be taken into account in estimating the

conditions of initial yielding of the crust, it adds an element

of instability, inasmuch as any progressive thickening by lateral

compression results in an accelerated rise of the goetherms. It

is probable that time sufficient for these effects to develop, if

not to their final, yet to a considerable extent, is often

available. The viscous movements of siliceous materials, and the

out-pouring of igneous rocks which often attend mountain

elevation, would find an explanation in such temperatures.

[1] Weinschenk, _Congrès Géol. Internat._, 1900, i., p. 332.

132

There is no more striking feature of the part here played by

radioactivity than the fact that the rhythmic occurrence of

depression and upheaval succeeding each other after great

intervals of time, and often shifting their position but little

from the first scene of sedimentation, becomes accounted for. The

source of thermal energy, as we have already remarked, is in fact

transported with the sediments—that energy which determines the

place of yielding and upheaval, and ordains that the mountain

ranges shall stand around the continental borders. Sedimentation

from this point of view is a convection of energy.

When the consolidated sediments are by these and by succeeding

movements forced upwards into mountains, they are exposed to

denudative effects greatly exceeding those which affect the

plains. Witness the removal during late Tertiary times of the

vast thickness of rock enveloping the Alps. Such great masses are

hurried away by ice, rivers, and rain. The ocean receives them;

and with infinite patience the world awaits the slow accumulation

of the radioactive energy beginning afresh upon its work. The

time for such events appears to us immense, for millions of years

are required for the sediments to grow in thickness, and the

geotherms to move upwards; but vast as it is, it is but a moment

in the life of the parent radioactive substances, whose atoms,

hardly diminished in numbers, pursue their changes while the

mountains come and go, and the

133

rudiments of life develop into its highest consummations.

To those unacquainted with the results of geological

investigation the history of the mountains as deciphered in the

rocks seems almost incredible.

The recently published sections of the Himalaya, due to H. H.

Hayden and the many distinguished men who have contributed to the

Geological Survey of India, show these great ranges to be

essentially formed of folded sediments penetrated by vast masses

of granite and other eruptives. Their geological history may be

summarised as follows

The Himalayan area in pre-Cambrian times was, in its southwestern

extension, part of the floor of a sea which covered much of what

is now the Indian Peninsula. In the northern shallows of this sea

were laid down beds of conglomerate, shale, sandstone and

limestone, derived from the denudation of Archæan rocks, which,

probably, rose as hills or mountains in parts of Peninsular India

and along the Tibetan edge of the Himalayan region. These beds

constitute the record of the long Purana Era[1] and are probably

coeval with the Algonkian of North America. Even in these early

times volcanic disturbances affected this area and the lower beds

of the Purana deposits were penetrated by volcanic outflows,

covered by sheets of lava, uplifted, denuded and again submerged

[1] See footnote, p. 139.

134

beneath the waters. Two such periods of instability have left

their records in the sediments of the Purana sea.

The succeeding era—the Dravidian Era—opens with Haimanta

(Cambrian) times. A shallow sea now extended over Kumaun, Garwal,

and Spiti, as well as Kashmir and ultimately over the Salt Range

region of the Punjab as is shown by deposits in these areas. This

sea was not, however, connected with the Cambrian sea of Europe.

The fossil faunas left by the two seas are distinct.

After an interval of disturbance during closing Haimanta times,

geographical changes attendant on further land movements

occurred. The central sea of Asia, the Tethys, extended westwards

and now joined with the European Paleozoic sea; and deposits of

Ordovician and Silurian age were laid down:—the Muth deposits.

The succeeding Devonian Period saw the whole Northern Himalayan

area under the waters of the Tethys which, eastward, extended to

Burma and China and, westward, covered Kashmir, the Hindu Kush

and part of Afghanistan. Deposits continued to be formed in this

area till middle Carboniferous times.

Near. the close of the Dravidian Era Kashmir became convulsed by

volcanic disturbance and the Penjal traps were ejected. It was a

time of worldwide disturbance and of redistribution of land and

water. Carboniferous times had begun, and the geographical

changes in

135

the southern limits of the Tethys are regarded as ushering in a

new and last era in Indian geological history the Aryan Bra.

India was now part of Gondwanaland; that vanished continent which

then reached westward to South Africa and eastward to Australia.

A boulder-bed of glacial origin, the Talchir Boulder-bed, occurs

in many surviving parts of this great land. It enters largely

into the Salt Range deposits. There is evidence that extensive

sheets of ice, wearing down the rocks of Rajputana, shoved their

moraines northward into the Salt Range Sea; then, probably, a

southern extension of the Tethys.

Subsequent to this ice age the Indian coalfields of the Gondwana

were laid down, with beds rich in the Glossopteris and

Gangamopteris flora. This remarkable carboniferous flora extends

to Southern Kashmir, so that it is to be inferred that this

region was also part of the main Gondwanaland. But its emergence

was but for a brief period. Upper Carboniferous marine deposits

succeeded; and, in fact, there was no important discontinuity in

the deposits in this area from Panjal times till the early

Tertiaries. During the whole of which vast period Kashmir was

covered with the waters of the Tethys.

The closing Dravidian disturbances of the Kashmir region did not,

apparently, extend to the eastern Himalayan area. But the

Carboniferous Period was, in this

136

eastern area, one of instability, culminating, at the close of

the Period, in a steady rise of the land and a northward retreat

of the Tethys. Nearly the entire Himalaya east of Kashmir became

a land surface and remained exposed to denudative forces for so

long a time that in places the whole of the Carboniferous,

Devonian, and a large part of the Silurian and Ordovician

deposits were removed—some thousands of feet in thickness—before

resubmergence in the Tethys occurred.

Towards the end of the Palaeozoic Age the Aryan Tethys receded

westwards, but still covered the Himalaya and was still connected

with the European Palæozoic sea. The Himalayan area (as well as

Kashmir) remained submerged in its waters throughout the entire

Mesozoic Age.

During Cretaceous times the Tethys became greatly extended,

indicating a considerable subsidence of northwestern India,

Afghanistan, Western Asia, and, probably, much of Tibet. The

shallow-water character of the deposits of the Tibetan Himalaya

indicates, however, a coast line near this region. Volcanic

materials, now poured out, foreshadow the incoming of the great

mountain-building epoch of the Tertiary Era. The enormous mass of

the Deccan traps, possessing a volume which has been estimated at

as much as 6,000 cubic miles, was probably extruded over the

Northern Peninsular region during late Cretaceous times. The sea

now began to retreat, and by the close of

137

the Eocene, it had moved westward to Sind and Baluchistan. The

movements of the Earth's crust were attended by intense volcanic

activity, and great volumes of granite were injected into the

sediments, followed by dykes and outflows of basic lavas.

The Tethys vanished to return no more. It survives in the

Mediterranean of today. The mountain-building movements continued

into Pliocene times. The Nummulite beds of the Eocene were, as

the result, ultimately uplifted 18,500 feet over sea level, a

total uplift of not less than 20,000 feet.

Thus with many vicissitudes, involving intervals of volcanic

activity, local uplifting, and extensive local denudation, the

Himalaya, which had originated in the sediments of the ancient

Purana sea, far back in pre-Cambrian times, and which had

developed potentially in a long sequence of deposits collecting

almost continuously throughout the whole of geological time,

finally took their place high in the heavens, where only the

winds—faint at such altitudes—and the lights of heaven can visit

their eternal snows.[1]

In this great history it is significant that the longest

continuous series of sedimentary deposits which the world has

known has become transfigured into the loftiest elevation upon

its surface.

[1] See A Sketch of the _Geography and Geology of the Himalaya

Mountains and Tibet_. By Colonel S. G. Burrard, R.E., F.R.S., and

H. H. Hayden, F.G.S., Part IV. Calcutta, 1908.

138

The diagrammatic sections of the Himalaya accompanying this brief

description arc taken from the monograph of Burrard and Hayden

(loc. cit.) on the Himalaya. Looking at the sections we see that

some of the loftiest summits are sculptured in granite and other

crystalline rocks. The appearance of these materials at the

surface indicates the removal by denudation and the extreme

metamorphism of much sedimentary deposit. The crystalline rocks,

indeed, penetrate some of the oldest rocks in the world. They

appear in contact with Archaean, Algonkian or early Palaeozoic

rocks. A study of the sections reveals not only the severe earth

movements, but also the immense amount of sedimentary deposits

involved in the genesis of these alps. It will be noted that the

vertical scale is not exaggerated relatively to the

horizontal.[1] Although there is no evidence of mountain

building

[1] To those unacquainted with the terminology of Indian geology

the following list of approximate equivalents in time will be of

use

Ngari Khorsum Beds - Pleistocene.

Siwalik Series -     Miocene and Pliocene.

Sirmur Series -      Oligocene.

Kampa System -       Eocene and Cretaceous.

Lilang System -      Triassic.

Kuling System -      Permian.

Gondwana System -    Carboniferous.

Kenawar System -     Carboniferous and Devonian

Muth System -        Silurian.

Haimanta System -    Mid. and Lower Cambrian.

Purana Group -       Algonkian.

Vaikrita System -    Archæan.

Daling Series -      Archæan.

139

on a large scale in the Himalayan area till the Tertiary

upheaval, it is, in the majority of cases, literally correct to

speak of the mountains as having their generations like organic

beings, and passing through all the stages of birth, life, death

and reproduction. The Alps, the Jura, the Pyrenees, the Andes,

have been remade more than once in the course of geological time,

the _débris_ of a worn-out range being again uplifted in succeeding

ages.

Thus to dwell for a moment on one case only: that of the

Pyrenees. The Pyrenees arose as a range of older Palmozoic rocks

in Devonian times. These early mountains, however, were

sufficiently worn out and depressed by Carboniferous times to

receive the deposits of that age laid down on the up-turned edges

of the older rocks. And to Carboniferous succeeded Permian,

Triassic, Jurassic and Lower Cretaceous sediments all laid down

in conformable sequence. There was then fresh disturbance and

upheaval followed by denudation, and these mountains, in turn,

became worn out and depressed beneath the ocean so that Upper

Greensand rocks were laid down unconforrnably on all beneath. To

these now succeeded Upper Chalk, sediments of Danian age, and so

on, till Eocene times, when the tale was completed and the

existing ranges rose from the sea. Today we find the folded

Nummulitic strata of Eocene age uplifted 11,000 feet, or within

200 feet of the greatest heights of the Pyrenees. And so they

stand awaiting

140

the time when once again they shall "fall into the portion of

outworn faces."[1]

Only mountains can beget mountains. Great accumulations of

sediment are a necessary condition for the localisation of

crust-flexure. The earliest mountains arose as purely igneous or

volcanic elevations, but the generations of the hills soon

originated in the collection of the _débris_, under the law of

gravity, in the hollow places. And if a foundered range is

exposed now to our view encumbered with thousands of feet of

overlying sediments we know that while the one range was sinking,

another, from which the sediments were derived, surely existed.

Through the "windows" in the deep-cut rocks of the Swiss valleys

we see the older Carboniferous Alps looking out, revisiting the

sun light, after scores of millions of years of imprisonment. We

know that just as surely as the Alps of today are founding by

their muddy torrents ranges yet to arise, so other primeval Alps

fed into the ocean the materials of these buried pre-Permian

rocks.

This succession of events only can cease when the rocks have been

sufficiently impoverished of the heat-producing substances, or

the forces of compression shall have died out in the surface

crust of the earth.

It seems impossible to escape the conclusion that in the great

development of ocean-encircling areas of

[1] See Prestwich, _Chemical and Physical Geology_, p. 302.

141

deposition and crustal folding, the heat of radioactivity has

been a determining factor. We recognise in the movements of the

sediments not only an influence localising and accelerating

crustal movements, but one which, in subservience to the primal

distribution of land and water, has determined some of the

greatest geographical features of the globe.

It is no more than a step to show that bound up with the

radioactive energy are most of the earthquake and volcanic

phenomena of the earth. The association of earthquakes with the

great geosynclines is well known. The work of De Montessus showed

that over 94 per cent. of all recorded shocks lie in the

geosynclinal belts. There can be no doubt that these

manifestations of instability are the results of the local

weakness and flexure which originated in the accumulation of

energy denuded from the continents. Similarly we may view in

volcanoes phenomena referable to the same fundamental cause. The

volcano was, in fact, long regarded as more intimately connected

with earthquakes than it, probably, actually is; the association

being regarded in a causative light, whereas the connexion is

more that of possessing a common origin. The girdle of volcanoes

around the Pacific and the earthquake belt coincide. Again, the

ancient and modern volcanoes and earthquakes of Europe are

associated with the geosyncline of the greater Mediterranean, the

Tethys of Mesozoic times. There is no difficulty in understanding

in a

142

general way the nature of the association. The earthquake is the

manifestation of rupture and slip, and, as Suess has shown, the

epicentres shift along that fault line where the crust has

yielded.[1] The volcano marks the spot where the zone of fusion

is brought so high in the fractured crust that the melted

materials are poured out upon the surface.

In a recent work on the subject of earthquakes Professor Hobbs

writes: "One of the most interesting of the generalisations which

De Montessus has reached as a result of his protracted studies,

is that the earthquake districts on the land correspond almost

exactly to those belts upon the globe which were the almost

continuous ocean basins of the long Secondary era of geological

history. Within these belts the sedimentary formations of the

crust were laid down in the greatest thickness, and the

formations follow each other in relatively complete succession.

For almost or quite the whole of this long era it is therefore

clear that the ocean covered these zones. About them the

formations are found interrupted, and the lacuna indicate that

the sea invaded the area only to recede from it, and again at

some later period to transgress upon it. For a long time,

therefore, these earthquake belts were the sea basins—the

geosynclines. They became later the rising mountains of the

Tertiary period, and mountains they

[1] Suess, _The Face of the Earth_, vol. ii., chap. ii.

143

are today. The earthquake belts are hence those portions of the

earth's crust which in recent times have suffered the greatest

movements in a vertical direction—they are the most mobile

portions of the earth's crust."[1] Whether the movements

attending mountain elevation and denudation are a connected and

integral part of those wide geographical changes which result in

submergence and elevation of large continental areas, is an

obscure and complex question. We seem, indeed, according to the

views of some authorities, hardly in a position to affirm with

certainty that such widespread movements of the land have

actually occurred, and that the phenomena are not the outcome of

fluctuations of oceanic level; that our observations go no

further than the recognition of positive and negative movements

of the strand. However this may be, the greater part of

mechanical denudation during geological time has been done on the

mountain ranges. It is, in short, indisputable that the orogenic

movements which uplift the hills have been at the basis of

geological history. To them the great accumulations of sediments

which now form so large a part of continental land are mainly

due. There can be no doubt of the fact that these movements have

swayed the entire history, both inorganic and organic, of the

world in which we live.

[1] Hobbs, _Earthquakes_, p. 58.

144

To sum the contents of this essay in the most general terms, we

find that in the conception of denudation as producing the

convection and accumulation of radiothermal energy the surface

features of the globe receive a new significance. The heat of the

earth is not internal only, but rather a heat-source exists at

the surface, which, as we have seen, cannot prevail to the same

degree within; and when the conditions become favourable for the

aggregation of the energy, the crust, heated both from beneath

and from above, assumes properties more akin to those of its

earlier stages of development, the secular heat-loss being

restored in the radioactive supplies. These causes of local

mobility have been in operation, shifting somewhat from place to

place, and defined geographically by the continental masses

undergoing denudation, since the earliest times.

145

ALPINE STRUCTURE

AN intelligent observer of the geological changes progressing in

southern Europe in Eocene times would have seen little to inspire

him with a premonition of the events then developing. The

Nummulitic limestones were being laid down in that enlarged

Mediterranean which at this period, save for a few islands,

covered most of south Europe. Of these stratified remains, as

well as of the great beds of Cretaceous, Jurassic, Triassic, and

Permian sediments beneath, our hypothetical observer would

probably have been regardless; just as today we observe, with an

indifference born of our transitoriness, the deposits rapidly

gathering wherever river discharge is distributing the sediments

over the sea-floor, or the lime-secreting organisms are actively

at work. And yet it took but a few millions of years to uplift

the deposits of the ancient Tethys; pile high its sediments in

fold upon fold in the Alps, the Carpathians, and the Himalayas;

and—exposing them to the rigours of denudation at altitudes where

glaciation, landslip, and torrent prevail—inaugurate a new epoch

of sedimentation and upheaval.

146

In the case of the Alps, to which we wish now specially to refer,

the chief upheaval appears to have been in Oligocene times,

although movement continued to the close of the Pliocene. There

was thus a period of some millions of years within which the

entire phenomena were comprised. Availing ourselves of Sollas'

computations,[1] we may sum the maximum depths of sedimentary

deposits of the geological periods concerned as follows:—

Pliocene - - - - - 3,950 m.

Miocene  - - - - - 4,250 m.

Oligocene  - - - - 3,660 m.

Eocene - - - - - - 6,100 m.

and assuming that the orogenic forces began their work in the

last quarter of the Eocene period, we have a total of 13,400 m.

as some measure of the time which elapsed. At the rate of io

centimetres in a century these deposits could not have collected

in less than 13.4 millions of years. It would appear that not

less than some ten millions of years were consumed in the genesis

of the Alps before constructive movements finally ceased.

The progress of the earth-movements was attended by the usual

volcanic phenomena. The Oligocene and Miocene volcanoes extended

in a band marked by the Auvergne, the Eiffel, the Bohemian, and

the eastern Carpathian eruptions; and, later, towards the close

of the movements in Pliocene times, the south border

[1] Sollas, Anniversary Address, Geol. Soc., London, 1909.

147

regions of the Alps became the scene of eruptions such as those

of Etna, Santorin, Somma (Vesuvius), etc.

We have referred to these well-known episodes with two objects in

view: to recall to mind the time-interval involved, and the

evidence of intense crustal disturbance, both dynamic and

thermal. According to views explained in a previous essay, the

energetic effects of radium in the sediments and upper crust were

a principal factor in localising and bringing about these

results. We propose now to inquire if, also, in the more intimate

structure of the Alps, the radioactive energy may not have borne

a part.

What we see today in the Alps is but a residue spared by

denudation. It is certain that vast thicknesses of material have

disappeared. Even while constructive effects were still in

progress, denudative forces were not idle. Of this fact the

shingle accumulations of the Molasse, where, on the northern

borders of the Alps, they stand piled into mountains, bear

eloquent testimony. In the sub-Apennine series of Italy, the

great beds of clays, marls, and limestones afford evidence of

these destructive processes continued into Pliocene times. We

have already referred to Schmidt's estimate that the sedimentary

covering must have in places amounted to from 15,000 to 20,000

metres. The evidence for this is mainly tectonic or structural;

but is partly forthcoming in the changes which the materials now

open to our inspection plainly reveal. Thus it is impos-

148

sible to suppose that gneissic rocks can become so far plastic as

to flow in and around the calcareous sediments, or be penetrated

by the latter—as we see in the Jungfrau and elsewhere—unless

great pressures and high temperatures prevailed. And, according

to some writers, the temperatures revealed by the intimate

structural changes of rock-forming minerals must have amounted to

those of fusion. The existence of such conditions is supported by

the observation that where the.crystallisation is now the most

perfect, the phenomena of folding and injection are best

developed.[1] These high temperatures would appear to be

unaccountable without the intervention of radiothermal effects;

and, indeed, have been regarded as enigmatic by observers of the

phenomena in question. A covering of 20,000 metres in thickness

would not occasion an earth-temperature exceeding 500° C. if the

gradients were such as obtain in mountain regions generally; and

600° is about the limit we could ascribe to the purely passive

effects of such a layer in elevating the geotherms.

Those who are still unacquainted with the recently published

observations on the structure of the Alps may find it difficult

to enter into what has now to be stated; for the facts are,

indeed, very different from the generally preconceived ideas of

mountain formation. Nor can we wonder that many geologists for

long held

[1] Weinschenk, C. R. _Congrès Géol._, 1900, p. 321, et seq.

149

back from admitting views which appeared so extreme. Receptivity

is the first virtue of the scientific mind; but, with every

desire to lay aside prejudice, many felt unequal to the

acceptance of structural features involving a folding of the

earth-crust in laps which lay for scores of miles from country to

country, and the carriage of mountainous materials from the south

of the Alps to the north, leaving them finally as Alpine ranges

of ancient sediments reposing on foundations of more recent date.

The historian of the subject will have to relate how some who

finally were most active in advancing the new views were at first

opposed to them. In the change of conviction of these eminent

geologists we have the strongest proof of the convincing nature

of the observations and the reality of the tectonic features upon

which the recent views are founded.

The lesser mountains which stand along the northern border of the

great limestone Alps, those known as the Préalpes, present the

strange characteristic of resting upon materials younger than

themselves. Such mountains as the remarkable-looking Mythen, near

Schwyz, for instance, are weathered from masses of Triassic and

Jurassic rock, and repose on the much more recent Flysch. In

sharp contrast to the Flysch scenery, they stand as abrupt and

gigantic erratics, which have been transported from the central

zone of the Alps lying far to the south. They are strangers

petrologically,

150

stratigraphically, and geographically,[1] to the locality in

which they now occur. The exotic materials may be dolomites,

limestones, schists, sandstones, or rocks of igneous origin. They

show in every case traces of the severe dynamic actions to which

they have been subjected in transit. The igneous, like the

sedimentary, klippen, can be traced to distant sources; to the

massif of Belladonne, to Mont Blanc, Lugano, and the Tyrol. The

Préalpes are, in fact, mountains without local roots.

In this last-named essential feature, the Préalpes do not differ

from the still greater limestone Alps which succeed them to the

south. These giants, _e.g._ the Jungfrau, Wetterhorn, Eiger, etc.,

are also without local foundations. They have been formed from

the overthrown and drawn-out anticlines of great crust-folds,

whose synclines or roots are traceable to the south side of the

Rhone Valley. The Bernese Oberland originated in the piling-up of

four great sheets or recumbent folds, one of which is continued

into the Préalpes. With Lugeon[2] we may see in the phenomenon of

the formation of the Préalpes a detail; regarding it as a normal

expression of that mechanism which has created the Swiss Alps.

For these limestone masses of the Oberland are not indications of

a merely local shift of the sedimentary covering of the Alps.

Almost the whole covering has

[1] De Lapparent, _Traité de Géologie_, p. 1,785.

[2] Lugeon, _Bulletin Soc. Géol. de France_, 1901, p. 772.

151

been pushed over and piled up to the north. Lugeon[l] concludes

that, before denudation had done its work and cut off the

Préalpes from their roots, there would have been found sheets, to

the number of eight, superimposed and extending between the Mont

Blanc massif and the massif of the Finsteraarhorn: these sheets

being the overthrown folds of the wrinkled sedimentary covering.

The general nature of the alpine structure

{Fig. 8}

will be understood from the presentation of it diagrammatically

after Schmidt of Basel (Fig. 8).[2] The section extends from

north to south, and brings out the relations of the several

recumbent folds. We must imagine almost the whole of these

superimposed folds now removed from the central regions of the

Alps by denudation,

[1] Lugeon, _loc. cit._

[2] Schmidt, _Ec. Geol. Helvetiae_, vol. ix., No. 4.

152

and leaving the underlying gneisses rising through the remains of

Permian, Triassic, and Jurassic sediments; while to the north the

great limestone mountains and further north still, the Préalpes,

carved from the remains of the recumbent folds, now stand with

almost as little resemblance to the vanished mountains as the

memories of the past have to its former intense reality.

These views as to the origin of the Alps, which are shared at the

present day by so many distinguished geologists, had their origin

in the labours of many now gone; dating back to Studer; finding

their inspiration in the work of Heim, Suess, and Marcel

Bertrand; and their consummation in that of Lugeon, Schardt,

Rothpletz, Schmidt, and many others. Nor must it be forgotten

that nearer home, somewhat similar phenomena, necessarily on a

smaller scale, were recognised by Lapworth, twenty-six years ago,

in his work on the structure of the Scottish Highlands.

An important tectonic principle underlies the development of the

phenomena we have just been reviewing. The uppermost of the

superimposed recumbent folds is more extended in its development

than those which lie beneath. Passing downwards from the highest

of the folds, they are found to be less and less extended both in

the northerly and in the southerly direction, speaking of the

special case—the Alps—now before us. This feature might be

described somewhat differently. We might say that those folds

which had their roots farther

153

to the south were the most drawn-out towards the north: or again

we might say that the synclinal or deep-seated part of the fold

has lagged behind the anticlinal or what was originally the

highest part of the fold, in the advance of the latter to the

north. The anticline has advanced relatively to the syncline. To

this law one exception only is observed in the Swiss Alps; the

sheet of the Brèche (_Byecciendecke_) falls short, in its northerly

extension, of the underlying fold, which extends to form the

Préalpes.

Contemplating such a generalised section as Professor Schmidt's,

or, indeed, more particular sections, such as those in the Mont

Blanc Massif by Marcel Bertrand,[1] of the Dent de Morcles,

Diablerets, Wildhorn, and Massif de la Brèche by Lugeon,[2] or

finally Termier's section of the Pelvoux Massif,[3] one is

reminded of the breaking of waves on a sloping beach. The wave,

retarded at its base, is carried forward above by its momentum,

and finally spreads far up on the strand; and if it could there

remain, the succeeding wave must necessarily find itself

superimposed upon the first. But no effects of inertia, no

kinetic effects, may be called to our aid in explaining the

formation of mountains. Some geologists have accordingly supposed

that in order to account for

[1] Marcel Bertrand, _Cong. Géol. Internat._, 1900, Guide Géol.,

xiii. a, p. 41.

[2] Lugeon, _loc. cit._, p. 773.

[3] De Lapparent, _Traite de Géol._, p. 1,773.

154

the recumbent folds and the peculiar phenomena of increasing

overlap, or _déferlement_, an obstacle, fixed and deep-seated, must

have arrested the roots or synclines of the folds, and held them

against translational motion, while a movement of the upper crust

drew out and carried forward the anticlines. Others have

contented themselves by recording the facts without advancing any

explanatory hypothesis beyond that embodied in the incontestable

statement that such phenomena must be referred to the effects of

tangential forces acting in the Earth's crust.

It would appear that the explanation of the phenomena of

recumbent folds and their _déferlement_ is to be obtained directly

from the temperature conditions prevailing throughout the

stressed pile of rocks; and here the subject of mountain

tectonics touches that with which we were elsewhere specially

concerned—the geological influence of accumulated radioactive

energy.

As already shown[1], a rise of temperature due to this source of

several hundred degrees might be added to such temperatures as

would arise from the mere blanketing of the Earth, and the

consequent upward movement of the geotherms. The time element is

here the most important consideration. The whole sequence of

events from the first orogenic movements to the final upheaval in

Pliocene times must probably have occupied not less than ten

million years.

[1] _Mountain Genesis_, p. 129, et seq.

155

Unfortunately the full investigation of the distribution of

temperature after any given time is beset with difficulties; the

conditions being extremely complex. If the radioactive heating

was strictly adiabatic—that is, if all the heat was conserved and

none entered from without—the time required for the attainment of

the equilibrium radioactive temperature would be just about six

million years. The conditions are not, indeed, adiabatic; but, on

the other hand, the rocks upraised by lateral pressure were by no

means at 0° C. to start with. They must be assumed to have

possessed such temperatures as the prior radiothermal effects,

and the conducted heat from the Earth's interior, may have

established.

It would from this appear probable that if a duration of ten

million years was involved, the equilibrium radioactive

temperatures must nearly have been attained. The effects of heat

conducted from the underlying earthcrust have to be added,

leading to a further rise in temperature of not less than 500° or

600° . In such considerations the observed indications of high

temperatures in materials now laid bare by denudation, probably

find their explanation (P1. XIX).

The first fact that we infer from the former existence of such a

temperature distribution is the improbability, indeed the

impossibility, that anything resembling a rigid obstacle, or

deep-seated "horst," can have existed beneath the present

surface-level, and opposed the northerly movement of the

deep-lying synclines. For

156

such a horst can only have been constituted of some siliceous

rock-material such as we find everywhere rising through the

worn-down sediments of the Alps; and the idea that this could

retain rigidity under the prevailing temperature conditions, must

be dismissed. There is no need to labour this question; the horst

cannot have existed. To what, then, is the retardation of the

lower parts of the folds, their overthrow, above, to the north,

and their _déferlement_, to be ascribed?

A little consideration shows that the very conditions of high

temperature and viscosity, which render untenable the hypothesis

of a rigid obstacle, suffice to afford a full explanation of the

retardation of the roots of the folds. For directed translatory

movements cannot be transmitted through a fluid, pressure in

which is necessarily hydrostatic, and must be exerted equally in

every direction. And this applies, not only to a fluid, but to a

body which will yield viscously to an impressed force. There will

be a gradation, according as viscosity gives place to rigidity,

between the states in which the applied force resolves itself

into a purely hydrostatic pressure, and in which it is

transmitted through the material as a directed thrust. The nature

of the force, in the most general case, of course, has to be

considered; whether it is suddenly applied and of brief duration,

or steady and long-continued. The latter conditions alone apply

to the present case.

It follows from this that, although a tangential force

157

or pressure be engendered by a crustal movement occurring to the

south, and the resultant effects be transmitted northwards, these

stresses can only mechanically affect the rigid parts of the

crust into which they are carried. That is to say, they may

result in folding and crushing, or horizontally transporting, the

upper layers of the Earth's crust; but in the deeper-lying

viscous materials they must be resolved into hydrostatic pressure

which may act to upheave the overlying covering, but must refuse

to transmit the horizontal translatory movements affecting the

rigid materials above.

Between the regions in which these two opposing conditions

prevail there will be no hard and fast line; but with the

downward increase of fluidity there will be a gradual failure of

the mechanical conditions and an increase of the hydrostatic.

Thus while the uppermost layers of the crust may be transported

to the full amount of the crustal displacement acting from the

south (speaking still of the Alps) deeper down there will be a

lesser horizontal movement, and still deeper there is no

influence to urge the viscous rock-materials in a northerly

direction. The consequences of these conditions must be the

recumbence of the folds formed under the crust-stress, and their

_déferlement_ towards the north. To see this, we must follow the

several stages of development.

The earliest movements, we may suppose, result in flexures of the

Jura-Mountain type—that is, in a

158

succession of undulations more or less symmetrical. As the

orogenic force continues and develops, these undulations give

place to folds, the limbs of which are approximately vertical,

and the synclinal parts of which become ever more and more

depressed into the deeper, and necessarily hotter, underlying

materials; the anticlines being probably correspondingly

elevated. These events are slowly developed, and the temperature

beneath is steadily rising in consequence of the conducted

interior heat, and the steady accumulation of radioactive energy

in the sedimentary rocks and in the buried radioactive layer of

the Earth. The work expended on the crushed and sheared rock also

contributes to the developing temperature. Thus the geotherms

must move upwards, and the viscous conditions extend from below;

continually diminishing the downward range of the translatory

movements progressing in the higher parts. While above the folded

sediments are being carried northward, beneath they are becoming

anchored in the growing viscosity of the medium. The anticlines

will bend over, and the most southerly of the folds will

gradually become pushed or bent over those lying to the north.

Finally, the whole upper part of the sheaf will become

horizontally recumbent; and as the uppermost folds will be those

experiencing the greatest effects of the continued displacement,

the _déferlement_ or overlap must necessarily arise.

We may follow these stages of mountain evolution

159

in a diagram (Fig. 9) in which we eliminate intermediate

conditions, and regard the early and final stages of development

only. In the upper sketch we suppose the lateral compression much

developed and the upward movement of the geotherms in progress.

The dotted line may be assumed to be a geotherm having a

temperature of viscosity. If the conditions here shown persist

{Fig. 9}

indefinitely, there is no doubt that the only further

developments possible are the continued crushing of the sediments

and the bodily displacement of the whole mass to the north. The

second figure is intended to show in what manner these results

are evaded. The geotherm of viscosity has risen. All above it is

affected mechanically by the continuing stress, and borne

northwards in varying

160

degree depending upon the rigidity. The folds have been

overthrown and drawn out; those which lay originally most to the

south have become the uppermost; and, experiencing the maximum

amount of displacement, overlap those lying beneath. There has

also been a certain amount of upthrow owing to the hydrostatic

pressure. This last-mentioned element of the phenomena is of

highly indeterminate character, for we know not the limits to

which the hydrostatic pressure may be transmitted, and where it

may most readily find relief. While, according to some of the

published sections, the uplifting force would seem to have

influenced the final results of the orogenic movements, a

discussion of its effects would not be profitable.

161

OTHER MINDS THAN OURS?

IN the year 1610 Galileo, looking through his telescope then

newly perfected by his own hands, discovered that the planet

Jupiter was attended by a train of tiny stars which went round

and round him just as the moon goes round the Earth.

It was a revelation too great to be credited by mankind. It was

opposed to the doctrine of the centrality of the Earth, for it

suggested that other worlds constituted like ours might exist in

the heavens.

Some said it was a mere optic illusion; others that he who looked

through such a tube did it at the peril of his soul—it was but a

delusion of Satan. Galileo converted a few of the unbelievers who

had the courage to look through his telescope. To the others he

said, he hoped they would see those moons on their way to heaven.

Old as this story is it has never lost its pathos or its

teaching.

The spirit which assailed Galileo's discoveries and which finally

was potent to overshadow his declining years, closed in former

days the mouths of those who asked the question written at the

head of this lecture: "Are we to believe that there are other

minds than ours?"

162

Today we consider the question in a very different spirit. Few

would regard it as either foolish or improper. Its intense

interest would be admitted by all, and but for the limitations

closing our way on every side it would, doubtless, attract the

most earnest investigation. Even on the mere balance of judgment

between the probable and the improbable, we have little to go on.

We know nothing definitely as to the conditions under which life

may originate: whether these are such as to be rare almost to

impossibility, or common almost to certainty. Only within narrow

limits of temperature and in presence of certain of the elements,

can life like ours exist, and outside these conditions life, if

such there be, must be different from ours. Once originated it is

so constituted as to assail the energies around it and to advance

from less to greater. Do we know more than these vague facts?

Yes, we have in our experience one other fact and one involving

much.

We know that our world is very old; that life has been for many

millions of years upon it; and that Man as a thinking being is

but of yesterday. Here is then a condition to be fulfilled. To

every world is physically assigned a limit to the period during

which it is habitable according to our knowledge of life and its

necessities. This limit passed and rationality missed, the chance

for that world is gone for ever, and other minds than ours

assuredly will not from it contemplate the universe. Looking at

our own world we see that the tree of life has,

163

indeed, branched, leaved and, possibly, budded many times; it

never bloomed but once.

All difficulties dissolve and speculations become needless under

one condition only: that in which rationality may be inferred

directly or indirectly by our observations on some sister world

in space, This is just the evidence which in recent years has

been claimed as derived from a study of the surface of Mars. To

that planet our hope of such evidence is restricted. Our survey

in all other directions is barred by insurmountable difficulties.

Unless some meteoric record reached our Earth, revelationary of

intelligence on a perished world, our only hope of obtaining such

evidence rests on the observation of Mars' surface features. To

this subject we confine our attention in what follows.

The observations made during recent years upon the surface

features of Mars have, excusably enough, given rise to

sensational reports. We must consider under what circumstances

these observations have been made.

Mars comes into particularly favourable conditions for

observation every fifteen years. It is true that every two years

and two months we overtake him in his orbit and he is then in

"opposition." That is, the Earth is between him and the sun: he

is therefore in the opposite part of the heavens to the sun. Now

Mars' orbit is very excentric, sometimes he is 139 million miles

from the sun, and sometimes he as as much as 154 million miles

from the sun. The Earth's orbit is, by comparison, almost

164

a circle. Evidently if we pass him when he is nearest to the sun

we see him at his best; not only because he is then nearest to

us, but because he is then also most brightly lit. In such

favourable oppositions we are within 35 million miles of him; if

Mars was in aphelion we would pass him at a distance of 61

million miles. Opposition occurs under the most favourable

circumstances every fifteen years. There was one in 1862, another

in 1877, one in 1892, and so on.

When Mars is 35 million miles off and we apply a telescope

magnifying 1,000 diameters, we see him as if placed 35,000 miles

off. This would be seven times nearer than we see the moon with

the naked eye. As Mars has a diameter about twice as great as

that of the moon, at such a distance he would look fourteen times

the diameter of the moon. Granting favourable conditions of

atmosphere much should be seen.

But these are just the conditions of atmosphere of which most of

the European observatories cannot boast. It is to the honour of

Schiaparelli, of Milan, that under comparatively unfavourable

conditions and with a small instrument, he so far outstripped his

contemporaries in the observation of the features of Mars that

those contemporaries received much of his early discoveries with

scepticism. Light and dark outlines and patches on the planet's

surface had indeed been mapped by others, and even a couple of

the canals sighted; but at the opposition of 1877 Schiaparelli

first mapped any considerable

165

number of the celebrated "canals" and showed that these

constituted an extraordinary and characteristic feature of the

planet's geography. He called them "canali," meaning thereby

"channels." It is remarkable indeed that a mistranslation appears

really responsible for the initiation of the idea that these

features are canals.

In 1882 Schiaparelli startled the astronomical world by declaring

that he saw some of the canals double—that is appearing as two

parallel lines. As these lines span the planet's surface for

distances of many thousands of miles the announcement naturally

gave rise to much surprise and, as I have said, to much

scepticism. But he resolutely stuck to his statement. Here is his

map of 1882. It is sufficiently startling.

In 1892 he drew a new map. It adds a little to the former map,

but the doubling was not so well seen. It is just the strangest

feature about this doubling that at times it is conspicuous, at

times invisible. A line which is distinctly seen as a single line

at one time, a few weeks later will appear distinctly to consist

of two parallel lines; like railway tracks, but tracks perhaps

200 miles apart and up to 3,000 or even 4,000 miles in length.

Many speculations were, of course, made to account for the origin

of such features. No known surface peculiarity on the Earth or

moon at all resembles these features. The moon's surface as you

know is cracked and

166

streaked. But the cracks are what we generally find cracks to

be—either aimless, wandering lines, or, if radiating from a

centre, then lines which contract in width as they leave the

point of rupture. Where will we find cracks accurately parallel

to one another sweeping round a planet's face with steady

curvature for, 4,000 miles, and crossing each other as if quite

unhampered by one another's presence? If the phenomenon on Mars

be due to cracks they imply a uniformity in thickness and

strength of crust, a homogeneity, quite beyond all anticipation.

We will afterwards see that the course of the lines is itself

further opposed to the theory that haphazard cracking of the

crust of the planet is responsible for the lines. It was also

suggested that the surface of the planet was covered with ice and

that these were cracks in the ice. This theory has even greater

difficulties than the last to contend with. Rivers have been

suggested. A glance at our own maps at once disposes of this

hypothesis. Rivers wander just as cracks do and parallel rivers

like parallel cracks are unknown.

In time the many suggestions were put aside. One only remained.

That the lines are actually the work of intelligence; actually

are canals, artificially made, constructed for irrigation

purposes on a scale of which we can hardly form any conception

based on our own earthly engineering structures.

During the opposition of 1894, Percival Lowell, along with A. E.

Douglass, and W. H. Pickering,

167

observed the planet from the summit of a mountain in Arizona,

using an 18-inch refracting telescope and every resource of

delicate measurement and spectroscopy. So superb a climate

favoured them that for ten months the planet was kept under

continual observation. Over 900 drawings were made and not only

were Schiaparelli's channels confirmed, but they added 116 to his

79, on that portion of the planet visible at that opposition.

They made the further important discovery that the lines do not

stop short at the dark regions of the planet's surface, as

hitherto believed, but go right on in many cases; the curvature

of the lines being unaltered.

Lowell is an uncompromising advocate of the "canal" theory. If

his arguments are correct we have at once an answer to our

question, "Are there other minds than ours?"

We must consider a moment Lowell's arguments; not that it is my

intention to combat them. You must form your own conclusions. I

shall lay before you another and, as I venture to think, more

adequate hypothesis in explanation of the channels of

Schiaparelli. We learn, however, much from Lowell's book—it is

full of interest.[1]

Lowell lays a deep foundation. He begins by showing that Mars has

an atmosphere. This must be granted him till some counter

observations are made.

[1] _Mars_, by Percival Lowell (Longmans, Green & Co.), 1896,

168

It is generally accepted. What that atmosphere is, is another

matter. He certainly has made out a good case for the presence of

water as one of its constituents,

It was long known that Mars possessed white regions at his poles,

just as our Earth does. The waning of these polar snows—if indeed

they are such—with the advance of the Martian summer, had often

been observed. Lowell plots day by day this waning. It is evident

from his observations that the snowfall must be light indeed. We

see in his map the south pole turned towards us. Mars in

perihelion always turns his south pole towards the sun and

therefore towards the Earth. We see that between the dates June

3rd to August 3rd—or in two months—the polar snow had almost

completely vanished. This denotes a very scanty covering. It must

be remembered that Mars even when nearest to the sun receives but

half our supply of solar heat and light.

But other evidence exists to show that Mars probably possesses

but little water upon his surface. The dark places are not

water-covered, although they have been named as if they were,

indeed, seas and lakes. Various phenomena show this. The canals

show it. It would never do to imagine canals crossing the seas.

No great rivers are visible. There is a striking absence of

clouds. The atmosphere of Mars seems as serene as that of Venus

appears to be cloudy. Mists and clouds, however, sometime appear

to veil his face and add to the difficulty of

169

making observations near the limb of the planet. Lowell concludes

it must be a calm and serene atmosphere; probably only

one-seventh of our own in density. The normal height of the

barometer in Mars would then be but four and a half inches. This

is a pressure far less than exists on the top of the highest

terrestrial mountain. A mountain here must have an altitude of

about ten miles to possess so low a pressure on its summit. Drops

of water big enough to form rain can hardly collect in such a

rarefied atmosphere. Moisture will fall as dew or frost upon the

ground. The days will be hot owing to the unimpeded solar

radiation; the nights bitterly cold owing to the free radiation

into space.

We may add that in such a climate the frost will descend

principally upon the high ground at night time and in the

advancing day it will melt. The freer radiation brings about this

phenomenon among our own mountains in clear and calm weather.

With the progressive melting of the snow upon the pole Lowell

connected many phenomena upon the planet's surface of much

interest. The dark spaces appear to grow darker and more

greenish. The canals begin to show themselves and reveal their

double nature. All this suggests that the moisture liberated by

the melting of the polar snow with the advancing year, is

carrying vitality and springtime over the surface of the planet.

But how is the water conveyed?

Lowell believes principally by the canals. These are

170

constructed triangulating the surface of the planet in all

directions. What we see, according to Lowell, is not the canal

itself, but the broad band of vegetation which springs up on the

arrival of the water. This band is perhaps thirty or forty miles

wide, but perhaps much less, for Lowell reports that the better

the conditions of observation the finer the lines appeared, so

that they may be as narrow, possibly, as fifteen miles. It is to

be remarked that a just visible dot on the surface of Mars must

possess a diameter of 30 miles. But a chain of much smaller dots

will be visible, just as we can see such fine objects as spiders'

webs. The widening of the canals is then accounted for, according

to Lowell, by the growth of a band of vegetation, similar to that

which springs into existence when the floods of the Nile irrigate

the plains of Egypt.

If no other explanation of the lines is forthcoming than that

they are the work of intelligence, all this must be remembered.

If all other theories fail us, much must be granted Lowell. We

must not reason like fishes—as Lowell puts it—and deny that

intelligent beings can thrive in an atmospheric pressure of four

and half inches of mercury. Zurbriggen has recently got to the

top of Aconcagua, a height of 24,000 feet. On the summit of such

a mountain the barometer must stand at about ten inches. Why

should not beings be developed by evolution with a lung capacity

capable of living at two and a half times this altitude. Those

steadily

171

curved parallel lines are, indeed, very unlike anything we have

experience of. It would be rather to be expected that another

civilisation than our own would present many wide differences in

its development.

What then is the picture we have before us according to Lowell?

It is a sufficiently dramatic one.

Mars is a world whose water supply, never probably very abundant,

has through countless years been drying up, sinking into his

surface. But the inhabitants are making a brave fight for it,

They have constructed canals right round their world so that the

water, which otherwise would run to waste over the vast deserts,

is led from oasis to oasis. Here the great centres of

civilisation are placed: their Londons, Viennas, New Yorks. These

gigantic works are the works of despair. A great and civilised

world finds death staring it in the face. They have had to triple

their canals so that when the central canal has done its work the

water is turned into the side canals, in order to utilise it as

far as possible. Through their splendid telescopes they must view

our seas and ample rivers; and must die like travellers in the

desert seeing in a mirage the cool waters of a distant lake.

Perhaps that lonely signal reported to have been seen in the

twilight limb of Mars was the outcome of pride in their splendid

and perishing civilisation. They would leave some memory of it:

they would have us witness how great was that civilisation before

they perish!

I close this dramatic picture with the poor comfort

172

that several philanthropic people have suggested signalling to

them as a mark of sympathy. It is said that a fortune was

bequeathed to the French Academy for the purpose of communicating

with the Martians. It has been suggested that we could flash

signals to them by means of gigantic mirrors reflecting the light

of our Sun. Or, again, that we might light bonfires on a

sufficiently large scale. They would have to be about ten miles

in diameter! A writer in the Pall Mall Gazette suggested that

there need really be no difficulty in the matter. With the kind

cooperation of the London Gas Companies (this was before the days

of electric lighting) a signal might be sent without any

additional expense if the gas companies would consent to

simultaneously turn off the gas at intervals of five minutes over

the whole of London, a signal which would be visible to the

astronomers in Mars would result. He adds, naively: "If only

tried for an hour each night some results might be obtained."

II

We have reviewed the theory of the artificial construction of the

Martian lines. The amount of consideration we are disposed to

give to the supposition that there are upon Mars other minds than

ours will—as I have stated—necessarily depend upon whether or not

we can assign a probable explanation of the lines upon purely

physical grounds. If it is apparent that such

173

lines would be formed with great probability under certain

conditions, which conditions are themselves probable, then the

argument by exclusion for the existence of civilisation on Mars,

at once breaks down.

{Fig. 10}

As a romance writer is sometimes under the necessity of

transporting his readers to other scenes, so I must now ask you

to consent to be transported some millions

174

of miles into the region of the heavens which lies outside Mars'

orbit.

Between Mars and Jupiter is a chasm of 341 millions of miles.

This gap in the sequence of planets was long known to be quite

out of keeping with the orderly succession of worlds outward from

the Sun. A society was formed at the close of the last century

for the detection of the missing world. On the first day of the

last century, Piazzi—who, by the way, was not a member of the

society—discovered a tiny world in the vacant gap. Although

eagerly welcomed, as better than nothing, it was a disappointing

find. The new world was a mere rock. A speck of about 160 miles

in diameter. It was obviously never intended that such a body

should have all this space to itself. And, sure enough, shortly

after, another small world was discovered. Then another was

found, and another, and so on; and now more than 400 of these

strange little worlds are known.

But whence came such bodies? The generally accepted belief is

that these really represent a misbegotten world. When the Sun was

younger he shed off the several worlds of our system as so many

rings. Each ring then coalesced into a world. Neptune being the

first born; Mercury the youngest born.

After Jupiter was thrown off, and the Sun had shrunk away inwards

some 20o million miles, he shed off another ring. Meaning that

this offspring of his should grow up like the rest, develop into

a stable world with the

175

potentiality even, it may be, of becoming the abode of rational

beings. But something went wrong. It broke up into a ring of

little bodies, circulating around him.

It is probable on this hypothesis that the number we are

acquainted with does not nearly represent the actual number of

past and present asteroids. It would take 125,000 of the biggest

of them to make up a globe as big as our world. They, so far as

they are known, vary in size from 10 miles to 160 miles in

diameter. It is probable then—on the assumption that this failure

of a world was intended to be about the mass of our Earth—that

they numbered, and possibly number, many hundreds of thousands.

Some of these little bodies are very peculiar in respect to the

orbits they move in. This peculiarity is sometimes in the

eccentricity of their orbits, sometimes in the manner in which

their orbits are tilted to the general plane of the ecliptic, in

which all the other planets move.

The eccentricity, according to Proctor, in some cases may attain

such extremes as to bring the little world inside Mars' mean

distance from the sun. This, as you will remember, is very much

less than his greatest distance from the sun. The entire belt of

asteroids—as known—lie much nearer to Mars than to Jupiter.

As regards the tilt of their orbits, some are actually as much as

34 degrees inclined to the ecliptic, so that in fact they are

seen from the Earth among our polar constellations.

176

From all this you see that Mars occupies a rather hot comer in

the solar system. Is it not possible that more than once in the

remote past Mars may have encountered one of these wanderers? If

he came within a certain distance of the small body his great

mass would sway it from its orbit, and under certain conditions

he would pick up a satellite in this manner. That his present

satellites were actually so acquired is the suggestion of Newton,

of Yale College.

Mars' satellites are indeed suspiciously and most abnormally

small. I have not time to prove this to you by comparison with

the other worlds of the solar system. In fact, they were not

discovered till 1877—although they were predicted in a most

curious manner, with the most uncannily accurate details, by

Swift.

One of these bodies is about 36 miles in diameter. This is

Phobos. Phobos is only 3.700 miles from the surface of Mars. The

other is smaller and further off. He is named Deimos, and his

diameter is only 10 miles. He is 12,500 miles from Mars' surface.

With the exception of Phobos the next smallest satellite known in

the solar system is one of Saturn's—Hyperion; almost 800 miles in

diameter. The inner one goes all round Mars in 7½ hours. This is

Phobos' month. Mars turns on his axis in 24 hours and 40 minutes,

so that people in Mars would see the rise of Phobos twice in the

course of a day and night; lie would apparently cross the sky

177

going against the other satellite; that is, he would move

apparently from west to east.

We may at least assume as probable that other satellites have

been gathered by Mars in the past from the army of asteroids.

Some of the satellites so picked up would be direct: that is,

would move round the planet in the direction of his axial

rotation. Others, on the chances, would be retrograde: that is,

would move against his axial rotation. They would describe orbits

making the same various angles with the ecliptic as do the

asteroids; and we may be sure they would be of the same varying

dimensions.

We go on to inquire what would be the consequence to Mars of such

captures.

A satellite captured in this manner is very likely to be pulled

into the Planet. This is a probable end of a satellite in any

case. It will probably be the end of our satellite too. The

satellite Phobos is indeed believed to be about to take this very

plunge into his planet. But in the case when the satellite picked

up happens to be rotating round the planet in the opposite

direction to the axial rotation of the planet, it is pretty

certain that its career as a satellite will be a brief one. The

reasons for this I cannot now give. If, then, Mars picked up

satellites he is very sure to have absorbed them sooner or later.

Sooner if they happened to be retrograde satellites, later if

direct satellites. His present satellites are recent additions.

They are direct.

178

The path of an expiring satellite will be a slow spiral described

round the planet. The spiral will at last, after many years,

bring the satellite down upon the surface of the primary. Its

final approach will be accelerated if the planet possesses an

atmosphere, as Mars probably does. A satellite of the dimensions

of Phobos—that is 36 miles in diameter—would hardly survive more

than 30 to 60 years within seventy miles of Mars' surface. It

will then be rotating round Mars in an hour and forty minutes,

moving, in fact, at the rate of 2.2 miles per second. In the

course of this 30 or 60 years it will, therefore, get round

perhaps 200,000 times, before it finally crashes down upon the

Martians. During this closing history of the satellite there is

reason to believe, however, that it would by no means pursue

continually the same path over the surface of the planet. There

are many disturbing factors to be considered. Being so small any

large surface features of Mars would probably act to perturb the

orbit of the satellite.

The explanation of Mars' lines which I suggest, is that they were

formed by the approach of such satellites in former times. I do

not mean that they are lines cut into his surface by the actual

infall of a satellite. The final end of the satellite would be

too rapid for this, I think. But I hope to be able to show you

that there is reason to believe that the mere passage of the

satellite, say at 70 miles above the surface of the planet, will,

in itself, give rise to effects on the crust of the planet

capable

179

of accounting for just such single or parallel lines as we see.

In the first place we have to consider the stability of the

satellite. Even in the case of a small satellite we cannot

overlook the fact that the half of the satellite near the planet

is pulled towards the planet by a gravitational force greater

than that attracting the outer half, and that the centrifugal

force is less on the inner than on the outer hemisphere. Hence

there exists a force tending to tear the satellite asunder on the

equatorial section tangential

{Fig. 11}

to the planet's surface. If in a fluid or plastic state, Phobos,

for instance, could not possibly exist near the planet's surface.

The forces referred to would decide its fate. It may be shown by

calculation, however, that if Phobos has the strength of basalt

or glass there would remain a considerable coefficient of safety

in favour of the satellite's stability; even when the surfaces of

planet and satellite were separated by only five miles.

We have now to consider some things which we expect will happen

before the satellite takes its final plunge into the planet.

180

This diagram (Fig. 11) shows you the satellite travelling above

the surface of the planet. The satellite is advancing towards, or

away from, the spectator. The planet is supposed to show its

solid crust in cross section, which may be a few miles in

thickness. Below this is such a hot plastic magma as we have

reason to believe underlies much of the solid crust of our own

Earth. Now there is an attraction between the satellite and the

crust of the planet; the same gravitational attraction which

exists between every particle of matter in the universe. Let us

consider how this attraction will affect the planet's crust. I

have drawn little arrows to show how we may consider the

attraction of the satellite pulling the crust of the planet not

only upwards, but also pulling it inwards beneath the satellite.

I have made these arrows longer where calculation shows the

stress is greater. You see that the greatest lifting stress is

just beneath the satellite, whereas the greatest stress pulling

the crust in under the satellite is at a point which lies out

from under the satellite, at a considerable distance. At each

side of the satellite there is a point where the stress pulling

on the crust is the greatest. Of the two stresses the lifting

stress will tend to raise the crust a little; the pulling stress

may in certain cases actually tear the crust across; as at A and

B.

It is possible to calculate the amount of the stress at the point

at each side of the satellite where the stress is at its

greatest. We must assume the satellite to be a certain size and

density; we must also assume the crust of

181

Mars to be of some certain density. To fix our ideas on these

points I take the case of the present satellite Phobos. What

amount of stress will he exert upon the crust of Mars when he

approaches within, say, 40 miles of the planet's surface? We know

his size approximately—he is about 36 miles in diameter. We can

guess his density to be between four times that of water and

eight times that of water. We may assume the density of Mars'

surface to be about the same as that of our Earth's surface, that

is three times as dense as water. We now find that the greatest

stress tending to rend open the surface crust of Mars will be

between 4,000 and 8,000 pounds to the square foot according to

the density we assign to Phobos.

Will such a stress actually tear open the crust? We are not able

to answer this question with any certainty. Much will depend upon

the nature and condition of the crust. Thus, suppose that we are

here (Fig. 12) looking down upon the satellite which is moving

along slowly relatively to Mars' surface, in the direction of the

arrow. The satellite has just passed over a weak and cracked part

of the planet's crust. Here the stress has been sufficient to

start two cracks. Now you know how easy it is to tear a piece of

cloth when you go to the edge of it in order to make a beginning.

Here the stress from the satellite has got to the edge of the

crust. It is greatly concentrated just at the extremities of the

cracks. It will, unler such circumstances probably carry on the

182

tear. If it does not do so this time, remember the satellite will

some hours later be coming over the same place again, and then

again for, at least, many hundreds of times. Then also we are not

limited to the assumption that the

{Fig. 12}

satellite is as small as Phobos. Suppose we consider the case of

a satellite approaching Mars which has a diameter double that of

Phobos; a diameter still much less than that of the larger class

of asteroids. Even at the distance

183

of 65 miles the stress will now amount to as much as from 15 to

30 tons per square foot. It is almost certain that such a stress

repeated a comparatively few times over the same parts of the

planet's surface would so rend the crust as to set up lines along

which plutonic action would find a vent. That is, we might expect

along these lines all the phenomena of upheaval and volcanic

eruption which give rise to surface elevations.

The probable effect of a satellite of this dimension travelling

slowly relatively to the surface of Mars is, then, to leave a

very conspicuous memorial of his presence behind him. You see

from the diagram that this memorial will consist o: two parallel

lines of disturbance.

The linear character of the gravitational effects of the

satellite is due entirely to the motion of the satellite

relatively to the surface of the planet. If the satellite stood

still above the surface the gravitational stress in the crust

would, of course, be exerted radially outwards from the centre of

the satellite. It would attain at the central point beneath the

satellite its maximum vertical effect, and at some radial

distance measured outwards from this point, which distance we can

calculate, its maximum horizontal tearing effect. When the

satellite moves relatively to the planet's crust, the horizontal

tearing force acts differently according to whether it is

directed in the line of motion or at right angles to this line.

In the direction of motion we see that the satellite

184

creates as it passes over the crust a wave of rarefaction or

tension as at D, followed by compression just beneath the

satellite and by a reversed direction of gravitational pull as

the satellite passes onwards. These stresses rapidly replace one

another as the satellite travels along. They are resisted by the

inertia of the crust, and are taken up by its elasticity. The

nature of this succession of alternate compressions and

rarefactions in the crust possess some resemblance to those

arising in an earthquake shock.

If we consider the effects taking place laterally to the line of

motion we see that there are no such changes in the nature of the

forces in the crust. At each passage of the satellite the

horizontal tearing stress increases to a maximum, when it is

exerted laterally, along the line passing through the horizontal

projection of the satellite and at right angles to the line of

motion, and again dies away. It is always a tearing stress,

renewed again and again.

This effect is at its maximum along two particular parallel lines

which are tangents to the circle of maximum horizontal stress and

which run parallel with the path of the satellite. The distance

separating these lines depend upon the elevation of the satellite

above the planet's surface. Such lines mark out the theoretical

axes of the "double canals" which future crustal movements will

more fully develop.

It is interesting to consider what the effect of such

185

conditions would be if they arose at the surface of our own

planet. We assume a horizontal force in the crust adequate to set

up tensile stresses of the order, say, of fifteen tons to the

square foot and these stresses to be repeated every few hours;

our world being also subject to the dynamic effects we recognise

in and beneath its crust.

It is easy to see that the areas over which the satellite exerted

its gravitational stresses must become the foci —foci of linear

form—of tectonic developments or crust movements. The relief of

stresses, from whatever cause arising, in and beneath the crust

must surely take place in these regions of disturbance and along

these linear areas. Here must become concentrated the folding

movements, which are under existing conditions brought into the

geosynclines, along with their attendant volcanic phenomena. In

the case of Mars such a concentration of tectonic events would

not, owing to the absence of extensive subaerial denudation and

great oceans, be complicated by the existence of such synclinal

accumulations as have controlled terrestrial surface development.

With the passage of time the linear features would probably

develop; the energetic substratum continually asserting its

influence along such lines of weakness. It is in the highest

degree probable that radioactivity plays no less a part in

Martian history than in terrestrial. The fact of radioactive

heating allows us to assume the thin surface crust and continued

sub-crustal energy throughout the entire period of the planet's

history.

186

How far willl these effects resemble the double canals of Mars?

In this figure and in the calculations I have given you I have

supposed the satellite engaged in marking the planet's surface

with two lines separated by about the interval separating the

wider double canals of Mars—that is about 220 miles apart. What

the distance between the lines will be, as already stated, will

depend upon the height of the satellite above the surface when it

comes upon a part of the crust in a condition to be affected by

the stresses it sets up in it. If the satellite does its work at

a point lower down above the surface the canal produced will be

narrower. The stresses, too, will then be much greater. I must

also observe that once the crust has yielded to the pulling

stress, there is great probability that in future revolutions of

the satellite a central fracture will result. For then all the

pulling force adds itself to the lifting force and tends to crush

the crust inwards on the central line beneath the satellite. It

is thus quite possible that the passage of a satellite may give

rise to triple lines. There is reason to believe that the canals

on Mars are in some cases triple.

I have spoken all along of the satellite moving slowly over the

surface of Mars. I have done so as I cannot at all pronounce so

readily on what will happen when the satellite's velocity over

the surface of Mars is very great. To account for all the lines

mapped by Lowell some of them must have been produced by

satellities moving relatively to the surface of Mars at

velocities so great

187

as three miles a second or even rather more. The stresses set up

are, in such cases, very difficult to estimate. It has not yet

been done. Parallel lines of greatest stress or impulse ought to

be formed as in the other case.

I now ask your attention to another kind of evidence that the

lines are due in some way to the motion of satellites passing

over the surface of Mars.

I may put the fresh evidence to which I refer, in this way: In

Lowell's map (P1. XXII, p. 192), and in a less degree in

Schiaparelli's map (ante p. 166), we are given the course of the

lines as fragments of incomplete curves. Now these curves might

have been anything at all. We must take them as they are,

however, when we apply them as a test of the theory that the

motion of a satellite round Mars can strike such lines. If it can

be shown that satellites revolving round Mars might strike just

such curves then we assume this as an added confirmation of the

hypothesis.

We must begin by realising what sort of curves a satellite which

disturbs the surface of a planet would leave behind it after its

demise. You might think that the satellite revolving round and

round the planet must simply describe a circle upon the spherical

surface of the planet: a "great circle" as it is called; that is

the greatest circle which can be described upon a sphere. This

great circle can, however, only be struck, as you will see, when

the planet is not turning upon its axis: a condition not likely

to be realised.

This diagram (PI. XXI) shows the surface of a globe

188

covered with the usual imaginary lines of latitude and longitude.

The orbit of a supposed satellite is shown by a line crossing the

sphere at some assumed angle with the equator. Along this line

the satellite always moves at uniform velocity, passing across

and round the back of the sphere and again across. If the sphere

is not turning on its polar axis then this satellite, which we

will suppose armed with a pencil which draws a line upon the

sphere, will strike a great circle right round the sphere. But

the sphere is rotating. And it is to be expected that at

different times in a planet's history the rate of rotation varies

very much indeed. There is reason to believe that our own day was

once only 2½ hours long, or thereabouts. After a preliminary rise

in velocity of axial rotation, due to shrinkage attending rapid

cooling, a planet as it advances in years rotates slower and

slower. This phenomenon is due to tidal influences of the sun or

of satellites. On the assumption that satellites fell into Mars

there would in his case be a further action tending to shorten

his day as time went on.

The effect of the rotation of the planet will be, of course, that

as the satellite advances with its pencil it finds the surface of

the sphere being displaced from under it. The line struck ceases

to be the great circle but wanders off in another curve—which is

in fact not a circle at all.

You will readily see how we find this curve. Suppose the sphere

to be rotating at such a speed that while the satellite is

advancing the distance _Oa_, the point _b_ on the

189

sphere will be carried into the path of the satellite. The pencil

will mark this point. Similarly we find that all the points along

this full curved line are points which will just find themselves

under the satellite as it passes with its pencil. This curve is

then the track marked out by the revolving satellite. You see it

dotted round the back of the sphere to where it cuts the equator

at a certain point. The course of the curve and the point where

it cuts the equator, before proceeding on its way, entirely

depend upon the rate at which we suppose the sphere to be

rotating and the satellite to be describing the orbit. We may

call the distance measured round the planet's equator separating

the starting point of the curve from the point at which it again

meets the equator, the "span" of the curve. The span then depends

entirely upon the rate of rotation of the planet on its axis and

of the satellite in its orbit round the planet.

But the nature of events might have been somewhat different. The

satellite is, in the figure, supposed to be rotating round the

sphere in the same direction as that in which the sphere is

turning. It might have been that Mars had picked up a satellite

travelling in the opposite direction to that in which he was

turning. With the velocity of planet on its axis and of satellite

in its orbit the same as before, a different curve would have

been described. The span of the curve due to a retrograde

satellite will be greater than that due to a direct satellite.

The retrograde satellite will have a span more than half

190

way round the planet, the direct satellite will describe a curve

which will be less than half way round the planet: that is a span

due to a retrograde satellite will be more than 180 degrees,

while the span due to a direct satellite will be less than 180

degrees upon the planet's equator.

I would draw your attention to the fact that what the span will

be does not depend upon how much the orbit of the satellite is

inclined to the equator. This only decides how far the curve

marked out by the satellite will recede from the equator.

We find then, so far, that it is easy to distinguish between the

direct and the retrograde curves. The span of one is less, of the

other greater, than 180 degrees. The number of degrees which

either sort of curve subtends upon the equator entirely depends

upon the velocity of the satellite and the axial velocity of the

planet.

But of these two velocities that of the satellite may be taken as

sensibly invariable, when close enough to use his pencil. This

depends upon the law of centrifugal force, which teaches us that

the mass of the planet alone decides the velocity of a satellite

in its orbit at any fixed distance from the planet's centre. The

other velocity—that of the planet upon its axis—was, as we have

seen, not in the past what it is now. If then Mars, at various

times in his past history, picked up satellites, these satellites

will describe curves round him having different spans which will

depend upon the velocity of axial rotation of Mars at the time

and upon this only.

191

In what way now can we apply this knowledge of the curves

described by a satellite as a test of the lunar origin of the

lines on Mars?

To do this we must apply to Lowell's map. We pick out preferably,

of course, the most complete and definite curves. The chain of

canals of which Acheron and Erebus are members mark out a fairly

definite curve. We produce it by eye, preserving the curvature as

far as possible, till it cuts the equator. Reading the span on

the equator we find' it to be 255 degrees. In the first place we

say then that this curve is due to a retrograde satellite. We

also note on Lowell's map that the greatest rise of the curve is

to a point about 32 degrees north of the equator. This gives the

inclination of the satellite's orbit to the plane of Mars'

equator.

With these data we calculate the velocity which the planet must

have possessed at the time the canal was formed on the hypothesis

that the curve was indeed the work of a satellite. The final

question now remains If we determine the curve due to this

velocity of Mars on its axis, will this curve fit that one which

appears on Lowell's map, and of which we have really availed

ourselves of only three points? To answer this question we plot

upon a sphere, the curve of a satellite, in the manner I have

described, assigning to this sphere the velocity derived from the

span of 255 degrees. Having plotted the curve on the sphere it

only remains to transfer it to Lowell's map. This is easily

done.

192

This map (Pl. XXII) shows you the result of treating this, as

well as other curves, in the manner just described. You see that

whether the fragmentary curves are steep and receding far from

the equator; or whether they are flat and lying close along the

equator; whether they span less or more than 180 degrees; the

curves determined on the supposition that they are the work of

satellites revolving round Mars agree with the mapped curves;

following them with wonderful accuracy; possessing their

properties, and, indeed, in some cases, actually coinciding with

them.

I may add that the inadmissible span of 180 degrees and spans

very near this value, which are not well admissible, are so far

as I can find, absent. The curves are not great circles.

You will require of me that I should explain the centres of

radiation so conspicuous here and there on Lowell's map. The

meeting of more than two lines at the oases is a phenomenon

possibly of the same nature and also requiring explanation.

In the first place the curves to which I have but briefly

referred actually give rise in most cases to nodal, or crossing

points; sometimes on the equator, sometimes off the equator;

through which the path of the satellite returns again and again.

These nodal points will not, however, afford a general

explanation of the many-branched radiants.

It is probable that we should refer such an appearance

193

as is shown at the Sinus Titanum to the perturbations of the

satellite's path due to the surface features on Mars. Observe

that the principal radiants are situated upon the boundary of the

dark regions or at the oases. Higher surface levels may be

involved in both cases. Some marked difference in topography must

characterise both these features. The latter may possibly

originate in the destruction of satellites. Or again, they may

arise in crustal disturbance of a volcanic nature, primarily

induced or localised by the crossing of two canals. Whatever the

origin of these features it is only necessary to assume that they

represent elevated features of some magnitude to explain the

multiplication of crossing lines. We must here recall what

observers say of the multiplicity of the canals. According to

Lowell, "What their number maybe lies quite beyond the

possibility of count at present; for the better our own air, the

more of them are visible."

Such innumerable canals are just what the present theory

requires. An in-falling satellite will, in the course of the last

60 or 80 years of its career, circulate some 100,000 times over

Mars' surface. Now what will determine the more conspicuous

development of a particular canal? The mass of the satellite; the

state of the surface crust; the proximity of the satellite; and

the amount of repetition over the same ground. The after effects

may be taken as proportional to the primary disturbance.

194

It is probable that elevated surface features will influence two

of these conditions: the number of repetitions and the proximity

to the surface. A tract 100 miles in diameter and elevated 5,000

or 10,000 feet would seriously perturb the orbit of such a body as

Phobos. It is to be expected that not only would it be effective

in swaying the orbit of the satellite in the horizontal direction

but also would draw it down closer to the surface. It is even to

be considered if such a mass might not become nodal to the

satellite's orbit, so that this passed through or above this

point at various inclinations with its primary direction. If

acting to bring down the orbit then this will quicken the speed

and cause the satellite further on its path to attain a somewhat

higher elevation above the surface. The lines most conspicuous in

the telescope are, in short, those which have been favoured by a

combination of circumstances as reviewed above, among which

crustal features have, in some cases, played a part.

I must briefly refer to what is one of the most interesting

features of the Martian lines: the manner in which they appear to

come and go like visions.

Something going on in Mars determines the phenomenon. On a

particular night a certain line looks single. A few nights later

signs of doubling are perceived, and later still, when the seeing

is particularly good, not one but two lines are seen. Thus, as an

example, we may take the case of Phison and Euphrates. Faint

glimpses of the dual state were detected in the summer

195

and autumn, but not till November did they appear as distinctly

double. Observe that by this time the Antarctic snows had melted,

and there was in addition, sufficient time for the moisture so

liberated to become diffused in the planet's atmosphere.

This increase in the definition and conspicuousness of certain

details on Mars' surface is further brought into connection with

the liberation of the polar snows and the diffusion of this water

through the atmosphere, by the fact that the definition appeared

progressively better from the south pole upwards as the snow

disappeared. Lowell thinks this points to vegetation springing up

under the influence of moisture; he considers, however, as we

have seen, that the canals convey the moisture. He has to assume

the construction of triple canals to explain the doubling of the

lines.

If we once admit the canals to be elevated ranges—not necessarily

of great height—the difficulty of accounting for increased

definition with increase of moisture vanishes. We need not

necessarily even suppose vegetation concerned. With respect to

this last possibility we may remark that the colour observations,

upon which the idea of vegetation is based, are likely to be

uncertain owing to possible fatigue effects where a dark object

is seen against a reddish background.

However this may be we have to consider what the effects of

moisture increasing in the atmosphere of Mars will be with regard

to the visibility of elevated ranges,

196

We assume a serene and rare atmosphere: the nights intensely

cold, the days hot with the unveiled solar radiation. On the hill

tops the cold of night will be still more intense and so, also,

will the solar radiation by day. The result of this state of

things will be that the moisture will be precipitated mainly on

the mountains during the cold of night—in the form of frost—and

during the day this covering of frost will melt; and, just as we

see a heavy dew-fall darken the ground in summer, so the melting

ice will set off the elevated land against the arid plains below.

Our valleys are more moist than our mountains only because our

moisture is so abundant that it drains off the mountains into the

valleys. If moisture was scarce it would distil from the plains

to the colder elevations of the hills. On this view the

accentuation of a canal is the result of meteorological effects

such as would arise in the Martian climate; effects which must be

influenced by conditions of mountain elevation, atmospheric

currents, etc. We, thus, follow Lowell in ascribing the

accentuation of the canals to the circulation of water in Mars;

but we assume a simple and natural mode of conveyance and do not

postulate artificial structures of all but impossible magnitude.

That vegetation may take part in the darkening of the elevated

tracts is not improbable. Indeed we would expect that in the

Martian climate these tracts would be the only fertile parts of

the surface.

Clouds also there certainly are. More recent observations

197

appear to have set this beyond doubt. Their presence obviously

brings in other possible explanations of the coming and going of

elevated surface features.

Finally, we may ask what about the reliability of the maps? About

this it is to be said that the most recent map—that by Lowell—has

been confirmed by numerous drawings by different observers, and

that it is,itself the result of over 900 drawings. It has become

a standard chart of Mars, and while it would be rash to contend

for absence of errors it appears certain that the trend of the

principal canals may be relied on, as, also, the general features

of the planet's surface.

The question of the possibility of illusion has frequently been

raised. What I have said above to a great extent answers such

objections. The close agreement between the drawings of different

observers ought really to set the matter at rest. Recently,

however, photography has left no further room for scepticism.

First photographed in 1905, the planet has since been

photographed many thousands of times from various observatories.

A majority of the canals have been so mapped. The doubling of the

canals is stated to have been also so recorded.[1]

The hypothesis which I have ventured to put before you involves

no organic intervention to account for the

[1] E. C. Slipher's paper in _Popular Astronomy_ for March, 1914,

gives a good account of the recent work.

198

details on Mars' surface. They are physical surface features.

Mars presents his history written upon his face in the scars of

former encounters—like the shield of Sir Launcelot. Some of the

most interesting inferences of mathematical and physical

astronomy find a confirmation in his history. The slowing down in

the rate of axial rotation of the primary; the final inevitable

destruction of the satellite; the existence in the past of a far

larger number of asteroids than we at present are acquainted

with; all these great facts are involved in the theory now

advanced. If justifiably, then is Mars' face a veritable

Principia.

To fully answer the question which heads these lectures, we

should go out into the populous solitudes (if the term be

permitted) which lie beyond our system. It is well that there is

now no time left to do so; for, in fact, there we can only dream

dreams wherein the limits of the possible and the impossible

become lost.

The marvel of the infinite number of stars is not so marvellous

as the rationality that fain would comprehend them. In seeking

other minds than ours we seek for what is almost infinitely

complex and coordinated in a material universe relatively simple

and heterogeneous. In our mental attitude towards the great

question, this fact must be regarded as fundamental.

I can only fitly close a discourse which has throughout weighed

the question of the living thought against the unthinking laws of

matter, by a paraphrase of the words

199

of a great poet when he, in higher and, perhaps, more philosophic

language, also sought to place the one in comparison with the

other.[1]

Richter thought that he was—with his human heart

unstrengthened—taken by an angel among the universe of stars.

Then, as they journeyed, our solar system was sunken like a faint

star in the abyss, and they travelled yet further, on the wings

of thought, through mightier systems: through all the countless

numbers of our galaxy. But at length these also were left behind,

and faded like a mist into the past. But this was not all. The

dawn of other galaxies appeared in the void. Stars more countless

still with insufferable light emerged. And these also were

passed. And so they went through galaxies without number till at

length they stood in the great Cathedral of the Universe. Endless

were the starry aisles; endless the starry columns; infinite the

arches and the architraves of stars. And the poet saw the mighty

galaxies as steps descending to infinity, and as steps going up

to infinity.

Then his human heart fainted and he longed for some narrow cell;

longed to lie down in the grave that he might hide from infinity.

And he said to the angel:

"Angel, I can go with thee no farther. Is there, then, no end to

the universe of stars?"

[1] De Quincy in his _System of the Heavens_ gives a fine

paraphrase of "Richter's Dream."

200

Then the angel flung up his glorious hands to the heaven of

heavens, saying "End is there none to the universe of God? Lo!

also there is no beginning."

201

THE LATENT IMAGE [1]

My inclination has led me, in spite of a lively dread of

incurring a charge of presumption, to address you principally on

that profound and most subtle question, the nature and mode of

formation of the photographic image. I am impelled to do so, not

only because the subject is full of fascination and hopefulness,

but because the wide topics of photographic methods or

photographic applications would be quite unfittingly handled by

the president you have chosen.

I would first direct your attention to Sir James Dewar's

remarkable result that the photographic plate retains

considerable power of forming the latent image at temperatures

approaching the absolute zero—a result which, as I submit,

compels us to regard the fundamental effects progressing in the

film under the stimulus of light undulations as other than those

of a purely chemical nature. But few, if any, instances of

chemical combination or decomposition are known at so low a

temperature. Purely chemical actions cease, indeed, at far higher

temperatures, fluorine being among the few bodies which still

show

[1] Presidential address to the Photographic Convention of the

United Kingdom, July, 1905. _Nature_, Vol. 72, p. 308.

202

chemical activity at the comparatively elevated temperature of

-180° C. In short, this result of Sir James Dewar's suggests that

we must seek for the foundations of photographic action in some

physical or intra-atomic effect which, as in the case of

radioactivity or fluorescence, is not restricted to intervals of

temperature over which active molecular vis viva prevails. It

compels us to regard with doubt the role of oxidation or other

chemical action as essential, but rather points to the view that

such effects must be secondary or subsidiary. We feel, in a word,

that we must turn for guidance to some purely photo-physical

effect.

Here, in the first place, we naturally recall the views of Bose.

This physicist would refer the formation of the image to a strain

of the bromide of silver molecule under the electric force in the

light wave, converting it into what might be regarded as an

allotropic modification of the normal bromide which subsequently

responds specially to the attack of the developer. The function

of the sensitiser, according to this view, is to retard the

recovery from strain. Bose obtained many suggestive parallels

between the strain phenomena he was able to observe in silver and

other substances under electromagnetic radiation and the

behaviour of the photographic plate when subjected to

long-continued exposure to light.

This theory, whatever it may have to recommend it, can hardly be

regarded as offering a fundamental explanation. In the first

place, we are left in the dark as to what

203

the strain may be. It may mean many and various things. We know

nothing as to the inner mechanism of its effects upon subsequent

chemical actions—or at least we cannot correlate it with what is

known of the physics of chemical activity. Finally, as will be

seen later, it is hardly adequate to account for the varying

degrees of stability which may apparently characterise the latent

image. Still, there is much in Bose's work deserving of careful

consideration. He has by no means exhausted the line of

investigation he has originated.

Another theory has doubtless been in the minds of many. I have

said we must seek guidance in some photo-physical phenomenon.

There is one such which preeminently connects light and chemical

phenomena through the intermediary of the effects of the former

upon a component part of the atom. I refer to the phenomena of

photo-electricity.

It was ascertained by Hertz and his immediate successors that

light has a remarkable power of discharging negative

electrification from the surface of bodies—especially from

certain substances. For long no explanation of the cause of this

appeared. But the electron—the ubiquitous electron—is now known

with considerable certainty to be responsible. The effect of the

electric force in the light wave is to direct or assist the

electrons contained in the substance to escape from the surface

of the body. Each electron carries away a very small charge of

negative electrification. If, then, a body is

204

originally charged negatively, it will be gradually discharged by

this convective process. If it is not charged to start with, the

electrons will still be liberated at the surface of the body, and

this will acquire a positive charge. If the body is positively

charged at first, we cannot discharge it by illumination.

It would be superfluous for me to speak here of the nature of

electrons or of the various modes in which their presence may be

detected. Suffice it to say, in further connection with the Hertz

effect, that when projected among gaseous molecules the electron

soon attaches itself to one of these. In other words, it ionises

a molecule of the gas or confers its electric charge upon it. The

gaseous molecule may even be itself disrupted by impact of the

electron, if this is moving fast enough, and left bereft of an

electron.

We must note that such ionisation may be regarded as conferring

potential chemical properties upon the molecules of the gas and

upon the substance whence the electrons are derived. Similar

ionisation under electric forces enters, as we now believe, into

all the chemical effects progressing in the galvanic cell, and,

indeed, generally in ionised solutes.

An experiment will best illustrate the principles I wish to

remind you of. A clean aluminium plate, carefully insulated by a

sulphur support, is faced by a sheet of copper-wire-gauze placed

a couple of centimetres away from it. The gauze is maintained at

a high positive

205

potential by this dry pile. A sensitive gold-leaf electroscope is

attached to the aluminium plate, and its image thrown upon the

screen. I now turn the light from this arc lamp upon the wire

gauze, through which it in part passes and shines upon the

aluminium plate. The electroscope at once charges up rapidly.

There is a liberation of negative electrons at the surface of the

aluminium; these, under the attraction of the positive body, are

rapidly removed as ions, and the electroscope charges up

positively.

Again, if I simply electrify negatively this aluminium plate so

that the leaves of the attached electroscope diverge widely, and

now expose it to the rays from the arc lamp, the charge, as you

see, is very rapidly dissipated. With positive electrification of

the aluminium there is no effect attendant on the illumination.

Thus from the work of Hertz and his successors we know that

light, and more particularly what we call actinic light, is an

effective means of setting free electrons from certain

substances. In short, our photographic agent, light, has the

power of expelling from certain substances the electron which is

so potent a factor in most, if not in all, chemical effects. I

have not time here to refer to the work of Elster and Geitel

whereby they have shown that this action is to be traced to the

electric force in the light wave, but must turn to the probable

bearing of this phenomenon on the familiar facts of photography.

I assume that the experiment I have shown you is the most

206

fundamental photographic experiment which it is now in our power

to make.

We must first ask from what substances can light liberate

electrons. There are many—metals as well as non-metals and

liquids. It is a very general phenomenon and must operate widely

throughout nature. But what chiefly concerns the present

consideration is the fact that the haloid salts of silver are

vigorously photo-electric, and, it is suggestive, possess,

according to Schmidt, an activity in the descending order

bromide, chloride, iodide. This is, in other words, their order

of activity as ionisers (under the proper conditions) when

exposed to ultra-violet light. Photographers will recognise that

this is also the order of their photographic sensitiveness.

Another class of bodies also concerns our subject: the special

sensitisers used by the photographer to modify the spectral

distribution of sensibility of the haloid salts, _e.g._ eosine,

fuchsine, cyanine. These again are electron-producers under light

stimulus. Now it has been shown by Stoletow, Hallwachs, and

Elster and Geitel that there is an intimate connection between

photo-electric activity and the absorption of light by the

substance, and, indeed, that the particular wave-lengths absorbed

by the substance are those which are effective in liberating the

electrons. Thus we have strong reason for believing that the

vigorous photo-electric activity displayed by the special

sensitisers must be dependent upon their colour absorption. You

will recognise that this is just

207

the connection between their photographic effects and their

behaviour towards light.

There is yet another suggestive parallel. I referred to the

observation of Sir James Dewar as to the continued sensitiveness

of the photographic film at the lowest attained extreme of

temperature, and drew the inference that the fundamental

photographic action must be of intra-atomic nature, and not

dependent upon the vis viva of the molecule or atom. In then

seeking the origin of photographic action in photo-electric

phenomena we naturally ask, Are these latter phenomena also

traceable at low temperatures? If they are, we are entitled to

look upon this fact as a qualifying characteristic or as another

link in the chain of evidence connecting photographic with

photo-electric activity.

I have quite recently, with the aid of liquid air supplied to me

from the laboratory of the Royal Dublin Society, tested the

photo-sensibility of aluminium and also of silver bromide down to

temperatures approaching that of the liquid air. The mode of

observation is essentially that of Schmidt—what he terms his

static method. The substance undergoing observation is, however,

contained at the bottom of a thin copper tube, 5 cm. in diameter,

which is immersed to a depth of about 10 cm in liquid air. The

tube is closed above by a paraffin stopper which carries a thin

quartz window as well as the sulphur tubes through which the

connections pass. The air within is very carefully dried by

phosphorus

208

pentoxide before the experiment. The arc light is used as source

of illumination. It is found that a vigorous photo-electric

effect continues in the case of the clean aluminium. In the case

of the silver bromide a distinct photo-electric effect is still

observed. I have not had leisure to make, as yet, any trustworthy

estimate of the percentage effect at this temperature in the case

of either substance. Nor have I determined the temperature

accurately. The latter may be taken as roughly about -150° C,

Sir James Dewar's actual measilrements afforded twenty per cent.

of the normal photographic effect at -180° C. and ten per cent.

at the temperature of -252.5° C.

With this much to go upon, and the important additional fact that

the electronic discharge—as from the X-ray tube or from

radium—generates the latent image, I think we are fully entitled

to suggest, as a legitimate lead to experiment, the hypothesis

that the beginnings of photographic action involve an electronic

discharge from the light-sensitive molecule; in other words that

the latent image is built up of ionised atoms or molecules the

result of the photo-electric effect on the illuminated silver

haloid, and it is upon these ionised atoms that the chemical

effects of the developer are subsequently directed. It may be

that the liberated electrons ionise molecules not directly

affected, or it may be that in their liberation they disrupt

complex molecules built up in the ripening of the

209

emulsion. With the amount we have to go upon we cannot venture to

particularise. It will be said that such an action must be in

part of the nature of a chemical effect. This must be admitted,

and, in so far as the rearrangement of molecular fabrics is

involved, the result will doubtless be controlled by temperature

conditions. The facts observed by Sir James Dewar support this.

But there is involved a fundamental process—the liberation of the

electron by the electric force in the light wave, which is a

physical effect, and which, upon the hypothesis of its reality as

a factor in forming the latent image, appears to explain

completely the outstanding photographic sensitiveness of the film

at temperatures far below those at which chemical actions in

general cease.

Again, we may assume that the electron—producing power of the

special sensitiser or dye for the particular ray it absorbs is

responsible, or responsible in part, for the special

sensitiveness it confers upon the film. Sir Wm. Abney has shown

that these sensitisers are active even if laid on as a varnish on

the sensitive surface and removed before development. It must be

remembered, however, that at temperatures of about -50° these

sensitisers lose much of their influence on the film; as I have

pointed out in a paper read before the Photographic Convention of

1894.

It. appears to me that on these views the curious phenomenon of

recurrent reversals does not present a problem hopeless of

explanation. The process of photo-

210

ionisation constituting the latent image, where the ion is

probably not immediately neutralised by chemical combination,

presents features akin to the charging of a capacity—say a Leyden

jar. There may be a rising potential between the groups of ions

until ultimately a point is attained when there is a spontaneous

neutralisation. I may observe that the phenomena of reversal

appear to indicate that the change in the silver bromide

molecule, whatever be its nature, is one of gradually increasing

intensity, and finally attains a maximum when a return to the

original condition occurs. The maximum is the point of most

intense developable image. It is probable that the sensitiser—in

this case the gelatin in which the bromide of silver is

immersed—plays a part in the conditions of stability which are

involved.

Of great interest in all our considerations and theories is the

recent work of Wood on photographic reversal. The result of this

work is—as I take it—to show that the stability of the latent

image may be very various according to the mode of its formation.

Thus it appears that the sort of latent effect which is produced

by pressure or friction is the least stable of any. This may be

reversed or wiped out by the application of any other known form

of photographic stimulus. Thus an exposure to X-rays will

obliterate it, or a very brief exposure to light. The latent

image arising from X-rays is next in order of increasing

stability. Light action will remove this. Third in order is a

very brief light-shock or sudden flash. This

211

cannot be reversed by any of the foregoing modes of stimulation,

but a long-continued undulatory stimulus, as from lamp-light,

will reverse it. Last and most stable of all is the gradually

built-up configuration due to long-continued light exposure. This

can only be reversed by overdoing it according to the known facts

of recurrent reversal. Wood takes occasion to remark that these

phenomena are in bad agreement with the strain theory of Bose. We

have, in fact, but the one resource—the allotropic modification

of the haloid—whereby to explain all these orders of stability.

It appears to me that the elasticity of the electronic theory is

greater. The state of the ionised system may be very various

according as it arises from continued rhythmic effects or from

unorganised shocks. The ionisation due to X-rays or to friction

will probably be quite unorganised, that due to light more or

less stable according to the gradual and gentle nature of the

forces at work. I think we are entitled to conclude that on the

whole there is nothing in Wood's beautiful experiments opposed to

the photo-electric origin of photographic effects, but that they

rather fall in with what might be anticipated according to that

theory.

When we look for further support to the views I have laid before

you we are confronted with many difficulties. I have not as yet

detected any electronic discharge from the film under light

stimulus. This may be due to my defective experiments, or to a

fact noted by Elster and Geitel concerning the photo-electric

properties of gelatin.

212

They obtained a vigorous effect from Balmain's luminous paint,

but when this was mixed in gelatin there was no external effect.

Schmidt's results as to the continuance of photo-electric

activity when bodies in general are dissolved in each other lead

us to believe that an actual conservative property of the medium

and not an effect of this on the luminous paint is here involved.

This conservative effect of the gelatin may be concerned with its

efficacy as a sensitiser.

In the views I have laid before you I have endeavoured to show

that the recent addition to our knowledge of the electron as an

entity taking part in many physical and chemical effects should

be kept in sight in seeking an explanation of the mode of origin

of the latent image.[1]

[1] For a more detailed account of the subject, and some

ingenious extensions of the views expressed above, see

_Photo-Electricity_, by H. Stanley Allen: Longmans, Green & Ca.,

1913.

213

PLEOCHROIC HALOES [1]

IT is now well established that a helium atom is expelled from

certain of the radioactive elements at the moment of

transformation. The helium atom or alpha ray leaves the

transforming atom with a velocity which varies in the different

radioactive elements, but which is always very great, attaining

as much as 2 x 109 cms. per second; a velocity which, if

unchecked, would carry the atom round the earth in less than two

seconds. The alpha ray carries a positive charge of double the

ionic amount.

When an alpha ray is discharged from the transforming element

into a gaseous medium its velocity is rapidly checked and its

energy absorbed. A certain amount of energy is thus transferred

from the transforming atom to the gas. We recognise this energy

in the gas by the altered properties of the latter; chiefly by

the fact that it becomes a conductor of electricity. The

mechanism by which this change is effected is in part known. The

atoms of the gas, which appear to be freely penetrated by the

alpha ray, are so far dismembered as to yield charged electrons

or ions; the atoms remaining charged with an equal and opposite

charge. Such a medium of

[1] Being the Huxley Lecture, delivered at the University of

Birmingham on October 30th, 1912. Bedrock, Jan., 1913.

214

free electric charges becomes a conductor of electricity by

convection when an electromotive force is applied. The gas also

acquires other properties in virtue of its ionisation. Under

certain conditions it may acquire chemical activity and new

combinations may be formed or existing ones broken up. When its

initial velocity is expended the helium atom gives up its

properties as an alpha ray and thenceforth remains possessed of

the ordinary varying velocity of thermal agitation. Bragg and

Kleeman and others have investigated the career of the alpha ray

when its path or range lies in a gas at ordinary or obtainable

conditions of pressure and temperature. We will review some of

the facts ascertained.

The range or distance traversed in a gas at ordinary pressures is

a few centimetres. The following table, compiled by Geiger, gives

the range in air at the temperature of 15° C.:

cms.                   cms.                   cms.

Uranium 1 -   2.50    Thorium -     2.72     Radioactinium  4.60

Uranium 2 -   2.90    Radiothorium  3.87     Actinium X -   4.40

Ionium -      3.00    Thorium X -   4.30     Act Emanation  5.70

Radium -      3.30    Th Emanation  5.00     Actinium A -   6.50

Ra Emanation  4.16    Thorium A -   5.70     Actinium C -   5.40

Radium A -    4.75    Thorium C1 -  4.80

Radium C -    6.94    Thorium C2 -  8.60

Radium F -    3.77

It will be seen that the ray of greatest range is that proceeding

from thorium C2, which reaches a distance of 8.6 cms. In the

uranium family the fastest ray is

215

that of radium C. It attains 6.94 cms. There is thus an

appreciable difference between the ultimate distances traversed

by the most energetic rays of the two families. The shortest

ranges are those of uranium 1 and 2.

The ionisation effected by these rays is by no means uniform

along the path of the ray. By examining the conductivity of the

gas at different points along the path of the ray, the ionisation

at these points may be determined. At the limits of the range the

ionisation

{Fig. 13}

ceases. In this manner the range is, in fact, determined. The

dotted curve (Fig. 13) depicts the recent investigation of the

ionisation effected by a sheaf of parallel rays of radium C in

air, as determined by Geiger. The range is laid out horizontally

in centimetres. The numbers of ions are laid out vertically. The

remarkable nature of the results will be at once apparent. We

should have expected that the ray at the beginning of its path,

when its velocity and kinetic energy were greatest, would have

been more effective than towards the end of its range

216

when its energy had almost run out. But the curve shows that it

is just the other way. The lagging ray, about to resign its

ionising properties, becomes a much more efficient ioniser than

it was at first. The maximum efficiency is, however, in the case

of a bundle of parallel rays, not quite at the end of the range,

but about half a centimetre from it. The increase to the maximum

is rapid, the fall from the maximum to nothing is much more

rapid.

It can be shown that the ionisation effected anywhere along the

path of the ray is inversely proportional to the velocity of the

ray at that point. But this evidently does not apply to the last

5 or 10 mms. of the range where the rate of ionisation and of the

speed of the ray change most rapidly. To what are the changing

properties of the rays near the end of their path to be ascribed?

It is only recently that this matter has been elucidated.

When the alpha ray has sufficiently slowed down, its power of

passing right through atoms, without appreciably experiencing any

effects from them, diminishes. The opposing atoms begin to exert

an influence on the path of the ray, deflecting it a little. The

heavier atoms will deflect it most. This effect has been very

successfully investigated by Geiger. It is known as "scattering."

The angle of scattering increases rapidly with the decrease of

velocity. Now the effect of the scattering will be to cause some

of the rays to complete their ranges

217

or, more accurately, to leave their direct line of advance a

little sooner than others. In the beautiful experiments of C. T.

R. Wilson we are enabled to obtain ocular demonstration of the

scattering. The photograph (Fig. 14.), which I owe to the

kindness of Mr. Wilson, shows the deflection of the ray towards

the end of its path. In

{Fig. 14}

this case the path of the ray has been rendered visible by the

condensation of water particles under the influence of the

ionisation; the atmosphere in which the ray travels being in a

state of supersaturation with water vapour at the instant of the

passage of the ray. It is evident that if we were observing the

ionisation along a sheaf of parallel rays, all starting with

equal velocity,

218

the effect of the bending of some of the rays near the end of

their range must be to cause a decrease in the aggregate

ionisation near the very end of the ultimate range. For, in fact,

some of the rays complete their work of ionising at points in the

gas before the end is reached. This is the cause, or at least an

important contributory cause, of the decline in the ionisation

near the end of the range, when the effects of a bundle of rays

are being observed. The explanation does not suggest that the

ionising power of any one ray is actually diminished before it

finally ceases to be an alpha ray.

The full line in Fig. 13 gives the ionisation curve which it may

be expected would be struck out by a single alpha ray. In it the

ionisation goes on increasing till it abruptly ceases altogether,

with the entire loss of the initial kinetic energy of the

particle.

A highly remarkable fact was found out by Bragg. The effect of

the atom traversed by the ray in checking the velocity of the ray

is independent of the physical and chemical condition of the

atom. He measured the "stopping power" of a medium by the

distance the ray can penetrate into it compared with the distance

to which it can penetrate in air. The less the ratio the greater

is the stopping power. The stopping power of a substance is

proportional to the square root of its atomic weight. The

stopping power of an atom is not altered if it is in chemical

union with another atom. The atomic weight is the one quality of

importance. The physical

219

state, whether the element is in the solid, liquid or gaseous

state, is unimportant. And when we deal with molecules the

stopping power is simply proportional to the sum of the square

roots of the atomic weights of the atoms entering into the

molecule. This is the "additive law," and it obviously enables us

to calculate what the range in any substance of known chemical

composition and density will be, compared with the range in air.

This is of special importance in connection with phenomena we

have presently to consider. It means that, knowing the chemical

composition and density of any medium whatsoever, solid, liquid

or gaseous, we can calculate accurately the distance to which any

particular alpha ray will penetrate. Nor have the temperature and

pressure to which the medium is subjected any influence save in

so far as they may affect the proximity of one atom to another.

The retardation of the alpha ray in the atom is not affected.

This valuable additive law, however, cannot be applied in

strictness to the amount of ionisation attending the ray. The

form of the molecule, or more generally its volume, may have an

influence upon this. Bragg draws the conclusion, from this fact

as well as from the notable increase of ionisation with loss of

speed, that the ionisation is dependent upon the time the ray

spends in the molecule. The energy of the ray is, indeed, found

to be less efficient in producing ionisation in the smaller

atomm.

220

Before leaving our review of the general laws governing the

passage of alpha rays through matter, another point of interest

must be referred to. We have hitherto spoken in general terms of

the fact that ionisation attends the passage of the ray. We have

said nothing as to the nature of the ionisation so produced. But

in point of fact the ionisation due to an alpha ray is sui

generis. A glance at one of Wilson's photographs (Fig. 14.)

illustrates this. The white streak of water particles marks the

path of the ray. The ions produced are evidently closely crowded

along the track of the ray. They have been called into existence

in a very minute instant of time. Now we know that ions of

opposite sign if left to themselves recombine. The rate of

recombination depends upon the product of the number of each sign

present in unit volume. Here the numbers are very great and the

volume very small. The ionic density is therefore high, and

recombination very rapidly removes the ions after they are

formed. We see here a peculiarity of the ionisation effected by

alpha rays. It is linear in distribution and very local. Much of

the ionisation in gases is again undone by recombination before

diffusion leads to the separation of the ions. This "initial

recombination" is greatest towards the end of the path of the ray

where the ionisation is a maximum. Here it may be so effective

that the form of the curve is completely lost unless a very large

electromotive force is used to separate the ions when the

ionisation is being investigated.

221

We have now reviewed recent work at sufficient length to

understand something of the nature of the most important advance

ever made in our knowledge of the atom. Let us glance briefly at

what we have learned. The radioactive atom in sinking to a lower

atomic weight casts out with enormous velocity an atom of helium.

It thus loses a definite portion of its mass and of its energy.

Helium which is chemically one of the most inert of the elements,

is, when possessed of such great kinetic energy, able to

penetrate and ionise the atoms which it meets in its path. It

spends its energy in the act of ionising them, coming to rest,

when it moves in air, in a few centimetres. Its initial velocity

depends upon the particular radioactive element which has given

rise to it. The length of its path is therefore different

according to the radioactive element from which it proceeds. The

retardation which it experiences in its path depends entirely

upon the atomic weight of the atoms which it traverses. As it

advances in its path its effectiveness in ionising the atom

rapidly increases and attains a very marked maximum. In a gas the

ions produced being much crowded together recombine rapidly; so

rapidly that the actual ionisation may be quite concealed unless

a sufficiently strong electric force is applied to separate them.

Such is a brief summary of the climax of radioactive

discovery:—the birth, life and death of the alpha ray. Its advent

into Science has altered fundamentally our conception of

222

matter. It is fraught with momentous bearings upon Geological

Science. How the work of the alpha ray is sometimes recorded

visibly in the rocks and what we may learn from that record, I

propose now to bring before you.

In certain minerals, notably the brown variety of mica known as

biotite, the microscope reveals minute circular marks occurring

here and there, quite irregularly. The most usual appearance is

that of a circular area darker in colour than the surrounding

mineral. The radii of these little disc-shaped marks when well

defined are found to be remarkably uniform, in some cases four

hundredths of a millimetre and in others three hundredths, about.

These are the measurements in biotite. In other minerals the

measurements are not quite the same as in biotite. Such minute

objects are quite invisible to the naked eye. In some rocks they

are very abundant, indeed they may be crowded together in such

numbers as to darken the colour of the mineral containing them.

They have long been a mystery to petrologists.

Close examination shows that there is always a small speck of a

foreign body at the centre of the circle, and it is often

possible to identify the nature of this central substance, small

though it be. Most generally it is found to be the mineral

zircon. Now this mineral was shown by Strutt to contain radium in

quantities much exceeding those found in ordinary rock

substances.

223

Some other mineral may occasionally form the nucleus, but we

never find any which is not known to be specially likely to

contain a radioactive substance. Another circumstance we notice.

The smaller this central nucleus the more perfect in form is the

darkened circular area surrounding it. When the circle is very

perfect and the central mineral clearly defined at its centre we

find by measurement that the radius of the darkened area is

generally 0.033 mm. It may sometimes be 0.040 mm. These are

always the measurements in biotite. In other minerals the radii

are a little different.

We see in the photograph (Pl. XXIII, lower figure), much

magnified, a halo contained in biotite. We are looking at a

region in a rock-section, the rock being ground down to such a

thickness that light freely passes through it. The biotite is in

the centre of the field. Quartz and felspar surround it. The rock

is a granite. The biotite is not all one crystal. Two crystals,

mutually inclined, are cut across. The halo extends across both

crystals, but owing to the fact that polarised light is used in

taking the photograph it appears darker in one crystal than in

the other. We see the zircon which composes the nucleus. The fine

striated appearance of the biotite is due to the cleavage of that

mineral, which is cut across in the section.

The question arises whether the darkened area surrounding the

zircon may not be due to the influence of the radioactive

substances contained in the zircon. The

224

extraordinary uniformity of the radial measurements of perfectly

formed haloes (to use the name by which they have long been

known) suggests that they may be the result of alpha radiation.

For in that case, as we have seen, we can at once account for the

definite radius as simply representing the range of the ray in

biotite. The furthest-reaching ray will define the radius of the

halo. In the case of the uranium family this will be radium C,

and in the case of thorium it will be thorium C. Now here we

possess a means of at once confirming or rejecting the view that

the halo is a radioactive phenomenon and occasioned by alpha

radiation; for we can calculate what the range of these rays will

be in biotite, availing ourselves of Bragg's additive law,

already referred to. When we make this calculation we find that

radium C just penetrates 0.033 mm. and thorium C 0.040 mm. The

proof is complete that we are dealing with the effects of alpha

rays. Observe now that not only is the coincidence of measurement

and calculation a proof of the view that alpha radiation has

occasioned the halo, but it is a very complete verification of

the important fact stated by Bragg, that the stopping power

depends solely on the atomic weight of the atoms traversed by the

ray.

We have seen that our examination of the rocks reveals only the

two sorts of halo: the radium halo and the thorium halo. This is

not without teaching. For why not find an actinium halo? Now

Rutherford long ago suggested that this element and its

derivatives were

225

probably an offspring of the uranium family; a side branch, as it

were, in the formation of which relatively few transforming atoms

took part. On Rutherford's theory then, actinium should always

accompany uranium and radium, but in very subordinate amount. The

absence of actinium haloes clearly supports this view. For if

actinium was an independent element we would be sure to find

actinium haloes. The difference in radius should be noticeable.

If, on the other hand, actinium

was always associated with uranium and radium, then its effects

would be submerged in those of the much more potent effects of

the uranium series of elements.

It will have occurred to you already that if the radioactive

origin of the halo is assured the shape of a halo is not really

circular, but spherical. This is so. There is no such thing as a

disc-shaped halo. The halo is a spherical volume containing the

radioactive nucleus at its centre. The true radius of the halo

may, therefore, only be measured on sections passing through the

nucleus.

226

In order to understand the mode of formation of a halo we may

profitably study on a diagram the events which go on within the

halo-sphere. Such a diagram is seen in Fig. 15. It shows to

relatively correct scale the limiting range of all the alpha-ray

producing members of the uranium and thorium families. We know

that each member of a family will exist in equilibrium amount

within the nucleus possessing the parent element. Each alpha ray

leaving the nucleus will just attain its range and then cease to

affect the mica. Within the halosphere, there must be, therefore,

the accumulated effects of the influences of all the rays. Each

has its own sphere of influence, and the spheres are all

concentric.

The radii in biotite of the several spheres are given in the

following table

URANIUM FAMILY.

Radium C -       0.0330 mm.

Radium A -       0.0224 mm.

Ra Emanation -   0.0196 mm.

Radium F -       0.0177 mm.

Radium -         0.0156 mm.

Ionium -         0.0141 mm.

Uranium 1 -      0.0137 mm.

Uranium 2 -      0.0118 mm.

THORIUM FAMILY.

Thorium CE -     0.040 mm.

Thorium A -      0.026 mm.

Th Emanation -   0.023 mm.

Thorium Ci -     0.022 mm.

Thorium X -      0.020 mm.

Radiothorium -   0.119 mm.

Thorium -        0.013 mm.

In the photograph (Pl. XXIV, lower figure), we see a uranium and

a thorium halo in the same crystal of mica. The mica is contained

in a rock-section and is cut across the cleavage. The effects of

thorium Ca are clearly shown

227

as a lighter border surrounding the accumulated inner darkening

due to the other thorium rays. The uranium halo (to the right)

similarly shows the effects of radium C, but less distinctly.

Haloes which are uniformly dark all over as described above are,

in point of fact, "over-exposed"; to borrow a familiar

photographic term. Haloes are found which show much beautiful

internal detail. Too vigorous action obscures this detail just as

detail is lost in an over-exposed photograph. We may again have

"under-exposed" haloes in which the action of the several rays is

incomplete or in which the action of certain of the rays has left

little if any trace. Beginning at the most under-exposed haloes

we find circular dark marks having the radius 0.012 or 0.013 mm.

These haloes are due to uranium, although their inner darkening

is doubtless aided by the passage of rays which were too few to

extend the darkening beyond the vigorous effects of the two

uranium rays. Then we find haloes carried out to the radii 0.016,

0.018 and 0.019 mm. The last sometimes show very beautiful outer

rings having radial dimensions such as would be produced by

radium A and radium C. Finally we may have haloes in which

interior detail is lost so far out as the radius due to emanation

or radium A, while outside this floats the ring due to radium C.

Certain variations of these effects may occur, marking,

apparently, different stages of exposure. Plates XXIII and XXIV

(upper figure) illustrate some of these stages;

228

the latter photograph being greatly enlarged to show clearly the

halo-sphere of radium A.

In most of the cases mentioned above the structure evidently

shows the existence of concentric spherical shells of darkened

biotite. This is a very interesting fact. For it proves that in

the mineral the alpha ray gives rise to the same increased

ionisation towards the end of its range, as Bragg determined in

the case of gases. And we must conclude that the halo in every

case grows in this manner. A spherical shell of darkened biotite

is first produced and the inner colouration is only effected as

the more feeble ionisation along the track of the ray in course

of ages gives rise to sufficient alteration of the mineral. This

more feeble ionisation is, near the nucleus, enhanced in its

effects by the fact that there all the rays combine to increase

the ionisation and, moreover, the several tracks are there

crowded by the convergency to the centre. Hence the most

elementary haloes seldom show definite rings due to uranium,

etc., but appear as embryonic disc-like markings. The photographs

illustrate many of the phases of halo development.

Rutherford succeeded in making a halo artificially by compressing

into a capillary glass tube a quantity of the emanation of

radium. As the emanation decayed the various derived products

came into existence and all the several alpha rays penetrated the

glass, darkening the walls of the capillary out to the limit of

the range of radium C in glass. Plate XXV shows a magnified

section of the

229

tube. The dark central part is the capillary. The tubular halo

surrounds it. This experiment has, however, been anticipated by

some scores of millions of years, for here is the same effect in

a biotite crystal (Pl. XXV). Along what are apparently tubular

passages or cracks in the mica, a solution, rich in radioactive

substances, has moved; probably during the final consolidation of

the granite in which the mica occurs. A continuous and very

regular halo has developed along these conduits. A string of

halo-spheres may lie along such passages. We must infer that

solutions or gases able to establish the radioactive nuclei moved

along these conduits, and we are entitled to ask if all the

haloes in this biotite are not, in this sense, of secondary

origin. There is, I may add, much to support such a conclusion.

The widespread distribution of radioactive substances is most

readily appreciated by examination of sections of rocks cut thin

enough for microscopic investigation. It is, indeed, difficult to

find, in the older rocks of granitic type, mica which does not

show haloes, or traces of haloes. Often we find that every one of

the inclusions in the mica—that is, every one of the earlier

formed substances—contain radioactive elements, as indicated by

the presence of darkened borders. As will be seen presently the

quantities involved are generally vanishingly small. For example

it was found by direct determination that in one gram of the

halo-rich mica of Co. Carlow there was rather less than twelve

billionths of a gram of radium, We are

230

entitled to infer that other rare elements are similarly widely

distributed but remain undetectable because of their more stable

properties.

It must not be thought that the under-exposed halo is a recent

creation. By no means. All are old, appallingly old; and in the

same rock all are, probably, of the same, or neatly the same,

age. The under-exposure is simply due to a lesser quantity of the

radioactive elements in the nucleus. They are under-exposed, in

short, not because of lesser duration of exposure, but because of

insufficient action; as when in taking a photograph the stop is

not open enough for the time of the exposure.

The halo has, so far, told us that the additive law is obeyed in

solid media, and that the increased ionisation attending the

slowing down of the ray obtaining in gases, also obtains in

solids; for, otherwise, the halo would not commence its

development as a spherical shell or envelope. But here we learn

that there is probably a certain difference in the course of

events attending the immediate passage of the ray in the gas and

in the solid. In the former, initial recombination may obscure

the intense ionisation near the end of the range. We can only

detect the true end-effects by artificially separating the ions

by a strong electric force. If this recombination happened in the

mineral we should not have the concentric spheres so well defined

as we see them to be. What, then, hinders the initial

recombination in the solid? The answer probably is that the newly

formed

231

ion is instantly used up in a fresh chemical combination. Nor is

it free to change its place as in the gas. There is simply a new

equilibrium brought about by its sudden production. In this

manner the conditions in the complex molecule of biotite,

tourmaline, etc., may be quite as effective in preventing initial

recombination as the most effective electric force we could

apply. The final result is that we find the Bragg curve

reproduced most accurately in the delicate shading of the rings

making up the perfectly exposed halo.

That the shading of the rings reproduces the form of the Bragg

curve, projected, as it were, upon the line of advance of the ray

and reproduced in depth of shading, shows that in yet another

particular the alpha ray behaves much the same in the solid as in

the gas. A careful examination of the outer edge of the circles

always reveals a steep but not abrupt cessation of the action of

the ray. Now Geiger has investigated and proved the existence of

scattering of the alpha ray by solids. We may, therefore, suppose

with much probability that there is the same scattering within

the mineral near the end of the range. The heavy iron atom of the

biotite is, doubtless, chiefly responsible for this in biotite

haloes. I may observe that this shading of the outer bounding

surface of the sphere of action is found however minute the

central nucleus. In the case of a nucleus of considerable size

another effect comes in which tends to produce an enhanced

shading. This will

232

result if rays proceed from different depths in the nucleus. If

the nucleus were of the same density and atomic weight as the

surrounding mica, there would be little effect. But its density

and molecular weight are generally greater, hence the retardation

is greater, and rays proceeding from deep in the nucleus

experience more retardation than those which proceed from points

near to the surface. The distances reached by the rays in the

mica will vary accordingly, and so there will be a gradual

cessation of the effects of the rays.

The result of our study of the halo may be summed up in the

statement that in nearly every particular we have the phenomena,

which have been measured and observed in the gas, reproduced on a

minute scale in the halo. Initial recombination seems, however,

to be absent or diminished in effectiveness; probably because of

the new stability instantly assumed by the ionised atoms.

One of the most interesting points about the halo remains to be

referred to. The halo is always uniformly darkened all round its

circumference and is perfectly spherical. Sections, whether taken

in the plane of cleavage of the mica or across it, show the same

exactly circular form, and the same radius. Of course, if there

was any appreciable increase of range along or across the

cleavage the form of the halo on the section across the cleavage

should be elliptical. The fact that there is no measurable

ellipticity is, I think, one which on first consideration would

not be expected.

233

For what are the conditions attending the passage of the ray in a

medium such as mica? According to crystallographic conceptions we

have here an orderly arrangement of molecules, the units

composing the crystal being alike in mass, geometrically spaced,

and polarised as regards the attractions they exert one upon

another. Mica, more especially, has the cleavage phenomenon

developed to a degree which transcends its development in any

other known substance. We can cleave it and again cleave it till

its flakes float in the air, and we may yet go on cleaving it by

special means till the flakes no longer reflect visible light.

And not less remarkable is the uniplanar nature of its cleavage.

There is little cleavage in any plane but the one, although it is

easy to show that the molecules in the plane of the flake are in

orderly arrangement and are more easily parted in some directions

than in others. In such a medium beyond all others we must look

with surprise upon the perfect sphere struck out by the alpha

rays, because it seems certain that the cleavage is due to lesser

attraction, and, probably, further spacing of the molecules, in a

direction perpendicular to the cleavage.

It may turn out that the spacing of the molecules will influence

but little the average number per unit distance encountered by

rays moving in divergent paths. If this is so, we seem left to

conclude that, in spite of its unequal and polarised attractions,

there is equal retardation and equal ionisation in the molecule

in whatever

234

direction it is approached. Or, again, if the encounters indeed

differ in number, then some compensating effect must exist

whereby a direction of lesser linear density involves greater

stopping power in the molecule encountered, and vice versa.

The nature of the change produced by the alpha rays is unknown.

But the formation of the halo is not, at least in its earlier

stages, attended by destruction of the crystallographic and

optical properties of the medium. The optical properties are

unaltered in nature but are increased in intensity. This applies

till the halo has become so darkened that light is no longer

transmitted under the conditions of thickness obtaining in rock

sections. It is well known that there is in biotite a maximum

absorption of a plane-polarised light ray, when the plane of

vibration coincides with the plane of cleavage. A section across

the cleavage then shows a maximum amount of absorption. A halo

seen on this section simply produces this effect in a more

intense degree. This is well shown in Plate XXIII (lower figure),

on a portion of the halo-sphere. The descriptive name "Pleochroic

Halo" has originated from this fact. We must conclude that the

effect of the ionisation due to the alpha ray has not been to

alter fundamentally the conditions which give rise to the optical

properties of the medium. The increased absorption is probably

associated with some change in the chemical state of the iron

present. Haloes are, I believe, not found in minerals from which

this

235

element is absent. One thing is quite certain. The colouration is

not due to an accumulation of helium atoms, _i.e._ of spent alpha

rays. The evidence for this is conclusive. If helium was

responsible we should have haloes produced in all sorts of

colourless minerals. Now we sometimes see zircons in felspars and

in quartz, etc., but in no such case is a halo produced. And

halo-spheres formed within and sufficiently close to the edge of

a crystal of mica are abruptly truncated by neighbouring areas of

fclspar or quartz, although we know that the rays must pass

freely across the boundary. Again it is easy to show that even in

the oldest haloes the quantity of helium involved is so small

that one might say the halo-sphere was a tolerably good vacuum as

regards helium. There is, finally, no reason to suppose that the

imprisoned helium would exhibit such a colouration, or, indeed,

any at all.

I have already referred to the great age of the halo. Haloes are

not found in the younger igneous rocks. It is probable that a

halo less than a million years old has never been seen. This,

primâ facie, indicates an extremely slow rate of formation. And

our calculations quite support the conclusions that the growth of

a halo, if this has been uniform, proceeds at a rate of almost

unimaginable slowness.

Let us calculate the number of alpha rays which may have gone to

form a halo in the Devonian granite of Leinster.

236

It is common to find haloes developed perfectly in this granite,

and having a nucleus of zircon less than 5 x 10-4 cms. in

diameter. The volume of zircon is 65 x 10-12 c.cs. and the mass

3 x 10-10 grm.; and if there was in this zircon 10-8 grm. radium

per gram (a quantity about five times the greatest amount

measured by Strutt), the mass of radium involved is 3 x 10-18

grm. From this and from the fact ascertained by Rutherford that

the number of alpha rays expelled by a gram of radium in one

second is 3.4 x 10^10, we find that three rays are shot from the

nucleus in a year. If, now, geological time since the Devonian is

50 millions of years, then 150 millions of rays built up the

halo. If geological time since the Devonian is 400 millions of

years, then 1,200 millions of alpha rays are concerned in its

genesis. The number of ions involved, of course, greatly exceeds

these numbers. A single alpha ray fired from radium C will

produce 2.37 x 10^5 ions in air.

But haloes may be found quite clearly defined and fairly dark out

to the range of the emanation ray and derived from much less

quantities of radioactive materials. Thus a zircon nucleus with a

diameter of but 3.4 x 10-4 cms. formed a halo strongly darkened

within, and showing radium A and radium C as clear smoky rings.

Such a nucleus, on the assumption made above as to its radium

content, expels one ray in a year. But, again, haloes are

observed with less blackened pupils and with faint ring due to

radium C, formed round nuclei

237

of rather less than 2 x 10-4 cms. diameter. Such nuclei would

expel one ray in five years. And even lesser nuclei will generate

in these old rocks haloes with their earlier characteristic

features clearly developed. In the case of the most minute

nuclei, if my assumption as to the uranium content is correct, an

alpha ray is expelled, probably, no oftener than once in a

century; and possibly at still longer intervals.

The equilibrium amount of radium contained in some nuclei may

amount to only a few atoms. Even in the case of the larger nuclei

and more perfectly developed haloes the quantity of radium

involved is many millions of times less than the least amount we

can recognise by any other means. But the delicacy of the

observation is not adequately set forth in this statement. We can

not only tell the nature of the radioactive family with which we

are dealing; but we can recognise the presence of some of its

constituent members. I may say that it is not probable the

zircons are richer in radium than I have assumed. My assumption

involves about 3 per cent. of uranium. I know of no analyses

ascribing so great an amount of uranium to zircon. The variety

cyrtolite has been found to contain half this amount, about. But

even if we doubled our estimate of radium content, the remarkable

nature of our conclusions is hardly lessened.

It may appear strange that the ever-interesting question of the

Earth's age should find elucidation from the

238

study of haloes. Nevertheless the subjects are closely connected.

The circumstances are as follows. Geologists have estimated the

age of the Earth since denudation began, by measurements of the

integral effects of denudation. These methods agree in showing an

age of about rob years. On the other hand, measurements have been

made of the accumulation in minerals of radioactive _débris_—the

helium and lead—and results obtained which, although they do not

agree very well among themselves, are concordant in assigning a

very much greater age to the rocks. If the radioactive estimate

is correct, then we are now living in a time when the denudative

forces of the Earth are about eight or nine times as active as

they have been on the average over the past. Such a state of

things is absolutely unaccountable. And all the more

unaccountable because from all we know we would expect a somewhat

_lesser_ rate of solvent denudation as the world gets older and the

land gets more and more loaded with the washed-out materials of

the rocks.

Both the methods referred to of finding the age assume the

principle of uniformity. The geologist contends for uniformity

throughout the past physical history of the Earth. The physicist

claims the like for the change-rates of the radioactive elements.

Now the study of the rocks enables us to infer something as to

the past history of our Globe. Nothing is, on the other hand,

known respecting the origin of uranium or thorium—the parent

radioactive bodies. And while not questioning the law

239

and regularity which undoubtedly prevail in the periods of the

members of the radioactive families, it appears to me that it is

allowable to ask if the change rate of uranium has been always

what we now believe it to be. This comes to much the same thing

as supposing that atoms possessing a faster change rate once were

associated with it which were capable of yielding both helium and

lead to the rocks. Such atoms might have been collateral in

origin with uranium from some antecedent element. Like helium,

lead may be a derivative from more than one sequence of

radioactive changes. In the present state of our knowledge the

possibilities are many. The rate of change is known to be

connected with the range of the alpha ray expelled by the

transforming element; and the conformity of the halo with our

existing knowledge of the ranges is reason for assuming that,

whatever the origin of the more active associate of uranium, this

passed through similar elemental changes in the progress of its

disintegration. There may, however, have been differences in the

ranges which the halo would not reveal. It is remarkable that

uranium at the present time is apparently responsible for two

alpha rays of very different ranges. If these proceed from

different elements, one should be faster in its change rate than

the other. Some guidance may yet be forthcoming from the study of

the more obscure problems of radioactivity.

Now it is not improbable that the halo may contribute directly to

this discussion. We can evidently attack

240

the biotite with a known number of alpha rays and determine how

many are required to produce a certain intensity of darkening,

corresponding to that of a halo with a nucleus of measurable

dimensions. On certain assumptions, which are correct within

defined limits, we can calculate, as I have done above, the

number of rays concerned in forming the halo. In doing so we

assume some value for the age of the halo. Let us take the

maximum radioactive value. A halo originating in Devonian times

may attain a certain central blackening from the effects of, say,

rob rays. But now suppose we find that we cannot produce the same

degree of blackening with this number of rays applied in the

laboratory. What are we to conclude? I think there is only the

one conclusion open to us; that some other source of alpha rays,

or a faster rate of supply, existed in the past. And this

conclusion would explain the absence of haloes from the younger

rocks; which, in view of the vast range of effects possible in

the development of haloes, is, otherwise, not easy to account

for. It is apparent that the experiment on the biotite has a

direct bearing on the validity of the radioactive method of

estimating the age of the rocks. It is now being carried out by

Professor Rutherford under reliable conditions.

Finally, there is one very certain and valuable fact to be

learned from the halo. The halo has established the extreme

rarity of radioactivity as an atomic phenomenon. One and all of

the speculations as to

241

the slow breakdown of the commoner elements may be dismissed. The

halo shows that the mica of the rocks is radioactively sensitive.

The fundamental criterion of radioactive change is the expulsion

of the alpha ray. The molecular system of the mica and of many

other minerals is unstable in presence of these rays, just as a

photographic plate is unstable in presence of light. Moreover,

the mineral integrates the radioactive effects in the same way as

a photographic salt integrates the effects of light. In both

cases the feeblest activities become ultimately apparent to our

inspection. We have seen that one ray in each year since the

Devonian period will build the fully formed halo: an object

unlike any other appearance in the rocks. And we have been able

to allocate all the haloes so far investigated to one or the

other of the known radioactive families. We are evidently

justified in the belief that had other elements been radioactive

we must either find characteristic haloes produced by them, or

else find a complete darkening of the mica. The feeblest alpha

rays emitted by the relatively enormous quantities of the

prevailing elements, acting over the whole duration of geological

time—and it must be remembered that the haloes we have been

studying are comparatively young—must have registered their

effects on the sensitive minerals. And thus we are safe in

concluding that the common elements, and, indeed, many which

would be called rare, are possessed of a degree of stability

which has preserved them un

242

changed since the beginning of geological time. Each unaffected

flake of mica is, thus, unassailable proof of a fact which but

for the halo would, probably, have been for ever beyond our

cognisance.

THE USE OF RADIUM IN MEDICINE [1]

IT has been unfortunate for the progress of the radioactive

treatment of disease that its methods and claims involve much of

the marvellous. Up till recently, indeed, a large part of

radioactive therapeutics could only be described as bordering on

the occult. It is not surprising that when, in addition to its

occult and marvellous characters, claims were made on its behalf

which in many cases could not be supported, many medical men came

to regard it with a certain amount of suspicion.

Today, I believe, we are in a better position. I think it is

possible to ascribe a rational scientific basis to its legitimate

claims, and to show, in fact, that in radioactive treatment we

are pursuing methods which have been already tried extensively

and found to be of definite value; and that new methods differ

from the old mainly in their power and availability, and little,

or not at all, in kind.

Let us briefly review the basis of the science. Radium is a

metallic element chemically resembling barium. It

[1] A Lecture to Postgraduate Students of Medicine in connection

with the founding of the Dublin Radium Institute, delivered in

the School of Physic in Ireland, Trinity College, on October 2nd,

1914

244

possesses, however, a remarkable property which barium does not.

Its atoms are not equally stable. In a given quantity of radium a

certain very small percentage of the total number of atoms

present break up per second. By "breaking up" we mean their

transmutation to another element. Radium, which is a solid

element under ordinary conditions, gives rise by transmutation to

a gaseous element—the emanation of radium. The new element is a

heavy gas at ordinary temperatures and, like other gases, can be

liquified by extreme cold. The extraordinary property of

transmutation is entirely automatic. No influence which chemist

or physicist can apply can affect the rate of transformation.

The emanation inherits the property of instability, but in its

case the instability is more pronounced. A relatively large

fraction of its atoms transmute per second to a solid element

designated Radium A. In turn this new generation of atoms breaks

up—even faster than the emanation—becoming yet another element

with specific chemical properties. And so on for a whole sequence

of transmutations, till finally a stable substance is formed,

identical with ordinary lead in chemical and physical properties,

but possessing a slightly lower atomic weight.

The genealogy of the radium series of elements shows that radium

is not the starting point. It possesses ancestors which have been

traced back to the element uranium.

Now what bearing has this series of transmutations

245

upon medical science? Radium or emanation, &c., are not in the

Pharmacopoeia as are, say, arsenic or bismuth. The whole

medicinal value of these elements resides in the very wonderful

phenomena of their radiations. They radiate in the process of

transmuting.

The changing atom may radiate a part of its own mass. The

"alpha"-ray (a-ray) is such a material ray. It is an electrified

helium atom cast out of the parent atom with enormous

velocity—such a velocity as would carry it, if not impeded, all

round the earth in two seconds. All alpha-rays are positively

electrified atoms of the element helium, which thereby is shown

to be an integral constituent of many elements. The alpha-ray is

not of much value to medical science, for, in spite of its great

velocity, it is soon stopped by encounter with other atoms. It

can penetrate only a minute fraction of a millimetre into

ordinary soft tissues. We shall not further consider it.

Transmuting atoms give out also material rays of another kind:

the ß-rays. The ß-ray is in mass but a very small fraction of,

even, a hydrogen atom. Its speed may approach that of light. As

cast out by radioactive elements it starts with speeds which vary

with the element, and may be from one-third to nine-tenths the

velocity of light. The ß-ray is negatively electrified. It has

long been known to science as the electron. It is also identical

with the cathode ray of the vacuum tube.

246

Another and quite different kind of radiation is given out by

many of the transmuting elements:—the y-ray. This is not

material, it is ethereal. It is known now with certainty that the

y-ray is in kind identical with light, but of very much shorter

wave length than even the extreme ultraviolet light of the solar

spectrum. The y-ray is flashed from the transmuting atom along

with the ß-ray. It is identical in character with the x-ray but

of even shorter wave length.

There is a very interesting connection between the y-ray and the

ß-ray which it is important for the medical man to understand—as

far as it is practicable on our present knowledge.

When y-rays or x-rays fall on matter they give rise to ß-rays.

The mechanism involved is not known but it is possibly a result

of the resonance of the atom, or of parts of it, to the short

light waves. And it is remarkable that the y-rays which, as we

have seen, are shorter and more penetrating waves than the

x-rays, give rise to ß-rays possessed of greater velocity and

penetration than ß-rays excited by the x-rays. Indeed the ß-rays

originated by y-rays may attain a velocity nearly approaching

that of light and as great as that of any ß-rays emitted by

transmuting atoms. Again there is demonstrable evidence that

ß-rays impinging on matter may give rise to y-rays. The most

remarkable demonstration of this is seen in the x-ray tube. Here

the x-rays originate where the stream of ß- or cathode-rays

247

are arrested on the anode. But the first relation is at present

of most importance to us—_i.e._ that the y-or x-rays give rise to

ß-rays.

This relation gives us additional evidence of the identity of the

physical effects of y-, x-, and light-rays —using the term light

rays in the usual sense of spectral rays. For it has long been

known that light waves liberate electrons from atoms. It has been

found that these electrons possess a certain initial velocity

which is the greater the shorter the wave length of the light

concerned in their liberation. The whole science of

"photo-electricity" centres round this phenomenon. The action of

light on the photographic plate, as well as many other physical

and chemical phenomena, find an explanation in this liberation of

the electron by the light wave.

Here, then, we have spectral light waves liberating

electrons—_i.e._ very minute negatively-charged particles, and we

find that, as we use shorter light waves, the initial velocity of

these particles increases. Again, we have x-rays which are far

smaller in wave length than spectral light, liberating much

faster negatively electrified particles. Finally, we have

y-rays—the shortest nether waves of all-liberating negative

particles of the highest velocity known. Plainly the whole series

of phenomena is continuous.

We can now look closer at the actions involved in the therapeutic

influence of the several rays and in

248

this way, also, see further the correlation between what may be

called photo-therapeutics and radioactive therapeutics.

The ß-ray, whether we obtain it directly from the transforming

radioactive atom or whether we obtain it as a result of the

effects of the y- or x-rays upon the atom, is an ionising agent

of wonderful power. What is meant by this? In its physical aspect

this means that the atoms through which it passes acquire free

electric charges; some becoming positive, some negative. This can

only be due to the loss of an electron by the affected atom. The

loss of the small negative charge carried in the electron leaves

the atom positively electrified or creates a positive ion. The

fixing of the wandering electron to a neutral atom creates a

negative ion. Before further consideration of the importance of

the phenomenon of ionisation we must fix in our minds that the

agent, which brings this about, is the ß-ray. There is little

evidence that the y-ray can directly create ions to any large

extent. But the action of liberating high-speed ß-rays results in

the creation of many thousands of ions by each ß-ray liberated.

As an agent in the hands of the medical man we must regard the

y-ray as a light wave of extremely penetrating character, which

creates high-speed ß-rays in the tissues which it penetrates,

these ß-rays being most potent ionising agents. The ß-rays

directly obtained from radioactive atoms assist in the work of

ionisation. ß-rays do not

249

penetrate far from their source. The fastest of them would not

probably penetrate one centimetre in soft tissues.

We must now return to the phenomenon of ionisation. Ionisation is

revealed to observation most conspicuously when it takes place in

a gas. The + and - electric charges on the gas particles endow it

with the properties of a conductor of electricity, the + ions

moving freely in one direction and the - ions in the opposite

direction under an electric potential. But there are effects

brought about by ionisation of more importance to the medical man

than this. The chemist has long come to recognise that in the ion

he is concerned with the inner mechanism of a large number of

chemical phenomena. For with the electrification of the atom

attractive and repulsive forces arise. We can directly show the

chemical effects of the ionising ß-rays. Water exposed to their

bombardment splits up into hydrogen and oxygen. And, again, the

separated atoms may be in part recombined under the influence of

the radiation. Ammonia splits up into hydrogen and nitrogen.

Carbon dioxide forms carbon, carbon monoxide, and oxygen;

hydrochloric acid forms chlorine and hydrogen. In these cases,

also, recombination can be partially effected by the rays.

We can be quite sure that within the complex structure of the

living cell the ionising effects which everywhere accompany the

ß-rays must exert a profound influence. The sequence of chemical

events which as yet seem

250

beyond the ken of science and which are involved in metabolism

cannot fail to be affected. Any, it is not surprising that as the

result of eaperinient it is found that the radiations are agents

which may be used either for the stimulation of the natural

events of growth or used for the actual destruction of the cell.

It is easy to see that the feeble radiation should produce the

one effect, the strong the other. In a similar way by a moderate

light stimulus we create the latent image in the photographic

plate; by an intense light we again destroy this image. The inner

mechanism in this last case can be logically stated.[1]

_There is plainly a true physical basis here for the efficacy of

radioactive treatment and, what is more, we find when we examine

it, that it is in kind not different from that underlying

treatment by spectral radiations. But in degree it is very

different and here is the reason for the special importance of

radioactivity as a therapeutic agent._ The Finsen light is capable

of influencing the soft tissues to a short depth only. The reason

is that the wave length of the light used is too great to pass

without rapid absorption through the tissues; and, further, the

electrons it gives rise to—_i.e._ the ß-rays it liberates—are too

slow-moving to be very efficient ionisers. X-rays penetrate in

some cases quite freely and give rise to much faster and more

powerful ß-rays

[1] See _The Latent Image_, p. 202.

251

than can the Finsen light. But far more penetrating than x-rays

are the y-rays emitted in certain of the radioactive changes.

These give rise to ß-rays having a velocity approximate to that

of light.

The y-rays are, therefore, very penetrating and powerfully

ionising light waves; light waves which are quite invisible to

the eye and can beam right through the tissues of the body. To

the mind's eye only are they visible. And a very wonderful

picture they make. We see the transmuting atom flashing out this

light for an inconceivably short instant as it throws off the

ß-ray. And "so far this little candle throws his beams" in the

complex system of the cells, so far atoms shaken by the rays send

out ß-rays; these in turn are hurled against other atomic

systems; fresh separations of electrons arise and new attractions

and repulsions spring up and the most important chemical changes

are brought about. Our mental picture can claim to be no more

than diagrammatic of the reality. Still we are here dealing with

recognised physical and chemical phenomena, and their description

as "occult" in the derogatory sense is certainly not

justifiable.

Having now briefly reviewed the nature of the rays arising in

radioactive substances and the rationale of their influence, we

must turn to more especially practical considerations.

The Table given opposite shows that radium itself is responsible

for a- and ß-rays only. It happens that

252

Period in whioh ½ element is transformed.

URANIUM 1 & 2 { a 6 } x 10^9 years.

URANIUM X { a ß } 24.6 days.

IONIUM { a 8 } x 104 years.

RADIUM { a ß } 2 x 10^2 years.

EMANATION { a } 8.85 days.

RADIUM A { a 8 } minutes.

RADIUM B { ß y } 26.7 minutes.

RADIUM C { a ß y } 13.5 minutes.

RADIUM D { ß } 15 years.

RADIUM E { ß y } 4.8 days.

RADIUM (Polonium) F { a } 140 days.

Table showing the successive generations of the elements of the

Uranium-radium family, the character of their radiations and

their longevity.

253

the ß-rays emitted by radium are very "soft"—_i.e._ slow and

easily absorbed. The a-ray is in no case available for more than

mere surface application. Hence we see that, contrary to what is

generally believed, radium itself is of little direct therapeutic

value. Nor is the next body in succession—the emanation, for it

gives only a-rays. In fact, to be brief, it is not till we come

to Radium B that ß-rays of a relatively high penetrative quality

are reached; and it is not till we come to Radium C that highly

penetrative y-rays are obtained.

It is around this element, Radium C, that the chief medical

importance of radioactive treatment by this family of radioactive

bodies centres. Not only are ß-rays of Radium C very penetrating,

but the y-rays are perhaps the most energetic rays of the, kind

known. Further in the list there is no very special medical

interest.

Now, how can we get a supply of this valuable element Radium C?

We can obtain it from radium itself. For even if radium has been

deprived of its emanation (which is easily done by heating it or

bringing it into solution) in a few weeks we get back the Radium

C. One thing here we must be clear about. With a given quantity

of Radium only a certain definitely limited amount of Radium C,

or of emanation, or any other of the derived bodies, will be

associated. Why is this? The answer is because the several

successive elements are themselves decaying —_i.e._ changing one

into the other. The atomic per-

254

centage of each, which decays in a second, is a fixed quantity

which we cannot alter. Now if we picture radium which has been

completely deprived of its emanation, again accumulating by

automatic transmutation a fresh store of this element, we have to

remember:— (i) That the rate of creation of emanation by the

radium is practically constant; and (2) that the absolute amount

of the emanation decaying per second increases as the stock of

emanation increases. Finally, when the amount of accumulated

emanation has increased to such an extent that the number of

emanation atoms transmuting per second becomes exactly equal to

the number being generated per second, the amount of emanation

present cannot increase. This is called the equilibrium amount.

If fifteen members are elected steadily each year into a

newly-founded society the number of members will increase for the

first few years; finally, when the losses by death of the members

equal about fifteen per annum the society can get no bigger. It

has attained the equilibrium number of members.

This applies to every one of the successive elements. It takes

twenty-one days for the equilibrium quantity of emanation to be

formed in radium which has been completely de-emanated; and it

takes 3.8 days for half the equilibrium amount to be formed.

Again, if we start with a stock of emanation it takes just three

hours for the equilibrium amount of Radium C to be formed.

255

We can evidently grow Radium C either from radium itself or from

the emanation of radium. If we use a tube of radium we have an

almost perfectly constant quantity of Radium C present, for as

fast as the Radium C and intervening elements decay the Radium,

which only diminishes very slowly in amount, makes up the loss.

But, if we start off with a tube of emanation, we do not possess

a constant supply of Radium C, because the emanation is decaying

fairly rapidly and there is no radium to make good its loss. In

3.8 days about one half the emanation is transmuted and the

Radium C decreases proportionately and, of course, with the

Radium C the valuable radiations also decrease. In another 3.8

days—that is in about a week from the start—the radioactive value

of the tube has fallen to one-fourth of its original value.

But in spite of the inconstant character of the emanation tube

there are many reasons for preferring its use to the use of the

radium tube. Chief of these is the fact that we can keep the

precious radium safely locked up in the laboratory and not

exposed to the thousand-and-one risks of the hospital. Then,

secondly, the emanation, being a gas, is very convenient for

subdivision into a large number of very small tubes according to

the dosage required.

In fact the volume of the emanation is exceedingly minute. The

amount of emanation in equilibrium with one gramme of radium is

called the curie, and with one

256

milligramme the millicurie. Now, the volume of the curie is only

a little more than one half a cubic millimetre. Hence in dealing

with emanation from twenty or forty milligrammes of radium we are

dealing with very small volumes.

How may the emanation be obtained? The process is an easy one in

skilled and practised hands. The salt of radium—generally the

bromide or chloride—is brought into acid solution. This causes

the emanation to be freely given off as fast as it is formed. At

intervals we pump it off with a mercury pump.

Let us see how many millicuries we will in future be able to turn

out in the week in our new Dublin Radium Institute.[1] We shall

have about 130 milligrammes of radium. In 3.8 days we get 65

millicuries from this—_i.e._ half the equilibrium amount of 130

millicuries. Hence in the week, we shall have about 130

millicuries.

This is not much. Many experts consider this little enough for

one tube. But here in Dublin we have been using the emanation in

a more economical and effective manner than is the usage

elsewhere; according to a method which has been worked out and

developed in our own Radium Institute. The economy is obtained by

the very simple expedient of minutely subdividing the' dose. The

system in vogue, generally, is to treat the tumour by inserting

into it one or two very active

[1] Then recently established by the Royal Dublin Society.

257

tubes, containing, perhaps, up to 200 millicuries, or even more,

per tube. Now these very heavily charged tubes give a radiation

so intense at points close to the tube, due to the greater

density of the rays near the tube, and, also, to the action of

the softer and more easily absorbable rays, that it has been

found necessary to stop these softer rays—both the y and ß—by

wrapping lead or platinum round the tube. In this lead or

platinum some thirty per cent. or more of the rays is absorbed

and, of course, wasted. But in the absence of the screen there is

extensive necrosis of the tissues near the tubes.

If, however, in place of one or two such tubes we use ten or

twenty, each containing one-tenth or one-twentieth of the dose,

we can avail ourselves of the softer rays around each tube with

benefit. Thus a wasteful loss is avoided. Moreover a more uniform

"illumination" of the tissues results, just as we can illuminate

a hall more uniformly by the use of many lesser centres of light

than by the use of one intense centre of radiation. Also we get

what is called "cross-radiation,"which is found to be beneficial.

The surgeon knows far better what he is doing by this method.

Thus it may be arranged for the effects to go on with approximate

uniformity throughout the tumour instead of varying rapidly

around a central point or—and this may be very important— the

effects may be readily concentrated locally.

Finally, not the least of the benefit arises in the easy

technique of this new method. The quantities of

258

emanation employed can fit in the finest capillary glass tubing

and the hairlike tubes can in turn be placed in fine exploring

needles. There is comparatively little inconvenience to the

patient in inserting these needles, and there is the most perfect

control of the dosage in the number and strength of these tubes

and the duration of exposure.[1]

The first Radium Institute in Ireland has already done good work

for the relief of human suffering. It will have, I hope, a great

future before it, for I venture, with diffidence, to hold the

opinion, that with increased study the applications and claims of

radioactive treatment will increase.

[1] For particulars of the new technique and of some of the work

already accomplished, see papers, by Dr. Walter C. Stevenson,

_British Medical Journal_, July 4th, 1914, and March 20th, 1915.

259

SKATING [1]

IT is now many years ago since, as a student, I was present at a

college lecture delivered by a certain learned professor on the

subject of friction. At this lecture a discussion arose out of a

question addressed to our teacher: "How is it we can skate on ice

and on no other substance?"

The answer came back without hesitation: "Because the ice is so

smooth."

It was at once objected: "But you can skate on ice which is not

smooth."

This put the professor in a difficulty. Obviously it is not on

account of the smoothness of the ice. A piece of polished plate

glass is far smoother than a surface of ice after the latter is

cut up by a day's skating. Nevertheless, on the scratched and

torn ice-surface skating is still quite possible; on the smooth

plate glass we know we could not skate.

Some little time after this discussion, the connection between

skating and a somewhat abstruse fact in physical science occurred

to me. As the fact itself is one which has played a part in the

geological history of the earth,

[1] A lecture delivered before the Royal Dublin Society in 1905.

260

and a part of no little importance, the subject of skating,

whereby it is perhaps best brought home to every one, is

deserving of our careful attention. Let not, then, the title of

this lecture mislead the reader as to the importance of its

subject matter.

Before going on to the explanation of the wonderful freedom of

the skater's movements, I wish to verify what I have inferred as

to the great difference in the slipperiness of glass and the

slipperiness of ice. Here is a slab of polished glass. I can

raise it to any angle I please so that at length this brass

weight of 250 grams just slips down when started with a slight

shove. The angle is, as you see, about 12½ degrees. I now

transfer the weight on to this large slab of ice which I first

rapidly dry with soft linen. Observe that the weight slips down

the surface of ice at a much lower angle. It is a very low angle

indeed: I read it as between 4 and 5 degrees. We see by this

experiment that there is a great difference between the

slipperiness of the two surfaces as measured by what is called

"the angle of friction." In this experiment, too, the glass

possesses by far the smoother surface although I have rubbed the

deeper rugosities out of the ice by smoothing it with a glass

surface. Notwithstanding this, its surface is spotted with small

cavities due to bubbles and imperfections. It is certain that if

the glass was equally rough, its angle of friction towards the

brass weight would be higher.

261

We have, however, another comparative experiment to carry out. I

made as you saw a determination of the angle at which this weight

of 250 grams just slipped on the ice. The lower surface of the

weight, the part which presses on the ice, consists of a light,

brass curtain ring. This can be detached. Its mass is only 6½

grams, the curtain ring being, in fact, hollow and made of very

thin metal. We have, therefore, in it a very small weight which

presents exactly the same surface beneath as did the weight of

250 grams. You see, now, that this light weight will not slip on

ice at 5 or 6 degrees of slope, but first does so at about io

degrees.

This is a very important experiment as regards our present

inquiry. Ice appears to possess more than one angle of friction

according as a heavy or a light weight is used to press upon it.

We will make the same experiment with the plate of glass. You see

that there is little or no difference in the angle of friction of

brass on glass when we press the surfaces together with a heavy

or with a light weight. The light weight requires the same slope

of 12½ degrees to make it slip.

This last result is in accordance with the laws of friction. We

say that when solid presses on solid, for each pair of substances

pressed together there is a constant ratio between the force

required to keep one in motion over the other, and the force

pressing the solids together. This ratio is called"the

coefficient of friction."The coefficient is, in fact, constant or

approximately

262

so. I can determine the coefficient of friction from the angle of

friction by taking the tangent of the angle. The tangent of the

angle of friction is the coefficient of friction. If, then, the

coefficient is constant, so, of course, must the angle of

friction be constant. We have seen that it is so in the case of

metal on glass, but not so in the case of metal on ice. This

curious result shows that there is something abnormal about the

slipperiness of ice.

The experiments we have hitherto made are open to the reproach

that the surface of the ice is probably damp owing to the warmth

of the air in contact with it. I have here a means of dealing

with a surface of cold, dry ice. This shallow copper tank about

18 inches (45 cms.) long, and 4 inches (10 cms.) wide, is filled

with a freezing 'mixture circulated through it from a larger

vessel containing ice melting in hydrochloric acid at a

temperature of about -18° C. This keeps the tank below the

melting point of ice. The upper surface of the tank is provided

with raised edges so that it can be flooded with water. The water

is now frozen and its temperature is below 0° C. It is about

10° C. I can place over the ice a roof-shaped cover made of two

inclined slabs of thick plate glass. This acts to keep out warm

air, and to do away with any possibility of the surface of the

ice being wet with water thawed from the ice. The whole tank

along with its roof of glass can be adjusted to any angle, and a,

scale at the

263

raised end of the tank gives the angle of slope in degrees. A

weight placed on the ice can be easily seen through the glass

cover.

The weight we shall use consists of a very light ring of

aluminium wire which is rendered plainly visible by a ping-pong

ball attached above it. The weight rests now on a copper plate

provided for the purpose at the upper end of the tank. The plate

being in direct contact beneath with the freezing mixture we are

sure that the aluminium ring is no hotter than the ice. A light

jerk suffices to shake the weight on to the surface of the ice.

We find that this ring loaded with only the ping-pong ball, and

weighing a total of 2.55 grams does not slip at the low angles. I

have the surface of the ice at an angle of rather over 13½, and

only by continuous tapping of the apparatus can it be induced to

slip down. This is a coefficient of 0.24, and compares with the

coefficient of hard and smooth solids on one another. I now

replace the empty ping-pong ball by a similar ball filled with

lead shot. The total weight is now 155 grams. You see the angle

of slipping has fallen to 7°.

Every one who has made friction experiments knows how

unsatisfactory and inconsistent they often are. We can only

discuss notable quantities and broad results, unless the most

conscientious care be taken to eliminate errors. The net result

here is that ice at about -10° C. when pressed on by a very light

weight possesses a

264

coefficient of friction comparable with the usual coefficients of

solids on solids, but when the pressure is increased, the

coefficient falls to about half this value.

The following table embodies some results obtained on the

friction of ice and glass, using the methods I have shown you. I

add some of the more carefully determined coefficients of other

observers.

Wt. in      On Plate         On Ice         On Ice

Grams.      Glass.           at 0° C.       at 10° C.

Angle. Coeff.    Angle. Coeff.  Angle. Coeff

Aluminium   2.55    12½°  0.22        12°   0.21     13½°   0.24

Same      155       12½°   0.22        6°   0.11       7°   0.12

Brass       6.5     12½°  0.22        10°   0.17     10½°   0.18

Same      107       12½°   0.22        5°   0.09       6°   0.10

Steel on steel (Morin) - - - - 0.14

Brass on cast iron (Morin) - - 0.19

Steel on cast iron (Morin) - - 0.20

Skate on ice (J. Müller) - - - 0.016—0.032

Best-greased surfaces (Perry) - 0.03—0.036

You perceive from the table that while the friction of brass or

aluminium on glass is quite independent of the weight used, that

of brass or aluminium on ice depends in some way upon the weight,

and falls in a very marked degree when the weight is heavy. Now,

I think that if we had been on the look out for any abnormality

in the friction of hard substances on ice, we would have rather

anticipated a variation in the

265

other direction. We would have, perhaps, expected that a heavy

weight would have given rise to the greater friction. I now turn

to the explanation of this extraordinary result.

You are aware that it requires an expenditure of heat merely to

convert ice to water, the water produced being at the temperature

of the ice, _i.e._ at 0° C., from which it is derived. The heat

required to change the ice from the solid to the liquid state is

the latent heat of water. We take the unit quantity of heat to be

that which is required to heat 1 kilogram of water 1° C. Then if

we melt 1 kilogram of ice, we must supply it with 80 such units

of heat. While melting is going on, there is no change of

temperature if the experiment is carefully conducted. The melting

ice and the water coming from it remain at 0° C. throughout the

operation, and neither the thermometer nor your own sensations

would tell you of the amount of heat which was flowing in. The

heat is latent or hidden in the liquid produced, and has gone to

do molecular work in the substance. Observe that if we supply

only 40 thermal units, we get only one-half the ice melted. If

only 10 units are supplied, then we get only one eighth of a

kilogram of water, and no more nor less.

I have ventured to recall to you these commonplaces of science

before considering a mode of melting ice which is less generally

known, and which involves no supply of heat on your part. This

method involves for its

266

understanding a careful consideration of the thermal properties

of water in the solid state.

It must have been observed a very long time ago that water

expands when it freezes. Otherwise ice would not float on water;

and, what is perhaps more important in your eyes, your water

pipes would not burst in winter when the water freezes therein.

But although the important fact of the expansion of water on

freezing was so long presented to the observation of mankind, it

was not till almost exactly the middle of the last century that

James Thomson, a gifted Irishman, predicted many important

consequences arising from the fact of the expansion of water on

becoming solid. The principles lie enunciated are perfectly

general, and apply in every case of change of volume attending

change of state. We are here only concerned with the case of

water and ice.

James Thomson, following a train of thought which we cannot here

pursue, predicted that owing to the fact of the expansion of

water on becoming solid, pressure will lower the melting point of

ice or the freezing point of water. Normally, as you are aware,

the temperature is 0° C. or 32° F. Thomson said that this would

be found to be the freezing point only at atmospheric pressure.

He calculated how much it would change with change of pressure.

He predicted that the freezing point would fall 0.0075 of a

degree Centigrade for each additional atmosphere of pressure

applied to the water. Suppose,

267

for instance, our earth possessed an atmosphere so heavy to as

exert a thousand times the pressure of the existing atmosphere,

then water would not freeze at 0° C., but at -7.5° C. or about

18° F. Again, in vacuo, that is when the pressure has been

reduced to the relatively small vapour pressure of the water, the

freezing point is above 0° C., _i.e._ at 0.0075° C. In parts of

the ocean depths the pressure is much over a thousand

atmospheres. Fresh water would remain liquid there at

temperatures much below 0° C.

It will be evident enough, even to those not possessed of the

scientific insight of James Thomson, that some such fact is to be

anticipated. It is, however, easy to be wise after the event. It

appeals to us in a general way that as water expands on freezing,

pressure will tend to resist the turning of it to ice. The water

will try to remain liquid in obedience to the pressure. It will,

therefore, require a lower temperature to induce it to become

ice.

James Thomson left his thesis as a prediction. But he predicted

exactly what his distinguished brother, Sir William Thomson—later

Lord Kelvin—found to happen when the matter was put to the test

of experiment. We must consider the experiment made by Lord

Kelvin.

According to Thomson's views, if a quantity of ice and water are

compressed, there must be _a fall of temperature_. The nature of

his argument is as follows:

268

Let the ice and water be exactly at 0° C. to start with. Then

suppose we apply, say, one thousand atmospheres pressure. The

melting point of the ice is lowered to -7.5° C. That is, it will

require a temperature so low as -7.5° C. to keep it solid. It

will therefore at once set about melting, for as we have seen,

its actual temperature is not -7.5° C., but a higher temperature,

_i.e._ 0° C. In other words, it is 7.5° above its melting point.

But as soon as it begins melting it also begins to absorb heat to

supply the 80 thermal units which, as we know, are required to

turn each kilogram of the ice to water. Where can it get this

heat? We assume that we give it none. It has only two sources,

the ice can take heat from itself, and it can take heat from the

water. It does both in this case, and both ice and water drop in

temperature. They fall in temperature till -7.5° is reached. Then

the ice has got to its melting point under the pressure of one

thousand atmospheres, or, as we may put it, the water has reached

its freezing point. There can be no more melting. The whole mass

is down to -7.5° C., and will stay there if we keep heat from

flowing either into or out of the vessel. There is now more water

and less ice in the vessel than when we started, and the

temperature has fallen to -7.5° C. The fall of temperature to the

amount predicted by the theory was verified by Lord Kelvin.

Suppose we now suddenly remove the pressure; what will happen? We

have water and ice at -7.5° C.

269

and at the normal pressure. Water at -7.5° and at the normal

pressure of course turns to ice. The water will, therefore,

instantly freeze in the vessel, and the whole process will be

reversed. In freezing, the water will give up its latent heat,

and this will warm up the whole mass till once again 0° C. is

attained. Then there will be no more freezing, for again the ice

is at its melting point. This is the remarkable series of events

which James Thomson predicted. And these are the events which

Lord Kelvin by a delicate series of experiments, verified in

every respect.

Suppose we had nothing but solid ice in the vessel at starting,

would the experiment result in the same way? Yes, it assuredly

would. The ice under the increased pressure would melt a little

everywhere throughout its mass, taking the requisite latent heat

from itself at the expense of its sensible heat, and the

temperature of the ice would fall to the new melting point.

Could we melt the whole of the ice in this manner? Again the

answer is "yes." But the pressure must be very great. If we

assume that all the heat is obtained at the expense of the

sensible heat of the ice, the cooling must be such as to supply

the latent heat of the whole mass of water produced. However, the

latent heat diminishes as the melting point is lowered, and at a

rate which would reduce it to nothing at about 18,000

atmospheres. Mousson, operating on ice enclosed in a conducting

cylinder and cooled to -18° at starting

270

appears to have obtained very complete liquefaction. Mousson must

have attained a pressure of at least an amount adequate to lower

the melting point below -18°. The degree of liquefaction actually

attained may have been due in part to the passage of heat through

the walls of the vessel. He proved the more or less complete

liquefaction of the ice within the vessel by the fall of a copper

index from the top to the bottom of the vessel while the pressure

was on.

I have here a simple way of demonstrating to you the fall of

temperature attending the compression of ice. In this mould,

which is strongly made of steel, lined with boxwood to diminish

the passage of conducted heat, is a quantity of ice which I

compress when I force in this plunger. In the ice is a

thermoelectric junction, the wires leading to which are in

communication with a reflecting galvanometer. The thermocouple is

of copper and nickel, and is of such sensitiveness as to show by

motion of the spot of light on the screen even a small fraction

of a degree. On applying the pressure, you see the spot of light

is displaced, and in such a direction as to indicate cooling. The

balancing thermocouple is all the time imbedded in a block of ice

so that its temperature remains unaltered. On taking off the

pressure, the spot of light returns to its first position. I can

move the spot of light backwards and forwards on the screen by

taking off and putting on the pressure. The effects are quite

instantaneous.

271

The fact last referred to is very important. The ice, in fact, is

as it were automatically turned to water. It is not a matter of

the conduction of heat from point to point in the ice. Its own

sensible heat is immediately absorbed throughout the mass. This

would be the theoretical result, but it is probable that owing to

imperfections throughout the ice and failure in uniformity in the

distribution of the stress, the melting would not take place

quite uniformly or homogeneously.

Before applying our new ideas to skating, I want you to notice a

fact which I have inferentially stated, but not specifically

mentioned. Pressure will only lead to the melting of ice if the

new melting point, _i.e._ that due to the pressure, is below the

prevailing temperature. Let us take figures. The ice to start

with is, say, at -3° C. Suppose we apply such a pressure to this

ice as will confer a melting point of -2° C. on it. Obviously,

there will be no melting. For why should ice which is at -3° C.

melt when its melting point is -2° C.? The ice is, in fact,

colder than its melting point. Hence, you note this fact: The

pressure must be sufficiently intense to bring the melting point

below the prevailing temperature, or there will be no melting;

and the further we reduce the melting point by pressure below the

prevailing temperature, the more ice will be melted.

We come at length to the object of our remarks I don't know who

invented skating or skates. It is said that in the thirteenth

century the inhabitants of

272

England used to amuse themselves by fastening the bones of an

animal beneath their feet, and pushing themselves about on the

ice by means of a stick pointed with iron. With such skates, any

performance either on inside or outside edge was impossible. We

are a conservative people. This exhilarating amusement appears to

have served the people of England for three centuries. Not till

1660 were wooden skates shod with iron introduced from the

Netherlands. It is certain that skating was a fashionable

amusement in Pepys' time. He writes in 1662 to the effect: "It

being a great frost, did see people sliding with their skates,

which is a very pretty art." It is remarkable that it was the

German poet Klopstock who made skating fashionable in Germany.

Until his time, the art was considered a pastime, only fit for

very young or silly people.

I wish now to dwell upon that beautiful contrivance the modern

skate. It is a remarkable example of how an appliance can develop

towards perfection in the absence of a really intelligent

understanding of the principles underlying its development. For

what are the principles underlying the proper construction of the

skate? After what I have said, I think you will readily

understand. The object is to produce such a pressure under the

blade that the ice will melt. We wish to establish such a

pressure under the skate that even on a day when the ice is below

zero, its melting

273

point is so reduced just under the edge of the skate that the ice

turns to water.

It is this melting of the ice under the skate which secures the

condition essential to skating. In the first place, the skate no

longer rests on a solid. It rests on a liquid. You are aware how

in cases where we want to reduce friction—say at the bearing of a

wheel or under a pivot—we introduce a liquid. Look at the

bearings of a steam engine. A continuous stream of oil is fed in

to interpose itself between the solid surfaces. I need not

illustrate so well-known a principle by experiment. Solid

friction disappears when the liquid intervenes. In its place we

substitute the lesser difficulty of shearing one layer of the

liquid over the other; and if we keep up the supply of oil the

work required to do this is not very different, no matter how

great we make the pressure upon the bearings. Compared with the

resistance of solid friction, the resistance of fluid friction is

trifling. Here under the skate the lubrication is perhaps the

most perfect which it is possible to conceive. J. Müller has

determined the coefficient by towing a skater holding on by a

spring balance. The coefficient is between 0.016 and 0.032. In

other words, the skater would run down an incline so little as 1

or 2 degrees; an inclination not perceivable by the eye. Now

observe that the larger of these coefficients is almost exactly

the same as that which Perry found in the case of well-greased

surfaces. But evidently no

274

artificial system of lubrication could hope to equal that which

exists between the skate and the ice. For the lubrication here

is, as it were, automatic. In the machine if the lubricant gets

squeezed out there instantly ensues solid friction. Under the

skate this cannot happen for the squeezing out of the lubricant

is instantly followed by the formation of another film of water.

The conditions of pressure which may lead to solid friction in

the machine here automatically call the lubricant into

existence.

Just under the edge of the skate the pressure is enormous.

Consider that the whole weight of the skater is born upon a mere

knife edge. The skater alternately throws his whole weight upon

the edge of each skate. But not only is the weight thus

concentrated upon one edge, further concentration is secured in

the best skates by making the skate hollow-ground, _i.e._

increasing the keenness of the edge by making it less than a

right angle. Still greater pressure is obtained by diminishing

the length of that part of the blade which is in contact with the

ice. This is done by putting curvature on the blade or making it

what is called "hog-backed." You see that everything is done to

diminish the area in contact with the ice, and thus to increase

the pressure. The result is a very great compression of the ice

beneath the edge of the skate. Even in the very coldest weather

melting must take place to some extent.

As we observed before, the melting is instantaneous,

275

Heat has not to travel from one point of the ice to another;

immediately the pressure comes on the ice it turns to water. It

takes the requisite heat from itself in order that the change of

state may be accomplished. So soon as the skate passes on, the

water resumes the solid state. It is probable that there is an

instantaneous escape, and re-freezing of some of the water from

beneath the skate, the skate instantly taking a fresh bearing and

melting more ice. The temperature of the water escaping from

beneath the skate, or left behind by it, immediately becomes what

it was before the skate pressed upon it.

Thus, a most wonderful and complex series of molecular events

takes place beneath the skate. Swift as it passes, the whole

sequence of events which James Thomson predicted has to take

place beneath the blade Compression; lowering of the melting

point below the temperature of the surrounding ice; melting;

absorption of heat; and cooling to the new melting point, _i.e._

to that proper to the pressure beneath the blade. The skate now

passes on. Then follow: Relief of pressure; re-solidification of

the water; restoration of the borrowed heat from the congealing

water and reversion of the ice to the original temperature.

If we reflect for a moment on all this, we see that we do not

skate on ice but on water. We could not skate on ice any more

than we could skate on glass. We saw that with light weights and

when the pressure

276

{Diagram}

Diagram showing successive states obtaining in ice, before,

during, and after the passage of the skate. The temperatures and

pressures selected for illustration are such as might occur under

ordinary conditions. The edge of the skate is shown in magnified

cross-section.

277

Was not sufficient to melt the ice, the friction was much the

same as that of metal on glass. Ice is not slippery. It is an

error to say that it is. The learned professor was very much

astray when he said that you could skate on ice because it is so

smooth. The smoothness of the ice has nothing to do with the

matter. In short, owing to the action of gravity upon your body,

you escape the normal resistance of solid on solid, and glide

about with feet winged like the messenger of the Gods; but on

water.

A second condition essential to the art of skating is also

involved in the melting of the ice. The sinking of the skate

gives the skater "bite." This it is which enables him to urge

himself forward. So long as skates consisted of the rounded bones

of animals, the skater had to use a pointed staff to propel

himself. In creating bite, the skater again unconsciously appeals

to the peculiar physical properties of ice. The pressure required

for the propulsion of the skater is spread all along the length

of the groove he has cut in the ice, and obliquely downwards. The

skate will not slip away laterally, for the horizontal component

of the pressure is not enough to melt the ice. He thus gets the

resistance he requires.

You see what a very perfect contrivance the skate is; and what a

similitude of intelligence there is in its evolution. Blind

intelligence, because it is certain the true physics of skating

was never held in view by

278

the makers of skates. The evolution of the skate has been truly

organic. The skater selected the fittest skate, and hence the fit

skate survived.

In a word, the possibility of skating depends on the dynamical

melting of ice under pressure. And observe the whole matter turns

upon the apparently unrelated fact that the freezing of water

results in a solid more bulky than the water which gives rise to

it. If ice was less bulky than the water from which it was

derived, pressure would not melt it; it would be all the more

solid for the pressure, as it were. The melting point would rise

instead of falling. Most substances behave in this manner, and

hence we cannot skate upon them. Only quite a few substances

expand on freezing, and it happens that their particular melting

temperatures or other properties render them unsuitable to

skating. The most abundant fluid substance on the earth, and the

most abundant substance of any one kind on its surface, thus

possesses the ideally correct and suitable properties for the art

of skating.

I have pointed out that the pressure must be such as to bring the

temperature of melting below that prevailing in the ice at the

time. We have seen also, that one atmosphere lowers the melting

point of ice by the 1/140 of a degree Centigrade; more exactly by

0.0075°. Let us now assume that the skate is so far sunken in the

ice as to bear for a length of two inches, and for a width of

one-hundredth of an inch. The skater weighs,

279

let us say—150 pounds. If this weight was borne on one square

inch, the pressure would be ten atmospheres. But the skater rests

his weight, in fact, upon an area of one-fiftieth of an inch. The

pressure is, therefore, fifty times as great. The ice is

subjected to a pressure of 500 atmospheres. This lowers the

melting point to -3.75° C. Hence, on a day when the ice is at

this temperature, the skate will sink in the ice till the weight

of the skater is concentrated as we have assumed. His skate can

sink no further, for any lesser concentration of the pressure

will not bring the melting point below the prevailing

temperature. We can calculate the theoretical bite for any state

of the ice. If the ice is colder the bite will not be so deep. If

the temperature was twice as far below zero, then the area over

which the skater's weight will be distributed, when the skate has

penetrated its maximum depth, will be only half the former area,

and the pressure will be one thousand atmospheres.

An important consideration arises from the fact that under the

very extreme edge of the skate the pressure is indefinitely

great. For this involves that there will always be some bite,

however cold the ice may be. That is, the narrow strip of ice

which first receives the skater's weight must partially liquefy

however cold the ice.

It must have happened to many here to be on ice which was too

cold to skate on with comfort. The

280

skater in this case speaks of the ice as too hard. In the

Engadine, the ice on the large lakes gets so cold that skaters

complain of this. On the rinks, which are chiefly used there, the

ice is frequently renewed by flooding with water at the close of

the day. It thus never gets so very cold as on the lakes. I have

been on ice in North France, which, in the early morning, was too

hard to afford sufficient bite for comfort. The cause of this is

easily understood from what we have been considering.

We may now return to the experimental results which we obtained

early in the lecture. The heavy weights slip off the ice at a low

angle because just at the points of contact with the ice the

latter melts, and they, in fact, slip not on ice but on water.

The light weights on cold, dry ice do not lower the melting point

below the temperature of the ice, _i.e._ below -10° C., and so

they slip on dry ice. They therefore give us the true coefficient

of friction of metal on ice.

This subject has, more recently been investigated by H. Morphy,

of Trinity College, Dublin. The refinement of a closed vessel at

uniform temperature, in which the ice is formed and the

experiment carried out, is introduced. Thermocouples give the

temperatures, not only of the ice but of the aluminium sleigh

which slips upon it under various loads. In this way we may be

certain that the metal runners are truly at the temperature of

the ice. I now quote from Morphy's paper

281

"The angle of friction was found to remain constant until a

certain stage of the loading, when it suddenly fell to about half

of its original value. It then remained constant for further

increases in the load.

"These results, which confirmed those obtained previously with

less satisfactory apparatus, are shown in the table below. In the

first column is shown the load, _i.e._ the weight of sleigh +

weight of shot added. In the second and third columns are shown,

respectively, the coefficient and angle of friction, whilst the

fourth gives the temperature of the ice as determined from the

galvanometer deflexions.

Load.        Tan y.          y.        Temp.

5.68 grams.  0.36±.01     20°±30'    -5.65° C.

10.39                                -5.65°

11.96                                -5.75°

12.74                                -5.60°

13.53                                -5.65°

14.31                                -5.65°

15.10 grams. 0.17±.01    9°.30'±30'  -5.60°

16.67                                -5.55°

19.81                                -5.60°

24.52                                -5.60°

5.68 grams. 0.36±.01      20°±30'    -5.60°

"These experiments were repeated on another occasion with the same

result and similar results had been obtained with different

apparatus.

"As a result of the investigation the following points are

clearly shown:—

282

"(1) The coefficient of friction for ice at constant temperature

may have either of two constant values according to the pressure

per unit surface of contact.

"(2) For small pressures, and up to a certain well defined limit

of pressure, the coefficient is fairly large, having the value

0.36±.01 in the case investigated.

"(3) For pressures greater than the above limit the coefficient

is relatively small, having the value 0.17±.01 in the case

investigated."

It will be seen that Morphy's results are similar to those

arrived at in the first experimental consideration of our

subject; but from the manner in which the experiments have been

carried out, they are more accurate and reliable.

A great deal more might be said about skating, and the allied

sports of tobogganing, sleighing, curling, ice yachting, and

last, but by no means least, sliding—that unpretentious pastime

of the million. Happy the boy who has nails in his boots when

Jack-Frost appears in his white garment, and congeals the

neighbouring pond. But I must turn away at the threshold of the

humorous aspect of my subject (for the victim of the street

"slide" owes his injured dignity to the abstruse laws we have

been discussing) and pass to other and graver subjects intimately

connected with skating.

James Thomson pointed out that if we apply compressional stress

to an ice crystal contained in a vessel

283

which also contains other ice crystals, and water at 0° C., then

the stressed crystal will melt and become water, but its

counterpart or equivalent quantity of ice will reappear elsewhere

in the vessel. This is, obviously, but a deduction from the

principles we have been examining. The phenomenon is commonly

called "regelation." I have already made the usual regelation

experiment before you when I compressed broken ice in this mould.

The result was a clear, hard and almost flawless lens of ice. Now

in this operation we must figure to ourselves the pieces of ice

when pressed against one another melting away where compressed,

and the water produced escaping into the spaces between the

fragments, and there solidifying in virtue of its temperature

being below the freezing point of unstressed water. The final

result is the uniform lens of ice. The same process goes on in a

less perfect manner when you make—or shall I better say—when you

made snowballs.

We now come to theories of glacier motion; of which there are

two. The one refers it mainly to regelation; the other to a real

viscosity of the ice.

The late J. C. M'Connel established the fact that ice possesses

viscosity; that is, it will slowly yield and change its shape

under long continued stresses. His observations, indeed, raise a

difficulty in applying this viscosity to explain glacier motion,

for he showed that an ice crystal is only viscous in a certain

structural

284

direction. A complex mixture of crystals such, as we know glacier

ice to be, ought, we would imagine, to display a nett or

resultant rigidity. A mass of glacier ice when distorted by

application of a force must, however, undergo precisely the

transformations which took place in forming the lens from the

fragments of ice. In fact, regelation will confer upon it all the

appearance of viscosity.

Let us picture to ourselves a glacier pressing its enormous mass

down a Swiss valley. At any point suppose it to be hindered in

its downward path by a rocky obstacle. At that point the ice

turns to water just as it does beneath the skate. The cold water

escapes and solidifies elsewhere. But note this, only where there

is freedom from pressure. In escaping, it carries away its latent

heat of liquefaction, and this we must assume, is lost to the

region of ice lately under pressure. This region will, however,

again warm up by conduction of heat from the surrounding ice, or

by the circulation of water from the suxface. Meanwhile, the

pressure at that point has been relieved. The mechanical

resistance is transferred elsewhere. At this new point there is

again melting and relief of pressure. In this manner the glacier

may be supposed to move down. There is continual flux of

conducted heat and converted latent heat, hither and thither, to

and from the points of resistance. The final motion of the whole

mass is necessarily slow; a few feet in the day or, in winter,

285

even only a few inches. And as we might expect, perfect silence

attends the downward slipping of the gigantic mass. The motion

is, I believe, sufficiently explained as a skating motion. The

skate is, however, fixed, the ice moves. The great Aletsch

Glacier collects its snows among the highest summits of the

Oberland. Thence, the consolidated ice makes its way into the

Rhone Valley, travelling a distance of some 20 miles. The ice now

melting into the youthful Rhone fell upon the Monch, the Jungfrau

or the Eiger in the days when Elizabeth ruled in England and

Shakespeare lived.

The ice-fall is a common sight on the glacier. In great lumps and

broken pinnacles it topples over some rocky obstacle and falls

shattered on to the glacier below. But a little further down the

wound is healed again, and regelation has restored the smooth

surface of the glacier. All such phenomena are explained on James

Thomson's exposition of the behaviour of a substance which

expands on passing from the liquid to the solid state.

We thus have arrived at very far-reaching considerations arising

out of skating and its science. The tendency for snow to

accumulate on the highest regions of the Earth depends on

principles which we cannot stop to consider. We know it collects

above a certain level even at the Equator. We may consider, then,

that but for the operation of the laws which James Thomson

brought to light, and which his illustrious brother,

286

Lord Kelvin, made manifest, the uplands of the Earth could not

have freed themselves of the burthen of ice. The geological

history of the Earth must have been profoundly modified. The

higher levels must have been depressed; the general level of the

ocean relatively to the land thereby raised, and, it is even

possible, that such a mean level might have been attained as

would result in general submergence.

During the last great glacial period, we may say the fate of the

world hung on the operation of those laws which have concerned us

throughout this lecture. It is believed the ice was piled up to a

height of some 6,000 feet over the region of Scandinavia. Under

the influence of the pressure and fusion at points of resistance,

the accumulation was stayed, and it flowed southwards the

accumulation was stayed, and it flowed southwards over Northern

Europe. The Highlands of Scotland were covered with, perhaps,

three or four thousand feet of ice. Ireland was covered from

north to south, and mighty ice-bergs floated from our western and

southern shores.

The transported or erratic stones, often of great size, which are

found in many parts of Ireland, are records of these long past

events: events which happened before Man, as a rational being,

appeared upon the Earth.

287

A SPECULATION AS TO A PREMATERIAL UNIVERSE [1]

"And therefore...these things likewise had a birth; for things

which are of mortal body could not for an infinite time back...

have been able to set at naught the puissant strength of

immeasurable age."—LUCRETIUS, _De Rerum Natura._

"O fearful meditation! Where, alack! Shall Time's best jewel

from Time's chest lie hid?" —SHAKESPEARE.

IN the material universe we find presented to our senses a

physical development continually progressing, extending to all,

even the most minute, material configurations. Some fundamental

distinctions existing between this development as apparent in the

organic and the inorganic systems of the present day are referred

to elsewhere in this volume.[2] In the present essay, these

systems as having a common origin and common ending, are merged

in the same consideration as to the nature of the origin of

material systems in general. This present essay is occupied by

the consideration of the necessity of limiting material

interactions in past time. The speculation originated in the

difficulties which present themselves when we ascribe to these

interactions infinite duration in the past. These difficulties

first claim our consideration.

[1] Proc. Royal Dublin Soc., vol. vii., Part V, 1892.

[2] _The Abundance of Life._

288

Accepting the hypothesis of Kant and Laplace in its widest

extension, we are referred to a primitive condition of wide

material diffusion, and necessarily too of material instability.

The hypothesis is, in fact, based upon this material instability.

We may pursue the sequence of events assumed in this hypothesis

into the future, and into the past.

In the future we find finality to progress clearly indicated. The

hypothesis points to a time when there will be no more

progressive change but a mere sequence of unfruitful events, such

as the eternal uniform motion of a mass of matter no longer

gaining or losing heat in an ether possessed of a uniform

distribution of energy in all its parts. Or, again, if the ether

absorb the energy of material motion, this vast and dark

aggregation eternally poised and at rest within it. The action is

transferred to the subtle parts of the ether which suffer none of

the energy to degrade. This is, physically, a thinkable future.

Our minds suggest no change, and demand none. More than this,

change is unthinkable according to our present ideas of energy.

Of progress there is an end.

This finality _â parte post_ is instructive. Abstract

considerations, based on geometrical or analytical illustrations,

question the finiteness of some physical developments. Thus our

sun may require eternal time to attain the temperature of the

ether around it, the approach to this condition being assumed to

be asymptotic in

289

character. But consider the legitimate _reductio ad absurdum_ of

an ember raked from a fire 1000 years ago. Is it not yet cooled

down to the constant temperature of its surroundings? And we may

evidently increase the time a million-fold if we please. It

appears as if we must regard eternity as outliving every

progressive change, For there is no convergence or enfeeblement

of time. The ever-flowing present moves no differently for the

occurrence of the mightiest or the most insignificant events. And

even if we say that time is only the attendant upon events, yet

this attendant waits patiently for the end, however long

deferred.

Does the essentially material hypothesis of Kant and Laplace

account for an infinite past as thinkably as it accounts for the

infinite future? As this hypothesis is based upon material

instability the question resolves itself into this:— Is the

assumption of an infinitely prolonged past instability a probable

or possible account of the past? There are, it appears to me,

great difficulties involved in accepting the hypothesis of

infinitely prolonged material instability. I will refer here to

three principal objections. The first may be called a

metaphysical objection; the second is partly metaphysical and

partly physical, the third may be considered a physical

objection, as it is involved directly in the phenomena presented

by our universe.

The metaphysical objection must have presented itself to every

one who has considered the question. It may

290

be put thus:—If present events are merely one stage in an

infinite progress, why is not the present stage long ago passed

over? We are evidently at liberty to push back any stage of

progress to as remote a period as we like by putting back first

the one before this and next the stage preceding this, and so on,

for, by hypothesis, there is no beginning to the progress.

Thus, the sum of passing events constituting the present universe

should long ago have been accomplished and passed away. If we

consider alternative hypotheses not involving this difficulty, we

are at once struck by the fact that the future of material

development is free of the objection. For the eternity of

unprogressive events involved in the future on Kant's hypothesis,

is not only thinkable, but any change is, as observed,

irreconcilable with our ideas of energy. As in the future so in

the past we look to a cessation to progress. But as we believe

the activity of the present universe must in some form have

existed all along, the only refuge in the past is to imagine an

active but unprogressive eternity, the unprogressive activity at

some period becoming a progressive activity—that progressive

activity of which we are spectators. To the unprogressive

activity there was no beginning; in fact, beginning is as

unthinkable and uncalled for to the unprogressive activity of the

past as ending is to the unprogressive activity of the future,

when all developmental actions shall have ceased. There is no

beginning or ending to the activity of the universe.

291

There is beginning and ending to present progressive activity.

Looking through the realm of nature we seek beginning and ending,

but "passing through nature to eternity" we find neither. Both

are justified; the questioning of the ancient poet regarding the

past, and of the modern regarding the future, quoted at the head

of this essay.

The next objection, which is in part metaphysical, is founded on

the difficulty of ascribing any ultimate reality or potency to

forces diminishing through eternal time. Thus, against the

assumption that our universe is the result of material

aggregation progressing over eternal time, which involves the

primitive infinite separation of the particles, we may ask, what

force can have acted between particles sundered by infinite

distance? The gravitational force falling off as the square of

the distance, must vanish at infinity if we mean what we say when

we ascribe infinite separation to them. Their condition is then

one of neutral stability, a finite movement of the particles

neither increasing nor diminishing interaction. They had then

remained eternally in their separated condition, there being no

cause to render such condition finite. The difficulty involved

here appears to me of the same nature as the difficulty of

ascribing any residual heat to the sun after eternal time has

elapsed. In both cases we are bound to prolong the time, from our

very idea of time, till progress is no more, when in the one case

we can imagine no mutual approximation of the

292

particles, in the other no further cooling of the body. However,

I will riot dwell further upon this objection, as it does not, I

believe, present itself with equal force to every mind. A reason

less open to dispute, as being less subjective, against the

aggregation of infinitely remote particles as the origin of our

universe, is contained in the physical objection.

In this objection we consider that the appearance presented by

our universe negatives the hypothesis of infinitely prolonged

aggregation. We base this negation upon the appearance of

simultaneity ~ presented by the heavens, contending that this

simultaneity is contrary to what we would expect to find in the

case of particles gathered from infinitely remote distances.

Whether these particles were endowed with relative motions or not

is unimportant to the consideration. In what respects do the

phenomena of our universe present the appearance of simultaneous

phenomena? We must remember that the suns in space are as fires

which brighten only for a moment and are then extinguished. It is

in this sense we must regard the longest burning of the stars.

Whether just lit or just expiring counts little in eternity. The

light and heat of the star is being absorbed by the ether of

space as effectually and rapidly as the ocean swallows the ripple

from the wings of an expiring insect. Sir William Herschel says

of the galaxy of the milky way:— "We do not know the rate of

progress of this mysterious chronometer, but it is nevertheless

certain that it cannot

293

last for ever, and its past duration cannot be infinite." We do

not know, indeed, the rate of progress of the chronometer, but if

the dial be one divided into eternal durations the consummation

of any finite physical change represents such a movement of the

hand as is accomplished in a single vibration of the balance

wheel.

Hence we must regard the hosts of glittering stars as a

conflagration that has been simultaneously lighted up in the

heavens. The enormous (to our ideas) thermal energy of the stars

resembles the scintillation of iron dust in a jar of oxygen when

a pinch of the dust is thrown in. Although some particles be

burnt up before others become alight, and some linger yet a

little longer than the others, in our day's work the

scintillation of the iron dust is the work of a single instant,

and so in the long night of eternity the scintillation of the

mightiest suns of space is over in a moment. A little longer,

indeed, in duration than the life which stirs a moment in

response to the diffusion of the energy, but only very little. So

must an Eternal Being regard the scintillation of the stars and

the periodic vibration of life in our geological time and the

most enduring efforts of thought. The latter indeed are no more

lasting than

"... the labour of ants In the light of a million million of

suns."

But the myriad suns themselves, with their generations, are the

momentary gleam of lights for ever after extinguished.

294

Again, science suggests that the present process of material

aggregation is not finished, and possibly will only be when it

prevails universally. Hence the very distribution of the stars,

as we observe them, as isolated aggregations, indicates a

development which in the infinite duration must be regarded as

equally advanced in all parts of stellar space and essentially a

simultaneous phenomenon. For were we spectators of a system in

which any very great difference of age prevailed, this very great

difference would be attended by some such appearance as the

following:—

The aupearance of but one star, other generations being long

extinct or no others yet come into being; or, perhaps, a faint

nebulous wreath of aggregating matter somewhere solitary in the

heavens; or no sign of matter beyond our system, either because

ungathered or long passed away into darkness.[1]

Some such appearances were to be expected had the aggregation of

matter depended solely on chance encounters of particles

scattered through infinite space.

For as, by hypothesis, the aggregation occupies an infinite time

in consummation it is nearly a certainty that each particle

encountered after immeasurable time, and then for the first time

endowed with actual gravitational potential energy, would have

long expended this energy

[1] It is interesting to reflect upon the effect which an entire

absence of luminaries outside our solar system would have had

upon the views of our philosophers and upon our outlook on life.

295

before another particle was gathered. But the fact that so many

fires which we know to be of brief duration are scattered through

a region of space, and the fact of a configuration which we

believe to be a transitory ore, suggest their simultaneous

aggregation here and there. And in the nebulous wreaths situated

amidst the stars there is evidence that these actually originated

where they now are, for in such no relative motion, I believe,

has as yet been detected by the spectroscope. All this, too, is

in keeping with the nebular hypothesis of Kant and Laplace so

long as this does not assume a primitive infinite dispersion of

matter, but the gathering of matter from finite distances first

into nebulous patches which aggregating with each other have

given rise to our system of stars. But if we extend this

hypothesis throughout an infinite past by the supposition of

aggregation of infinitely remote particles we replace the

simultaneous approach required in order to accotnt for the

simultaneous phenomena visible in the heavens, by a succession of

aggregative events, by hypothesis at intervals of nearly infinite

duration, when the events of the universe had consisted of fitful

gleams lighted after eternities of time and extinguished for yet

other eternities.

Finally, if we seek to replace the eternal instability involved

in Kant's hypothesis when extended over an infinite past, by any

hypothesis of material stability, we at once find ourselves in

the difficulty that from the known properties of matter such

stability must have been

296

permanent if ever existent, which is contrary to fact. Thus the

kinetic inertia expressed in Newton's first law of motion might

well be supposed to secure equilibrium with material attraction,

but if primevally diffused matter had ever thus been held in

equilibrium it must have remained so, or it was maintained so

imperfectly, which brings us back to endless evolution.

On these grounds I contend that the present gravitational

properties of matter cannot be supposed to have acted for all

past duration. Universal equilibrium of gravitating particles

would have been indestructible by internal causes. Perpetual

instability or evolution is alike unthinkable and contrary to the

phenomena of the universe of which we are cognisant. We therefore

turn from gravitating matter as affording no rational account of

the past. We do so of necessity, however much we feel our

ignorance of the nature of the unknown actions to which we have

recourse.

A prematerial condition of the universe was, we assume, a

condition in which uniformity as regards the average distribution

of energy in space prevailed, but neterogeneity and instability

were possible. The realization of that possibility was the

beginning we seek, and we today are witnesses of the train of

events involved in the breakdown of an eternal past equilibrium.

We are witnesses on this hypothesis, of a catastrophe possibly

confined to certain regions of space, but which is, to the

motions and configurations concerned, absolutely unique,

reversible to

297

its former condition of potential by no process of which we can

have any conception.

Our speculation is that we, as spectators of evolution, are

witnessing the interaction of forces which have not always been

acting. A prematerial state of the universe was one of unfruitful

motions, that is, motions unattended by progressing changes, in

our region of the ether. How extended we cannot say; the nature

of the motions we know not; but the kinetic entities differed

from matter in the one important particular of not possessing

gravitational attraction. Such kinetic configurations we cannot

consider to be matter. It was _possible_ to construct matter by

their summation or linkage as the configuration of the crystal is

possible in the clear supersaturated liquid.

Duration in an ether filled with such motions would pass in a

succession of mere unfruitful events; as duration, we may

imagine, even now passes in parts of the ether similar to our

own. An endless (it may be) succession of unprogressive,

fruitless events. But at one moment in the infinite duration the

requisite configuration of the elementary motions is attained;

solely by the one chance disposition the stability of all must

go, spreading from the fateful point.

Possibly the material segregation was confined to one part of

space, the elementary motions condensing upon transformation, and

so impoverishing the ether around till the action ceased. Again

in the same sense as the

298

stars are simultaneous, so also they may be regarded as uniform

in size, for the difference in magnitude might have been anything

we please to imagine, if at the same time we ascribe sufficient

distance sundering great and small. So, too;, will a dilute

solution of acetate of soda build a crystal at one point, and the

impoverishment of the medium checking the growth in this region,

another centre will begin at the furthest extremities of the

first crystal till the liquid is filled with loose feathery

aggregations comparable in size with one another. In a similar

way the crystallizing out of matter may have given rise, not to a

uniform nebula in space, but to detached nebula, approximately of

equal mass, from which ultimately were formed the stars.

That an all-knowing Being might have foretold the ultimate event

at any preceding period by observing the motions of the parts

then occurring, and reasoning as to the train of consequences

arising from these nations, is supposable. But considerations

arising from this involve no difficulty in ascribing to this

prematerial train of events infinite duration. For progress there

is none, and we can quite as easily conceive of some part of

space where the same Infinite Intelligence, contemplating a

similar train of unfruitful motions, finds that at no time in the

future will the equilibrium be disturbed. But where evolution is

progressing this is no longer conceivable, as being contradictory

to the very idea of progressive development. In this case

Infinite Intelligence

299

_necessarily_ finds, as the result of his contemplation, the

aggregation of matter, and the consequences arising therefrom.

The negation of so primary a material property as gravitation to

these primitive motions of (or in) the ether, probably involves

the negation of many properties we find associated with matter.

Possibly the quality of inertia, equally primary, is involved

with that of gravitation, and we may suppose that these two

properties so intimately associated in determining the motions of

bodies in space were conferred upon the primitive motions as

crystallographic attraction and rigidity are first conferred upon

the solid growing from the supersaturated liquid. But in some

degree less speculative is the supposition that the new order of

motions involved the transformation of much energy into the form

of heat vibrations; so that the newly generated matter, like the

newly formed crystal, began its existence in a medium richly fed

with thermal radiant energy. We may consider that the thermal

conditions were such as would account for a primitive

dissociation of the elements. And, again, we recall how the

physicist finds his estimate of the energy involved in mere

gravitational aggregation inadequate to afford explanation of

past solar heat. It is supposable, on such a hypothesis as we

have been dwelling on, that the entire subsequent gravitational

condensation and conversion of material potential energy, dating

from the first formation of matter to the stage of star

formation

300

may be insignificant in amount compared with the conversion of

etherial energy attending the crystallizing out of matter from

the primitive motions. And thus possibly the conditions then

obtaining involved a progressively increasing complexity of

material structure the genesis of the elements, from an

infra-hydrogen possessing the simplest material configuration,

resulting ultimately in such self-luminous nebula as we yet see

in the heavens.

The late James Croll, in his _Stellar Evolution_, finds objections

to an eternal evolution, one of which is similar to the

"metaphysical" objection urged in this paper. His way out of the

difficulty is in the speculation that our stellar system

originated by the collision of two masses endowed with relative

motion, eternal in past duration, their meeting ushering in the

dawn of evolution. However, the state of aggregation here

assumed, from the known laws of matter and from analogy, calls

for explanation as probably the result of prior diffusion, when,

of course, the difficulty is only put back, not set at rest. Nor

do I think the primitive collision in harmony with the number of

relatively stationary nebula visible in space.

The metaphysical objection is, I find, also urged by George

Salmon, late Provost of Trinity College, in favour of the

creation of the universe.—(_Sermons on Agnosticism_.)

A. Winchell, in _World Life_, says: "We have not

301

the slightest scientific grounds for assuming that matter existed

in a certain condition from all eternity. The essential activity

of the powers ascribed to it forbids the thought; for all that we

know, and, indeed, as the _conclusion_ from all that we know,

primal matter began its progressive changes on the morning of its

existence."

Finally, in reference to the hypothesis of a unique determination

of matter after eternal duration in the past, it may not be out

of place to remind the reader of the complexity which modern

research ascribes to the structure of the atom.

302

INDEX

A.

Abney, Sir Wm., on sensitisers, 210.

Abundance of life, numerical, 98-100.

Adaptation and aggressiveness of the organism, 80.

Additive law, the, with reference to alpha rays, 220.

Age of Earth, comparison of denudative and radioactive methods of

finding, 23-29.

Aletsch glacier, 286.

Allen, Grant, on colour of Alpine plants, 104.

Allen, H. Stanley, on photo-electricity, 203.

Alpha rays, nature of, 214; velocity of, 214; effects of, on

gases, 214; range of, in air, 215; visualised, 218; ionisation

curve of, 216; number of, from one gram of radium, 237; number of

ions made by, 237.

Alpine flowers, intensity of colour of, 102.

Alps, history of, 141; Tertiary denudation of, 148; depth of

sedimentary covering of, 148; evidence of high pressures and

temperatures in, 149; recent theories of formation of, 150 _et

seq._; upheaval of, 147; age of, 147; volcanic phenomena

attending elevation of, 147.

Andes, trough parallel to, 123; not volcanic in origin, 118.

Angle of friction on ice, 261-265, 281-283; on glass, 261-265.

Animate systems, dynamic conditions of, 67; and transfer of

energy, 71; and old age, 72; mechanical imitation of, 76, 77.

Animate and inanimate systems compared, 73-75.

Appalachian range, formation of, 120.

Arrhenius, on elevation of continents, 17.

Aryan Era of India, 136.

Asteroids, probable origin of, 175; discovery of, 175; dimensions

of, 176; orbits of, 176; Mars' moons derived from, 177.

B.

Babbage and Herschel, theory of mountain building, 123.

Babes (and Cornil), size of spores, 98.

Becker, G. F., age of Earth by sodium collection, 14; age of

minerals by lead ratio, 20.

Berthelot, law of maximum work, 62.

Bertrand, Marcel, section of Mont Blanc Massif, 154.

Beta rays, nature of, 246; accompanied by gamma rays, 247;

production of, by gamma rays, 247; as ionising agents, 249.

Biotite, containing haloes, 223; pleochroism of, 235; intensified

pleochroism in halo, 235.

Body and mind, as manifestations of progressiveness of the

organism, 86.

Boltwood, age of minerals by lead ratio, 20.

Bose, theory of latent image, 203.

Bragg and Kleeman, on path of the alpha ray, 215; stopping power,

219; laws affecting ionisation by alpha rays, 220; curve of

ionisation and structure of the halo, 232.

Brecciendecke, sheet of the, 154.

Brdche, sheet of the, 154.

Burrard and Hayden on the Himalaya, 138; sections of the

Himalaya, 139.

C.

Canals and "canali," 166; curvature of, and path of a satellite,

188 _et seq._; double and triple accounted for, 186, 187;

doubling of, 195; disappearance and reappearance of, 196-198;

photography of, 198; not due to cracks, 167; not due to rivers,

167; of Mars, double nature of, 166, 170; crossing dark regions

of planet's surface, 168; of Mars, Lowell's views on, 168 _et

seq._; shown on Lowell's map, investigation of, 192 _et seq._;

radiating, explanation of, 193, 194; number of, 194; developed by

secondary disturbances, 194; nodal development of, due to raised

surface features, 195.

Chamberlin and Salisbury, the Laramide range, 121.

Clarke, F. W., estimate of mass of sediments, 9; age of Earth by

sodium collection, 14; average composition of sedimentary and

igneous rocks, 42; on average composition of the crust, 126;

solvent denudation of the continents, 17, 40.

Claus, protoplasm the test of the cell, 67; abortion of useless

organs, 69.

Coefficient of friction, definition of, 262; deduction of, from

angle of friction, 263; abnormal values on ice, 261-265, 282; for

various substances, 265.

Continental areas, movements of, 144.

Cornil and Babes, size of spores, 98.

Croll, James, dawn of evolution, 301.

Crust of the Earth, average composition of, 126; depth of

softening in, 128.

Curie, definition of the, 256.

D.

Dana, on mountain building, 120.

Dawson, reduction of surface represented by Laramide range, 123.

Deccan traps, 137

_déferlement_, theory of, 155; explanation of, 155 _et seq._;

temperature involved in, 156.

Deimos, dimensions of, 177; orbit of, 577.

De Lapparent, exotic nature of the Préalpes, 150.

De Montessus and the association of earthquakes with

geosynclines, 142.

Denudation as affected by continental elevation, 17; factors

promoting, 30 _et seg._; relative activity in mountains and on

plains, 35-40; solvent, by the sea, 40; the sodium index of,

46-50; thickness of rock-layer removed from the land, 51.

De Quincy, System of the Heavens, 200.

Dewar, Sir James, latent image formed at low temperatures, 202.

Dixon, H. H., and AGnadance of Life, 60.

Double canals, formation by attraction of a satellite, 585-187.

Douglass, A. E., observations on Mars, 167.

Dravidian Era of India, 135.

E.

Earth, early history of, 3, 4; dimensions of, relative to surface

features, 117.

Earth's age determined by thickness of sediments, 5; determined

by mass of the sediments, 7; determined by sodium in the ocean,

12; determined by radioactive transformations, 19; significance

of, 2.

Earthquakes associated with geosynclincs, 142.

Efficiency, tendency to maximum, in organisms, 113, 114.

Elements, probable wide diffusion of rare, 230; rarity of

radioactive, 241.

Elster and Geitel, photo-electric activity and absorption, 207;

photo-electric properties of gelatin, 212; Emanation of radium,

therapeutic use of, 256-259; advantages of, in medicine, 256;

volume of, 257; how obtained, 257; use of, in needles, 258.

Equilibrium amount, meaning of, 254, 255.

Evolution and acceleration of activity, 79; of the universe not

eternal a pane ante, 298.

F.

Faraday and ionisation, 57.

Finality of progress a part, post, 289.

Flahault, experiments on colour of flowers, 108.

Fletcher, A. L., proportionality of thorium and uranium, 26,

G.

Galileo, discovery of Jupiter's moons, 162.

Gamma rays, nature of, 247: production of, by beta rays, 247; as

ionising agents, 249.

Geddes and Thomson, hunger and living matter, 71.

Geiger, range of alpha rays in air, 215; ionisation affected by

alpha rays in air, 216; on "scattering," 217; scattering and the

structure of the halo, 232.

Geikie, Sir A., uniformity in geological history, 15.

Geosynclines, 119; association with earthquakes and volcanoes,

142; of the tethys, 142; radioactive heat in, due to sediments,

130; temperature effects due to lateral compression of, 131.

Glacial epoch, phenomena of, 287.

Glacier motion, cause of. 285.

Glossopteris and Gangamopteris flora, 136.

Gondwanaland, 136.

Gradient of temperature in Earth's surface crust, 126.

H.

Haimanta period of India, 135.

Halley, Edmund, finding age by saltness of ocean, 13.

Hallwachs, photo-electric activity and absorption, 207.

Haloes, pleochroic, finding age of rocks by, 21; due to uranium

and thorium families, 227; radii of, 227; over-exposed and

underexposed, 228; intimate structure of, 229 _et seq._;

artificial, 229; tubular, in mica, 230; extreme age of, 231;

effect of nucleus on structure of, 232; inference from spherical

form of, in crystals, 233; structure of, unaffected by cleavage,

235; origin of the name "pleochroic,"235; colouration due to

iron, 235; colouration not due to helium, 236; age Of, 236; slow

formation of, 237, 238; number of rays required to build, 237;

and age of the Earth, 238-241.

Hayden, H.H., geology of the Himalaya, 134, 138, 139.

Heat-tendency of the universe, 62.

Heat emission from the Earth's surface, 126; from average igneous

rock due to radioactivity, 126.

Helium and the alpha ray, 214, 222; colouration of halo not due

to, 236.

Hering, E., and physiological or unconscious memory, 111.

Herschel and Babbage theory of mountain building, 123.

Herschel, Sir W., on galaxy of milky way, 293.

Hertz, negative electrification discharged by light, 204.

Himalaya, geological history of, 134-139.

Hobbs, on association of earthquakes and geosynclines, 143.

Holmes, A., original lead in minerals, 20; age of Devonian, 21.

Horst concerned in Alpine _déferlement_, objections to, 156.

Hyperion, dimensions of, 177.

I.

Ice, melting of, by pressure, 267 _et seq._; expansion of water

in becoming, 267; lowering of melting-point by pressure, 267;

fall of temperature under pressure, 268 _et seq._; viscosity of,

284.

Igneous rocks, average composition of, 43.

Inanimate actions, dynamic conditions of, 61.

Inanimate systems, secondary effects in, 63-65; transfer of

energy into, 66.

Indian geology, equivalent nomenclature of, 139.

Initial recombination of ions due to alpha rays, 221, 222, 231;

and structure of the halo, 231.

Insect life in the higher Alps, 104, 105; destruction of, on the

Alpine snows, 106.

Ionisation by alpha ray, density of, 221; importance in chemical

actions, 250; in living cell, 250.

Ions, number of, produced by an alpha ray, 237.

Isostasy, 53; and preservation of continents, 53.

Ivy, inconspicuous blossoms of, 107; delay in ripening seed,

107.

K.

Kant and Laplace, material hypothesis of, does not account for

the past, 290.

Kelvin, Lord, experiment on effects of pressure on ice, 268-270.

Kleeman and Bragg. See Bragg.

Klopstock introduces skating into Germany, 273.

L.

Lakes, cause of blue colour of, 55.

Land, movements of the, 53, 54.

Laukester, Ray, the soma and reproductive cells, 85.

Lapworth, structure of the Scottish Highlauds, 153.

Latent heat of water, 266.

Latent image, formed at low temperatures, 202; Bose's theory of,

203; photo-electric theory of, 204, 209 _et seq._

Least action, law of, 66.

Lembert and Richards, atomic weight of lead, 27.

Length of life dependent on conditions of structural development,

93; dependent on rate of reproduction, 94.

Life-curves of organisms having different activities, 92.

Life, length of, 91.

Life waves of a cerial, 95; of Ausaeba, 87; of a species, 90.

Light, effects of, in discharging negative electrification, 204;

chemical effects of, 205; experiment showing effect of, in

discharging electrified body, 205.

Lindemann, Dr., duration of solar heat, 29.

Lowell, Percival, observations on Mars, 167 _et seq._; map of

Mars, reliability of, 198.

Lucretius, birth-time of the world, 1.

Lugeon, formation of the Préalpes, 171; sections in the Alps,

154.

Lyell, uniformity in geological history, 15.

M.

Magee, relative areas of deposition and denudation, 16.

Mars, climate of, 170; position in solar system, 174, 175;

dimensions of satellites of, 177; snow on, 169; water on, 169;

clouds on, 169; atmosphere of, 170; melting of snow on, 170;

dimensions of canals, 171; signal on, 172; times of opposition,

164; orbit of, 165; distance from the Earth, 165; eccentricity of

his orbit, 165; observations of, by Schiaparelli, 165, 166;

Lowell's observations on, 167 _et seq._

Maxwell, Clerk, changes made under constraints, 65; on

conservation of energy, 61.

M'Connel, J. C., viscosity and rigidity of ice, 284.

Memory, physiological, 111, 112.

Metamorphism, thermal, in Alpine rocks, 132, 149

Millicurie, definition of, 256.

Molasse, accumulations of, 148.

Morin, coefficients of friction, 265.

Morphy, H., experiments on coefficient of friction of ice, 281.

Mountain-building and the geosynclines, 119-121; conditioned by

radioactive energy, 125; energy for, due to gravitation, 122;

reduction of surface attending, 123; depression attending, 123;

instability due to thermal effects of compression, 132; igneous

phenomena attending, 132; rhythmic character of, accounted for,

133; movements confined to upper crust, 122; movements due to

compressive stresses in crust, 122; movements, rhythmic character

of, 121.

Mountain ranges built of sedimentary materials, 118.

Müller, J., coefficient of friction of skate on ice, 265, 274.

Muth deposits of India, 135.

N.

Newton, Professor, of Yale, on origin of Mars' satellites, 177.

Nucleus, dimensions of, 237; amount of radium in, 238.

Nummulitic beds of Himalaya, 138.

O.

Ocean, amount of rock salt in, 50; cause of black colour of, 55;

estimated mass of sediments in, 48; increase of bulk due to

solvent denudation, 52; its saltness due to denudation, 41.

Old age and death, 82-85; not at variance with progressive

activity, 83.

Organic systems, origin of, 78.

Organic vibrations, 86 _et seq._

Organism and accelerative absorption of energy, 79; and economy,

109-111; and periodic rigour of the environment, 94,95.

Organism and sleep, 95; ultimate explanation of rythmic events

in, 96, 97; law of action of, 68 _et seq._; periodicity of; and

law of progressive activity, 82 _et seq._

P.

Penjal traps, 135.

Pepys and skating, 273.

Perry, coefficient of friction of greased surfaces, 265.

Phobos, dimensions of, 177; orbit of, 177.

Photoelectric activity and absorption, 207; persists at low

temperatures, 208, 209; not affected by solution, 213.

Photo-electric experiment, 205; sensitiveness of the hands, 207;

theory of latent image, 204, 209 _et seq._

Photographic reversal, experiments on, by Wood, 211; theory of,

210.

Piazzi, discovery of first Asteroid, 175.

Pickering, W. H., observations on Mars, 167.

Planet, slowing of axial rotation of, 189.

Plant, expectant attitude of, 109.

Pleochroic haloes, measurements of, 224; theory of, 224 _et

seq._; true form of, 226; radius of, and the additive law, 225;

absence of actinium haloes, 225; see _also_ Haloes; mode of

occurrence of, 223 _et seq._

Poole, J. H. J., proportionality of thorium and uranium, 26.

Poulton, uniformity of past climate, 17.

Pratt, Archdeacon, and isostasy, 53.

Préalpes, exotic nature of, 150, 151.

Prematerial universe, nature of a, 297, 300.

Prestwich and thickness of rigid crust, 128; history of the

Pyrenees, 140.

Primitive organisms, interference of, 89; life-curves of, 88.

Proctor and orbits of Asteroids, 176.

Protoplasm, encystment of, 68.

Purana Era of India, 134.

Pyrenees, history of, 140.

R.

Radioactive elements concerned in mountain building, 125.

Radioactive layer, failure to account for deep-seated

temperatures, 127; assumed thickness of, 128; temperature at base

of, due to radioactivity, 129; in the upper crust of the Earth,

125; thickness of, 126-128.

Radioactive treatment, physical basis of, 251.

Radioactivity and heat emission from average igneous rock, 126;

rarity of, established by haloes, 241, 243.

Radium, chemical nature and transmutation of, 244-245; emanation

of, 245; rays from, 253, 254; table of family of, 253; period of,

253; small therapeutic value of, 254.

Radium C, therapeutic value of, 254; rays from. 254; generation

of, 254.

Rationality, conditions for development of, 163.

Rays, similarity in nature of gamma, X, and light rays, 248;

effects on living cell, 251; penetration of, 251.

Reade, T. Mellard, finding age of ocean by calcium sulphate, 13.

Recumbent folds, formation of, 155 _et seq._

Regelation, 284; affecting glacier motion, 285.

Reversal, photographic, explanation of, 211.

Richards and Lembert, atomic weight of lead, 27.

Richter, Jean Paul, Dream of the Universe, 200.

Rock salt in the ocean, amount of, 13.

Rocks, average composition of, 43; radioactive heat from, 126;

rate of solution of, 36.

Russell, I. C., river supply of sediments, 10.

Rutherford, Sir E., determination of age of minerals, 19, 20; age

of rocks by haloes, 22; derivation of actinium, 226; artificial

halo, 229; number of alpha rays from one gram of radium, 237.

S.

Salt range deposits of India, 134. 135.

Saltness of the ocean due to denudation, 41-46.

Salisbury (and Chamberlin), the Larimide range, 121.

Salmon, Rev. George, on creation, 301.

Satellite, velocity of, in its orbit, 191; method of finding path

of, over a rotating primary, 189 _et seq._; direct and

retrograde, 178; ultimate end of, 178; path of, when falling into

primary, 179; effect of Mars' atmosphere on infalling satellite,

179; stability of close to primary, 180; effects of, on crust of

primary, 180 _et seq._

Schiaparelli, observations on Mars, 165 166.

Schmidt, C., original depth of Alpine layer, 131-148; structure

of the Alps, 152.

Schmidt, G. C., on photo-electricity, 207, 208; effect of

solution on photo-electric activity, 213.

Schuchert, C., average area of N. America during geological time,

16.

Sedimentary rocks, average composition of, 43; mass of,

determined by sodium index, 47.

Sedimentation a convection of energy, 133.

Sediments, average river supply of, 11; on ocean floor, mass of,

48; average thickness of, 49; precipitation of, by dissolved

salts, 56-58; radioactivity of 130; radioactive heat of,

influential in mountain building, 130, 131; rate of collecting,

7; determination of mass of, 8; river supply of, 10; total

thickness of, 6.

Semper, energy absorption of vegetable and animal systems, 78.

Sensitisers, effects of low temperature on, 210.

Simplon, radioactive temperature in rocks of, before denudation,

132.

Skates, early forms of, 273; principles of construction of, 273

_et seq._; action of, on ice, 276; bite of, 278-280.

Skating not dependent on smoothness of ice, 260; history of,

273.

Skating only possible on very few substances, 279.

Soddy, F., on isotopes, 24.

Sodium, deficiency of, in sediments, 44; discharge of rivers,

14.

Soils, formation of, 37-39; surface area exposed in, 39.

Sollas, W. J., age of Earth by sodium in ocean, 14; thickness of

sediments, 6.

Spencer, on division of protoplasm, 67.

Spores, number of molecules in, 97.

Stevenson, Dr. Walter C., and technique of radioactive treatment,

259.

Stoletow, photo-electric activity anal absorption, 207.

Stopping power of substances with reference to alpha rays, 219.

Struggle for existence, dynamic basis of, 80.

Strutt, Prof. the Hon. R. J., age of geological periods, 20;

radioactivity of zircon, 223.

Sub-Apennine series of Italy, 148.

Suess, nature of earthquakes. 143.

Survival of the fittest and the organic law, 80.

T.

Talchir boulder-bed, 136.

Temperature gradient in Earth's crust, 126.

Termier, section of the Pelvoux Massif, 254.

Tethys, early extent of, 135-137; geosynclines of, 142.

Thermal metamorphism in Alpine rocks, 132, 149.

Thomson, James, prediction of melting of ice by pressure, 267.

Thorium and uranium, proportionality of, in older rocks, 26.

Triple canals, formation of, by attraction of a satellite, 187.

Tyndall, colour of ocean water, 55.

U.

Uniformitarian view of geological history, 15-18.

Universe, simultaneity of the, 293-295.

Uranium-radium family of elements, table of, 253.

V.

Val d'Hérens, earth pillars of, 33.

Van Tillo, nature of continental rock covering, 9.

Vegetable and animal systems, relative absorption of energy of,

78.

Vegetative organs, struggle between, 105, 106.

Volcanoes and mountain ranges, 118; associated with geosynclines,

142; Oligocene and Miocene of Europe, 147.

W.

Weinschenk and thermal metamorphism, 132,

149.

Weismaun, encystment of protoplasm, 68; length of life and

somatic cells, 96; origin of death, 83; tendency to early

reproductiveness, 98.

Wilson, C. T. R., visualised alpha rays, 218.

Winchell, progressive changes of matter not eternal, 302.

Wood, R. W., on photographic reversal, 211.

Z.

Zircon, radioactivity of, 223; as nucleus of halo, 223.

*** END OF THE PROJECT GUTENBERG EBOOK THE BIRTH-TIME OF THE WORLD AND OTHER SCIENTIFIC ESSAYS ***

Updated editions will replace the previous one—the old editions will be renamed.

Creating the works from print editions not protected by U.S. copyright law means that no one owns a United States copyright in these works, so the Foundation (and you!) can copy and distribute it in the United States without permission and without paying copyright royalties. Special rules, set forth in the General Terms of Use part of this license, apply to copying and distributing Project Gutenberg™ electronic works to protect the PROJECT GUTENBERG™ concept and trademark. Project Gutenberg is a registered trademark, and may not be used if you charge for an eBook, except by following the terms of the trademark license, including paying royalties for use of the Project Gutenberg trademark. If you do not charge anything for copies of this eBook, complying with the trademark license is very easy. You may use this eBook for nearly any purpose such as creation of derivative works, reports, performances and research. Project Gutenberg eBooks may be modified and printed and given away—you may do practically ANYTHING in the United States with eBooks not protected by U.S. copyright law. Redistribution is subject to the trademark license, especially commercial redistribution.

START: FULL LICENSE

THE FULL PROJECT GUTENBERG LICENSE

PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK

To protect the Project Gutenberg™ mission of promoting the free distribution of electronic works, by using or distributing this work (or any other work associated in any way with the phrase “Project Gutenberg”), you agree to comply with all the terms of the Full Project Gutenberg™ License available with this file or online at www.gutenberg.org/license.

Section 1. General Terms of Use and Redistributing Project Gutenberg™ electronic works

1.A. By reading or using any part of this Project Gutenberg™ electronic work, you indicate that you have read, understand, agree to and accept all the terms of this license and intellectual property (trademark/copyright) agreement. If you do not agree to abide by all the terms of this agreement, you must cease using and return or destroy all copies of Project Gutenberg™ electronic works in your possession. If you paid a fee for obtaining a copy of or access to a Project Gutenberg™ electronic work and you do not agree to be bound by the terms of this agreement, you may obtain a refund from the person or entity to whom you paid the fee as set forth in paragraph 1.E.8.

1.B. “Project Gutenberg” is a registered trademark. It may only be used on or associated in any way with an electronic work by people who agree to be bound by the terms of this agreement. There are a few things that you can do with most Project Gutenberg™ electronic works even without complying with the full terms of this agreement. See paragraph 1.C below. There are a lot of things you can do with Project Gutenberg™ electronic works if you follow the terms of this agreement and help preserve free future access to Project Gutenberg™ electronic works. See paragraph 1.E below.

1.C. The Project Gutenberg Literary Archive Foundation (“the Foundation” or PGLAF), owns a compilation copyright in the collection of Project Gutenberg™ electronic works. Nearly all the individual works in the collection are in the public domain in the United States. If an individual work is unprotected by copyright law in the United States and you are located in the United States, we do not claim a right to prevent you from copying, distributing, performing, displaying or creating derivative works based on the work as long as all references to Project Gutenberg are removed. Of course, we hope that you will support the Project Gutenberg™ mission of promoting free access to electronic works by freely sharing Project Gutenberg™ works in compliance with the terms of this agreement for keeping the Project Gutenberg™ name associated with the work. You can easily comply with the terms of this agreement by keeping this work in the same format with its attached full Project Gutenberg™ License when you share it without charge with others.

1.D. The copyright laws of the place where you are located also govern what you can do with this work. Copyright laws in most countries are in a constant state of change. If you are outside the United States, check the laws of your country in addition to the terms of this agreement before downloading, copying, displaying, performing, distributing or creating derivative works based on this work or any other Project Gutenberg™ work. The Foundation makes no representations concerning the copyright status of any work in any country other than the United States.

1.E. Unless you have removed all references to Project Gutenberg:

1.E.1. The following sentence, with active links to, or other immediate access to, the full Project Gutenberg™ License must appear prominently whenever any copy of a Project Gutenberg™ work (any work on which the phrase “Project Gutenberg” appears, or with which the phrase “Project Gutenberg” is associated) is accessed, displayed, performed, viewed, copied or distributed:

This eBook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.

1.E.2. If an individual Project Gutenberg™ electronic work is derived from texts not protected by U.S. copyright law (does not contain a notice indicating that it is posted with permission of the copyright holder), the work can be copied and distributed to anyone in the United States without paying any fees or charges. If you are redistributing or providing access to a work with the phrase “Project Gutenberg” associated with or appearing on the work, you must comply either with the requirements of paragraphs 1.E.1 through 1.E.7 or obtain permission for the use of the work and the Project Gutenberg™ trademark as set forth in paragraphs 1.E.8 or 1.E.9.

1.E.3. If an individual Project Gutenberg™ electronic work is posted with the permission of the copyright holder, your use and distribution must comply with both paragraphs 1.E.1 through 1.E.7 and any additional terms imposed by the copyright holder. Additional terms will be linked to the Project Gutenberg™ License for all works posted with the permission of the copyright holder found at the beginning of this work.

1.E.4. Do not unlink or detach or remove the full Project Gutenberg™ License terms from this work, or any files containing a part of this work or any other work associated with Project Gutenberg™.

1.E.5. Do not copy, display, perform, distribute or redistribute this electronic work, or any part of this electronic work, without prominently displaying the sentence set forth in paragraph 1.E.1 with active links or immediate access to the full terms of the Project Gutenberg™ License.

1.E.6. You may convert to and distribute this work in any binary, compressed, marked up, nonproprietary or proprietary form, including any word processing or hypertext form. However, if you provide access to or distribute copies of a Project Gutenberg™ work in a format other than “Plain Vanilla ASCII” or other format used in the official version posted on the official Project Gutenberg™ website (www.gutenberg.org), you must, at no additional cost, fee or expense to the user, provide a copy, a means of exporting a copy, or a means of obtaining a copy upon request, of the work in its original “Plain Vanilla ASCII” or other form. Any alternate format must include the full Project Gutenberg™ License as specified in paragraph 1.E.1.

1.E.7. Do not charge a fee for access to, viewing, displaying, performing, copying or distributing any Project Gutenberg™ works unless you comply with paragraph 1.E.8 or 1.E.9.

1.E.8. You may charge a reasonable fee for copies of or providing access to or distributing Project Gutenberg™ electronic works provided that:

- • You pay a royalty fee of 20% of the gross profits you derive from the use of Project Gutenberg™ works calculated using the method you already use to calculate your applicable taxes. The fee is owed to the owner of the Project Gutenberg™ trademark, but he has agreed to donate royalties under this paragraph to the Project Gutenberg Literary Archive Foundation. Royalty payments must be paid within 60 days following each date on which you prepare (or are legally required to prepare) your periodic tax returns. Royalty payments should be clearly marked as such and sent to the Project Gutenberg Literary Archive Foundation at the address specified in Section 4, “Information about donations to the Project Gutenberg Literary Archive Foundation.”

- • You provide a full refund of any money paid by a user who notifies you in writing (or by e-mail) within 30 days of receipt that s/he does not agree to the terms of the full Project Gutenberg™ License. You must require such a user to return or destroy all copies of the works possessed in a physical medium and discontinue all use of and all access to other copies of Project Gutenberg™ works.

- • You provide, in accordance with paragraph 1.F.3, a full refund of any money paid for a work or a replacement copy, if a defect in the electronic work is discovered and reported to you within 90 days of receipt of the work.

- • You comply with all other terms of this agreement for free distribution of Project Gutenberg™ works.

1.E.9. If you wish to charge a fee or distribute a Project Gutenberg™ electronic work or group of works on different terms than are set forth in this agreement, you must obtain permission in writing from the Project Gutenberg Literary Archive Foundation, the manager of the Project Gutenberg™ trademark. Contact the Foundation as set forth in Section 3 below.

1.F.

1.F.1. Project Gutenberg volunteers and employees expend considerable effort to identify, do copyright research on, transcribe and proofread works not protected by U.S. copyright law in creating the Project Gutenberg™ collection. Despite these efforts, Project Gutenberg™ electronic works, and the medium on which they may be stored, may contain “Defects,” such as, but not limited to, incomplete, inaccurate or corrupt data, transcription errors, a copyright or other intellectual property infringement, a defective or damaged disk or other medium, a computer virus, or computer codes that damage or cannot be read by your equipment.

1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the “Right of Replacement or Refund” described in paragraph 1.F.3, the Project Gutenberg Literary Archive Foundation, the owner of the Project Gutenberg™ trademark, and any other party distributing a Project Gutenberg™ electronic work under this agreement, disclaim all liability to you for damages, costs and expenses, including legal fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH DAMAGE.

1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a defect in this electronic work within 90 days of receiving it, you can receive a refund of the money (if any) you paid for it by sending a written explanation to the person you received the work from. If you received the work on a physical medium, you must return the medium with your written explanation. The person or entity that provided you with the defective work may elect to provide a replacement copy in lieu of a refund. If you received the work electronically, the person or entity providing it to you may choose to give you a second opportunity to receive the work electronically in lieu of a refund. If the second copy is also defective, you may demand a refund in writing without further opportunities to fix the problem.

1.F.4. Except for the limited right of replacement or refund set forth in paragraph 1.F.3, this work is provided to you ‘AS-IS’, WITH NO OTHER WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PURPOSE.

1.F.5. Some states do not allow disclaimers of certain implied warranties or the exclusion or limitation of certain types of damages. If any disclaimer or limitation set forth in this agreement violates the law of the state applicable to this agreement, the agreement shall be interpreted to make the maximum disclaimer or limitation permitted by the applicable state law. The invalidity or unenforceability of any provision of this agreement shall not void the remaining provisions.

1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the trademark owner, any agent or employee of the Foundation, anyone providing copies of Project Gutenberg™ electronic works in accordance with this agreement, and any volunteers associated with the production, promotion and distribution of Project Gutenberg™ electronic works, harmless from all liability, costs and expenses, including legal fees, that arise directly or indirectly from any of the following which you do or cause to occur: (a) distribution of this or any Project Gutenberg™ work, (b) alteration, modification, or additions or deletions to any Project Gutenberg™ work, and (c) any Defect you cause.

Section 2. Information about the Mission of Project Gutenberg™

Project Gutenberg™ is synonymous with the free distribution of electronic works in formats readable by the widest variety of computers including obsolete, old, middle-aged and new computers. It exists because of the efforts of hundreds of volunteers and donations from people in all walks of life.

Volunteers and financial support to provide volunteers with the assistance they need are critical to reaching Project Gutenberg™’s goals and ensuring that the Project Gutenberg™ collection will remain freely available for generations to come. In 2001, the Project Gutenberg Literary Archive Foundation was created to provide a secure and permanent future for Project Gutenberg™ and future generations. To learn more about the Project Gutenberg Literary Archive Foundation and how your efforts and donations can help, see Sections 3 and 4 and the Foundation information page at www.gutenberg.org.

Section 3. Information about the Project Gutenberg Literary Archive Foundation

The Project Gutenberg Literary Archive Foundation is a non-profit 501(c)(3) educational corporation organized under the laws of the state of Mississippi and granted tax exempt status by the Internal Revenue Service. The Foundation’s EIN or federal tax identification number is 64-6221541. Contributions to the Project Gutenberg Literary Archive Foundation are tax deductible to the full extent permitted by U.S. federal laws and your state’s laws.

The Foundation’s business office is located at 809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887. Email contact links and up to date contact information can be found at the Foundation’s website and official page at www.gutenberg.org/contact

Section 4. Information about Donations to the Project Gutenberg Literary Archive Foundation

Project Gutenberg™ depends upon and cannot survive without widespread public support and donations to carry out its mission of increasing the number of public domain and licensed works that can be freely distributed in machine-readable form accessible by the widest array of equipment including outdated equipment. Many small donations ($1 to $5,000) are particularly important to maintaining tax exempt status with the IRS.

The Foundation is committed to complying with the laws regulating charities and charitable donations in all 50 states of the United States. Compliance requirements are not uniform and it takes a considerable effort, much paperwork and many fees to meet and keep up with these requirements. We do not solicit donations in locations where we have not received written confirmation of compliance. To SEND DONATIONS or determine the status of compliance for any particular state visit www.gutenberg.org/donate.

While we cannot and do not solicit contributions from states where we have not met the solicitation requirements, we know of no prohibition against accepting unsolicited donations from donors in such states who approach us with offers to donate.

International donations are gratefully accepted, but we cannot make any statements concerning tax treatment of donations received from outside the United States. U.S. laws alone swamp our small staff.

Please check the Project Gutenberg web pages for current donation methods and addresses. Donations are accepted in a number of other ways including checks, online payments and credit card donations. To donate, please visit: www.gutenberg.org/donate.

Section 5. General Information About Project Gutenberg™ electronic works

Professor Michael S. Hart was the originator of the Project Gutenberg™ concept of a library of electronic works that could be freely shared with anyone. For forty years, he produced and distributed Project Gutenberg™ eBooks with only a loose network of volunteer support.

Project Gutenberg™ eBooks are often created from several printed editions, all of which are confirmed as not protected by copyright in the U.S. unless a copyright notice is included. Thus, we do not necessarily keep eBooks in compliance with any particular paper edition.

Most people start at our website which has the main PG search facility: www.gutenberg.org.

This website includes information about Project Gutenberg™, including how to make donations to the Project Gutenberg Literary Archive Foundation, how to help produce our new eBooks, and how to subscribe to our email newsletter to hear about new eBooks.

Table of Contents

THE FULL PROJECT GUTENBERG LICENSE