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diff --git a/16614.txt b/16614.txt new file mode 100644 index 0000000..6c22bc8 --- /dev/null +++ b/16614.txt @@ -0,0 +1,10229 @@ +The Project Gutenberg EBook of The Birth-Time of the World and Other +Scientific Essays, by J. (John) Joly + +This eBook is for the use of anyone anywhere 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 + + +Title: The Birth-Time of the World and Other Scientific Essays + +Author: J. (John) Joly + +Release Date: August 28, 2005 [EBook #16614] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK THE BIRTH-TIME OF THE WORLD *** + + + + +Produced by Hugh Rance + + + + + +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 + + +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." DUeSSISTOCK; 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 +HOeHBALM. 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 + +Archaean - - ? + +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 1016 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 archaean 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 1018 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 +archaean 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. +Archaean - 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 archaean 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'Electricite_, 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 _debris_ 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'Herens +(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'Herens +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 _debris_ 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 (SiO2) - 59.99 58.51 +Alumina (Al2O3) - 15.04 13.07 +Ferric oxide (F2O3) - 2.59 3.40 +Ferrous oxide (FeO) - 3.34 2.00 +Magnesia (MgO) - 3.89 2.52 +Lime (CaO) - 4.81 5.42 +Soda (Na2O) - 3.41 1.12 +Potash (K2O) - 2.95 2.80 +Water (H2O) - 1.92 4.28 +Carbon dioxide (CO2) - -- 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 1016 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 1016 +tonnes. + +Now from the mean chemical composition of the secondary rocks we +calculate that the mass of sediments as above determined contains +0.72 x1016 tonnes of the sodium oxide, Na2O. 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 1016 tonnes. Hence +between the estimated sediments and the waters of the ocean we +can account for 2.82 x 1016 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 1012 tonnes, say. + +Keeping the figures to round numbers we find that this amount of +sodium involves the denudation of about 80 x 1016 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 1016 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 1016 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 1016 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 1016 +tonnes. The dissolved salts in it constitute 3.4 per cent. of its +mass; or, rather more than 5 x 1016 tonnes. The limestones on the +land and the salts in the sea water together make up about 8 x +1016 tonnes. If we, now, deduct this from the total of 27 x 1016 +tonnes, we find that about 19 x 1016 tonnes must exist as +precipitated matter on the floor of the ocean. + +The area of the ocean is 367 x 1012 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 Mecanique 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 aether; 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 aesthetic 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 +aesthetic 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 aesthetic 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 aesthetic 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 Toedi from the Fridolinshuete 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 aesthetic 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 deg. >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 deg. 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 deg. 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, t1 deg.. 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 t2 deg., by the proportion t1 deg. : t2 deg. :: +12 deg. : 22 deg. 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 deg. to 1000 deg. 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, _Congres Geol. 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 Archaean 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 Palaeozoic 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 - Archaean. +Daling Series - Archaean. + +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 _debris_ 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 _debris_, 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 deg. C. if the +gradients were such as obtain in mountain regions generally; and +600 deg. 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. _Congres Geol._, 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 Prealpes, 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 +Prealpes are, in fact, mountains without local roots. + +In this last-named essential feature, the Prealpes 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 Prealpes. With Lugeon[2] we may see in the phenomenon of +the formation of the Prealpes 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, _Traite de Geologie_, p. 1,785. + +[2] Lugeon, _Bulletin Soc. Geol. 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 +Prealpes 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 Prealpes, +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 Breche (_Byecciendecke_) falls short, in its northerly +extension, of the underlying fold, which extends to form the +Prealpes. + +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 Breche 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. Geol. Internat._, 1900, Guide Geol., +xiii. a, p. 41. + +[2] Lugeon, _loc. cit._, p. 773. + +[3] De Lapparent, _Traite de Geol._, p. 1,773. + +154 + +the recumbent folds and the peculiar phenomena of increasing +overlap, or _deferlement_, 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 _deferlement_ 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 deg. 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 deg. or +600 deg. . 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 _deferlement_, 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 +_deferlement_ 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 _deferlement_ 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 71/2 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 21/2 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 deg. 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 deg. C, + +Sir James Dewar's actual measilrements afforded twenty per cent. +of the normal photographic effect at -180 deg. C. and ten per cent. +at the temperature of -252.5 deg. 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 deg. 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 deg. 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, +prima 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 1010, 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 105 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 _debris_--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 1/2 element is transformed. + +URANIUM 1 & 2 { a 6 } x 109 years. + +URANIUM X { a ss } 24.6 days. + +IONIUM { a 8 } x 104 years. + +RADIUM { a ss } 2 x 102 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 121/2 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 61/2 +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 121/2 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 deg. 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 deg. C. It is about +10 deg. 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 131/2, 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 deg.. + +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 deg. 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 deg. C. at 10 deg. C. + + Angle. Coeff. Angle. Coeff. Angle. Coeff +Aluminium 2.55 121/2 deg. 0.22 12 deg. 0.21 131/2 deg. 0.24 +Same 155 121/2 deg. 0.22 6 deg. 0.11 7 deg. 0.12 +Brass 6.5 121/2 deg. 0.22 10 deg. 0.17 101/2 deg. 0.18 +Same 107 121/2 deg. 0.22 5 deg. 0.09 6 deg. 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. Mueller) - - - 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 deg. 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 deg. 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 deg. 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 deg. C. or 32 deg. 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 deg. C., but at -7.5 deg. C. or about +18 deg. 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 deg. C., _i.e._ at 0.0075 deg. 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 deg. 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 deg. C. to start with. Then +suppose we apply, say, one thousand atmospheres pressure. The +melting point of the ice is lowered to -7.5 deg. C. That is, it will +require a temperature so low as -7.5 deg. 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 deg. C., but a higher temperature, +_i.e._ 0 deg. C. In other words, it is 7.5 deg. 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 deg. 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 deg. 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 deg. 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 deg. C. + +269 + +and at the normal pressure. Water at -7.5 deg. 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 deg. 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 deg. 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 deg.. 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 deg. C. Suppose we apply such a pressure to this +ice as will confer a melting point of -2 deg. C. on it. Obviously, +there will be no melting. For why should ice which is at -3 deg. C. +melt when its melting point is -2 deg. 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. Mueller 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 deg.. 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 deg. 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 deg. 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 deg.+-30' -5.65 deg. C. +10.39 -5.65 deg. +11.96 -5.75 deg. +12.74 -5.60 deg. +13.53 -5.65 deg. +14.31 -5.65 deg. +15.10 grams. 0.17+-.01 9 deg..30'+-30' -5.60 deg. +16.67 -5.55 deg. +19.81 -5.60 deg. +24.52 -5.60 deg. +5.68 grams. 0.36+-.01 20 deg.+-30' -5.60 deg. + +"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 deg. 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 _a 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 + +_deferlement_, 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 Prealpes, 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 _deferlement_, 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 Prealpes, 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. + +Mueller, 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. + +Prealpes, 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'Herens, 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 of The Birth-Time of the World and Other +Scientific Essays, by J. (John) Joly + +*** END OF THIS PROJECT GUTENBERG EBOOK THE BIRTH-TIME OF THE WORLD *** + +***** This file should be named 16614.txt or 16614.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/1/6/6/1/16614/ + +Produced by Hugh Rance + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions 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. 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