,,the ,,birth-,,time ,,of ,,the ,,world ,,and ,,other ,,scientific ,,essays by ,j4 ,,joly1 ,m4,a41 ,sc4,d41 ,f4,r4,s41 ,,professor ,,of ,,geology ,,and ,,mineralogy ,,in ,,the ,,university ,,of ,,dublin ,e4 ,p4 ,,dutton ,,and ,,company #fha ,,fifth ,,avenue ,,new ,,york ,cover ,title page ,,contents ,,page ,i4 ,,the ,,birth-,,time ,,of ,,the ,,world - - - - - - - - - - - #a ,,ii4 ,,denudation - - - - - - - - - - - - - - - - - - #cj ,,iii4 ,,the ,,abundance ,,of ,,life - - - - - - - - - - - - #fj ,,iv4 ,,the ,,bright ,,colours ,,of ,,alpine ,,flowers - - - - - #ajb ,v4 ,,mountain ,,genesis - - - - - - - - - - - - - - - #aaf ,,vi4 ,,alpine ,,structure - - - - - - - - - - - - - - - #adf ,,vii4 ,,other ,,minds ,,than ,,ours - - - - - - - - - - - - #afb ,,viii4 ,,the ,,latent ,,image - - - - - - - - - - - - - - #bjb ,,ix4 ,,pleochroic ,,haloes - - - - - - - - - - - - - - #bad ,x4 ,,the ,,use ,,of ,,radium ,,in ,,medicine - - - - - - - - - #bdd ,,xi4 ,,skating - - - - - - - - - - - - - - - - - - - #bfj ,,xii4 ,a ,,speculation ,,as ,,to ,a ,,pre-,,material ,,universe - #bhh ,,list ,,of ,,illustrations ,,plate ,i4 ,,lake ,,of ,,lucerne1 ,,looking ,,west ,,from ,,brunnen - ,frontispiece ,,plate ,,ii4 ,,uplifted ,,from ,,the ,,seas4 ,,cliffs ,,of ,,the ,,titlis1 ,,switzerland - to face p4 #d ,,plate ,,iii4 ,,an ,,alpine ,,torrent ,,at ,,work--,,val ,d',,herens1 ,,switzerland - to face p4 #ca ,,plate ,,iv4 ,,earth ,,pillars--,,val ,d',,herens - to face p4 #cd ,,plate ,v4 ,,scenes ,,of ,,desolation4 ,,the ,,weisshorn ,,seen ,,from ,,bella ,,tola1 ,,switzerland - to face p4 #dj ,,plate ,,vi4 ,,alluvial ,,cone--,,nicolai ,,thal1 ,,switzerland4 ,,moraine ,,on ,,aletsch ,,glacier ,,switzerland - to face p4 #ej ,,plate ,,vii4 ,,in ,,the ,,region ,,of ,,the ,,croci2 ,,dolomites4 ,,the ,,rothwand ,,seen ,,from ,,monte ,,piano - to face p4 #fj ,,plate ,,viii4 ,,firs ,,assailing ,,the ,,heights ,,of ,,the ,,maderaner ,,thal1 ,,switzerland - to face p4 #gc ,,plate ,,ix4 ,,life ,,near ,,the ,,snow ,,line2 ,,the ,,bog-,,cotton ,,in ,,possession4 ,,near ,,the ,,tschingel ,,pass1 ,,switzerland - to face p4 #hj ,,plate ,x4 ,,the ,,joy ,,of ,,life4 ,,the ,,ampezzo ,,thal2 ,,dolomites - to face p4 #ic ,,plate ,,xi4 ,,pines ,,solemnly ,,quiet4 ,d,,ssistock2 ,,maderaner ,,thal - to face p4 #ajj ,,plate ,,xii4 ,,alpine ,,flowers ,,in ,,the ,,valleys - to face p4 #aje ,,plate ,,xiii4 ,,alpine ,,flowers ,,on ,,the ,,heights - to face p4 #ajf ,,plate ,,xiv4 ,,mountain ,,solitudes2 ,,val ,,de ,,zinal4 ,,from ,,left ,,to ,,right ,,rothhorn2 ,,besso2 ,,obergabelhorn2 ,,matterhorn2 ,,pic ,,de ,,zinal 7,,through ,,cloud72 ,,dent ,,blanche - to face p4 #aaf ix ,,plate ,,xv4 ,,sector ,,of ,,the ,,earth ,,rise ,,of ,,isogeotherms ,,into ,a ,,deposit ,,evolving ,,radioactive ,,heat - to face p4 #aah ,,plate ,,xvi4 ,,the ,,mountains ,,come ,,and ,,go4 ,,the ,,dent ,,blanche ,,seen ,,from ,,the ,,sasseneire - to face p4 #acc ,,plate ,,xvii4 ,,diagrammatic ,,sections ,,of ,,the ,,himalaya - to face p4 #adj ,,plate ,,xviii4 ,,residues ,,of ,,denudation4 ,,the ,,matterhorn ,,seen ,,from ,,the ,,summit ,,of ,,the ,,zinal ,,rothhorn - to face p4 #adh ,,plate ,,xix4 ,,the ,,folded ,,rocks ,,of ,,the ,,matterhorn1 ,,seen ,,from ,,near ,h,,hbalm4 ,,sketch ,,made ,,in #aijf - to face p4 #aef ,,plate ,,xx4 ,,schiaparelli',s ,,map ,,of ,,mars ,,of #ahhb1 ,,and ,,additions 7,,in ,,red7 ,,of #ahib - to face p4 #aff ,,plate ,,xxi4 ,,globe ,,of ,,mars ,,showing ,,path ,,of ,,in-,,falling ,,satellite - to face p4 #ahh ,,plate ,,xxii4 ,,canals ,,mapped ,,by ,,lowell ,,compared ,,with ,,canals ,,formed ,,by ,,in-,,falling ,,satellites - to face p4 #aib ,,plate ,,xxiii4 ,,haloes ,,in ,,mica2 ,,co4 ,,carlow4 ,,halo ,,in ,,biotite ,,contained ,,in ,,granite - to face p4 #bbd ,,plate ,,xxiv4 ,,radium ,,halo1 ,,much ,,enlarged4 ,,thorium ,,halo ,,and ,,radium ,,halo ,,in ,,mica - to face p4 #bbh ,,plate ,,xxv4 ,,halo ,,round ,,capillary ,,in ,,glass ,,tube4 ,,haloes ,,round ,,tubular ,,passages ,,in ,,mica - to face p4 #bcj ,,plate ,,xxvi4 ,,aletsch ,,glacier1 ,,switzerland - to face p4 #bhb ,,plate ,,xxvii4 ,,the ,,middle ,,aletsch ,,glacier ,,joining ,,the ,,great ,,aletsch ,,glacier4 ,,glaciers ,,of ,,the ,,lauterbrunnen ,,thal - to face p4 #bhe ,,plate ,,xxviii4 ,,perched ,,block ,,on ,,the ,,aletsch ,,glacier4 ,,granite ,,erratic ,,near ,,roundwood1 ,,co4 ,,wicklow2 ,,now ,,broken ,,up ,,and ,,removed - to face p4 #bhf ,and ,fifteen ,illustrations in the ,text4 x ,,preface ,tins volume contains twelve essays written at various times during recent years4 ,many of them are studies contributed to ,scientific ,reviews or delivered as popular lectures4 ,some are expositions of views the scientific basis of which may be regarded as established4 ,others--the greater number--may be described as attempting the solution of problems which cannot be approached by direct observation4 ,the essay on ,the ,birth-time of the ,world is based on a lecture delivered before the ,royal ,dublin ,society4 ,the subject has attracted much attention within recent years4 ,the age of the ,earth is1 indeed1 of primary importance in our conception of the longevity of planetary systems4 ,the essay deals with the evidence1 derived from the investigation of purely terrestrial phenomena1 as to the period which has elapsed since the ocean condensed upon the ,earth's surface4 ,dr4 ,decker's recent addition to the subject appeared too late for inclusion in it4 ,he finds that the movements 7termed isostatic7 which geologists recognise as taking place deep in the ,earth's crust1 indicate an age of the same order of magnitude xi as that which is inferred from the statistics of denudative history4#a ,the subject of ,denudation naturally arises from the first essay4 ,in thinking over the method of finding the age of the ocean by the accumulation of sodium therein1 ,i perceived so long ago as #ahii1 when my first paper was published1 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 time2 the resulting knowledge in no way involving any assumption as to the duration of the period comprising the denudative actions4 ,this idea has been elaborated in various publications since then1 both by myself and by others4 ,denudation1 while including a survey of the subject generally1 is mainly a popular account of this method and its results4 ,it closes with a reference to the fascinating problems presented by the inner nature of sedimentation3 a branch of science to which ,i endeavoured to contribute some years ago4 ,mountain ,genesis first brings in the subject of the geological intervention of radioactivity4 ,there can1 ,i believe1 be no doubt as to the influence of transforming elements upon the developments of the surface features of the ,earth2 and1 if ,i am right1 this source of thermal energy is mainly responsible for that local accumulation of wrinkling which we term mountain chains4 ,the #a ,bull4 ,geol4 ,soc4 ,america1 vol4 xxvi1 ,march #aiae4 xii paper on ,alpine ,structure is a reprint from ,radioactivity and ,geology1 which for the sake of completeness is here included4 ,it is directed to the elucidation of a detail of mountain genesis3 a detail which enters into recent theories of ,alpine development4 ,the weakness of the theory of the horst is manifest1 however1 in many of its other applications2 if not1 indeed1 in all4 ,the foregoing essays on the physical influences affecting the surface features of the ,earth are accompanied by one entitled ,the ,abundance of ,life4 ,this originated amidst the overwhelming presentation of life which confronts us in the ,swiss ,alps4 ,the subject is sufficiently inspiring4 ,can no fundamental reason be given for the urgency and aggressiveness of life8 ,vitality is an ever-extending phenomenon4 ,it is plain that the great principles which have been enunciated in explanation of the origin of species do not really touch the problem4 ,in the essay--which is an early one 7#ahij7--the explanation of the whole great matter is sought--and as ,i believe found--in the attitude of the organism towards energy external to it2 an attitude which results in its evasion of the retardative and dissipatory effects which prevail in lifeless dynamic systems of all kinds4 ,other ,minds than ,ours8 attempts a solution of the vexed question of the origin of the ,martian canals4 ,the essay is an abridgment of two popular lectures on the subject4 ,i had previously written an account of my views which carried the enquiry as far as it was in xiii my power to go4 ,this paper appeared in the ,transactions of the ,royal ,dublin ,society1 #ahig4 ,the theory put forward is a purely physical one1 and1 if justified1 the view that intelligent beings exist in ,mars derives no support from his visible surface features2 but is1 in fact1 confronted with fresh difficulties4 ,pleochroic ,haloes is a popular exposition of an inconspicuous but very beautiful phenomenon of the rocks4 ,minute darkened spheres--a microscopic detail--appear everywhere in certain of the rock minerals4 ,what are they8 ,the discoveries of recent radioactive research--chiefly due to ,rutherford--give the answer4 ,the measurements applied to the little objects render the explanation beyond question4 ,they turn out to be a quite extraordinary record of radioactive energy2 a record accumulated since remote geological times1 and assuring us1 indirectly1 of the stability of the chemical elements in general since the beginning of the world4 ,this assurance is1 without proof1 often assumed in our views on the geological history of the ,globe4 ,skating is a discourse1 with a recent addition supporting the original thesis4 ,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 resources4 ,the address on ,the ,latent ,image deals with a subject which had been approached by various writers before the time of my essay2 but1 so far as ,i know1 an explanation xiv based on the facts of photo-electricity had not been attempted4 ,students of this subject will notice that the views expressed are similar to those subsequently put forward by ,lenard and ,saeland in explanation of phosphorescence4 ,the whole matter is of more practical importance than appears at first sight1 for the photoelectric nature of the effects involved in the radiative treatment of many cruel diseases seems to be beyond doubt4 ,it was in connection with photo-electric science that ,i was led to take an interest in the application of radioactivity in medicine4 ,the lecture on ,the ,use of ,radium in ,medicine deals with this subject4 ,towards the conclusion of this essay reference will be found to a practical outcome of such studies which1 by improving on the methods1 and facilitating the application1 of radioactive treatment1 has1 in the hands of skilled medical men1 already resulted in the alleviation of suffering4 ,leaving out much which might well appear in a prefatory notice1 a word should yet be added respecting the illustrations of scenery4 ,they are a small selection from a considerable number of photographs taken during my summer wanderings in the ,alps in company with ,henry ,h4 ,dixon4 ,an exception is ,plate ,x1 which is by the late ,dr4 ,edward ,stapleton4 ,from what has been said above1 it will be gathered that these illustrations are fitly included among pages which owe so much to ,alpine inspiration4 ,they illustrate the xv subjects dealt with1 and1 it is to be hoped1 they will in some cases recall to the reader scenes which have in past times influenced his thoughts in the same manner2 scenes which in their endless perspective seem to reduce to their proper insignificance the lesser things of life4 ,my thanks are due to ,mr4 ,john ,murray for kindly consenting to the reissue of the essay on ,the ,birth-time of the ,world from the pages of ,science ,progress2 to ,messrs4 ,constable ,co4 for leave to reprint ,pleochroic ,haloes from ,bedrock1 and also to make some extracts from ,radioactivity and ,geology2 and to the ,council of the ,royal ,dublin ,society for permission to republish certain papers from the ,proceedings of the ,society4 ,iveagh ,geological ,laboratory1 ,trinity ,college1 ,dublin4 ,july1 #aiae4 xvi ,,the ,,birth-,,time ,,of ,,the ,,world #a ,,long ago ,lucretius wrote3 ,for lack of power to solve the question troubles the mind with doubts1 whether there was ever a birth-time of the world and whether likewise there is to be any end4 ,and if 7he says in answer7 there was no birth-time of earth and heaven and they have been from everlasting1 why before the ,theban war and the destruction of ,troy have not other poets as well sung other themes8 ,whither have so many deeds of men so often passed away1 why live they nowhere embodied in lasting records of fame8 ,the truth methinks is that the sum has but a recent date1 and the nature of the world is new and has but lately had its commencement4#b ,thus spake ,lucretius nearly #b1jjj years ago4 ,since then we have attained another standpoint and found very different limitations4 ,to ,lucretius the world commenced with man1 and the answer he would give to his questions was in accord with his philosophy3 he would date the birth-time of the world from the time when #a ,a lecture delivered before the ,royal ,dublin ,society1 ,february #fth1 #aiad4 ,science ,progress1 vol4 ix41 p4 #cg #b ,de ,rerum ,natura1 translated by ,h4 ,a4 ,j4 ,munro 7,cambridge1 #ahhf74 #a poets first sang upon the earth4 ,modern ,science has along with the theory that the ,earth dated its beginning with the advent of man1 swept utterly away this beautiful imagining4 ,we can1 indeed1 find no beginning of the world4 ,we trace back events and come to barriers which close our vista--barriers which1 for all we know1 may for ever close it4 ,they stand like the gates of ivory and of horn2 portals from which only dreams proceed2 and ,science cannot as yet say of this or that dream if it proceeds from the gate of horn or from that of ivory4 ,in short1 of the ,earth's origin we have no certain knowledge2 nor can we assign any date to it4 ,possibly its formation was an event so gradual that the beginning was spread over immense periods4 ,we can only trace the history back to certain events which may with considerable certainty be regarded as ushering in our geological era4 ,notwithstanding our limitations1 the date of the birth-time of our geological era is the most important date in ,science4 ,for in taking into our minds the spacious history of the universe1 the world's age must play the part of time-unit upon which all our conceptions depend4 ,if we date the geological history of the ,earth by thousands of years1 as did our forerunners1 we must shape our ideas of planetary time accordingly2 and the duration of our solar system1 and of the heavens1 becomes comparable with that of the dynasties of ancient nations4 ,if by millions of years1 the sun and stars are proportionately venerable4 ,if by hundreds or thousands of millions of #b years the human mind must consent to correspondingly vast epochs for the duration of material changes4 ,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 space4 ,lucretius knew nothing of our time-unit3 his unit was the life of a man4 ,so also he knew nothing of our space-unit1 and he marvels that so small a body as the sun can shed so much1 heat and light upon the ,earth4 ,a study of the rocks shows us that the world was not always what it now is and long has been4 ,we live in an epoch of denudation4 ,the rains and frosts disintegrate the hills2 and the rivers roll to the sea the finely divided particles into which they have been resolved2 as well as the salts which have been leached from them4 ,the sediments collect near the coasts of the continents2 the dissolved matter mingles with the general ocean4 ,the geologist has measured and mapped these deposits and traced them back into the past1 layer by layer4 ,he finds them ever the same2 sandstones1 slates1 limestones1 etc4 ,but one thing is not the same4 ,life grows ever less diversified in character as the sediments are traced downwards4 ,mammals and birds1 reptiles1 amphibians1 fishes1 die out successively in the past2 and barren sediments ultimately succeed1 leaving the first beginnings of life undecipherable4 ,beneath these barren sediments lie rocks collectively differing in character from those above3 mainly volcanic or poured out from fissures in #c the early crust of the ,earth4 ,sediments are scarce among these materials4#a ,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 began1 and before the seas came into being4 ,they formed the floor of a vaporised ocean upon which the waters condensed here and there from the hot and heavy atmosphere4 ,such were the probable conditions which preceded the birth-time of the ocean and of our era of life and its evolution4 ,it is from this epoch we date our geological age4 ,our next purpose is to consider how long ago1 measured in years1 that birth-time was4 ,that the geological age of the ,earth is very great appears from what we have already reviewed4 ,the sediments of the past are many miles in collective thickness3 yet the feeble silt of the rivers built them all from base to summit4 ,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 visible4 ,the mountains have again been worn down into the ocean by denudation and again younger mountains built out of their redeposited materials4 ,the contemplation of such vast events #a ,for a description of these early rocks1 see especially the monograph of ,van ,hise and ,leith on the pre-,cambrian ,geology of ,north ,america 7,bulletin #cfj1 ,u4,s4 ,geol4 ,survey74 #d prepares our minds to accept many scores of millions of years or hundreds of millions of years1 if such be yielded by our calculations4 ,,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 periods4 ,the method has undergone much revision from time to time4 ,let us briefly review it on the latest data4 ,the method consists in measuring the depths of all the successive sedimentary deposits where these are best developed4 ,we go all over the explored world1 recognising the successive deposits by their fossils and by their stratigraphical relations1 measuring their thickness and selecting as part of the data required those beds which we believe to most completely represent each formation4 ,the total of these measurements would tell us the age of the ,earth if their tale was indeed complete1 and if we knew the average rate at which they have been deposited4 ,we soon1 however1 find difficulties in arriving at the quantities we require4 ,thus it is not easy to measure the real thickness of a deposit4 ,it may be folded back upon itself1 and so we may measure it twice over4 ,we may exaggerate its thickness by measuring it not quite straight across the bedding or by unwittingly including volcanic materials4 ,on the other hand1 there #e may be deposits which are inaccessible to us2 or1 again1 an entire absence of deposits2 either because not laid down in the areas we examine1 or1 if laid down1 again washed into the sea4 ,these sources of error in part neutralise one another4 ,some make our resulting age too long1 others make it out too short4 ,but we do not know if a balance of error does not still remain4 ,here1 however1 is a table of deposits which summarises a great deal of our knowledge of the thickness of the stratigraphical accumulations4 ,it is due to ,sollas4#a ,feet4 ,recent and ,pleistocene - - #d1jjj ,pliocene - - #ac1jjj ,miocene - - #ad1jjj ,oligocene - - #b1jjj ,eocene - - #bj1jjj #fc1jjj ,upper ,cretaceous - - #bd1jjj ,lower ,cretaceous - - #bj1jjj ,jurassic - - #h1jjj ,trias - - #g1jjj #fi1jjj ,permian - - #b1jjj ,carboniferous - - #bi1jjj ,devonian - - #bb1jjj #fc1jjj ,silurian - - #ae1jjj ,ordovician - - #ag1jjj ,cambrian - - #f1jjj #eh1jjj ,algonkian--,keeweenawan - - #ej1jjj ,algonkian--,animikian - - #ad1jjj ,algonkian--,huronian - - #ah1jjj #hb1jjj ,archan - - 8 ,total - - #cce1jjj feet4 #a ,address to the ,geol4 ,soc4 of ,london1 #aeji4 #f ,in the next place we require to know the average rate at which these rocks were laid down4 ,this is really the weakest link in the chain4 ,the most diverse results have been arrived at1 which space does not permit us to consider4 ,the value required is most difficult to determine1 for it is different for the different classes of material1 and varies from river to river according to the conditions of discharge to the sea4 ,we may probably take it as between two and six inches in a century4 ,now the total depth of the sediments as we see is about #cce1jjj feet 7or #fd miles71 and if we take the rate of collecting as three inches in a hundred years we get the time for all to collect as #acd millions of years4 ,if the rate be four inches1 the time is soo millions of years1 which is the figure ,geikie favoured1 although his result was based on somewhat different data4 ,sollas most recently finds #hj millions of years4#a ,,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 sediments4 ,these measurements1 as we have seen1 are difficult to arrive at4 ,we may1 however1 proceed by measurements of the mass of the sediments1 and then the method becomes more definite4 ,the new method is pursued as follows3 #a ,geikie1 ,text ,book of ,geology 7,macmillan1 #aijc71 vol4 i41 p4 #gc1 et seq4 ,sollas1 loc4 cit4 ,joly1 ,radioactivity and ,geology 7,constable1 #aiji71 and ,phil4 ,mag41 ,sept4 #aiaa4 #g ,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 ocean4 ,the salts in the ocean are undoubtedly derived from the rocks2 increasing age by age as the latter are degraded from their original character under the action of the weather1 etc41 and converted to the sedimentary form4 ,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 form4 ,this1 however1 will not assist us to our object unless the ocean has retained the salts shed into it4 ,it has not generally done so4 ,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 rivers4 ,the one exception is the element sodium4 ,the great solubility of its salts has protected it from abstraction1 and it has gone on collecting during geological time1 practically in its entirety4 ,this gives us the clue to the denudative history of the ,earth4#a ,the process is now simple4 ,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 denudation4 ,we also calculate #a ,trans4 ,r4,d4,s41 ,may1 #ahii4 #h the amount of sodium contained in the ocean4 ,we divide the one into the other 7stated1 of course1 in the same units of mass71 and the quotient gives us the number of tons of sediment4 ,the most recent estimate of the sediments made in this manner affords #ef x #ajaf tonnes4#a ,now we are assured that all this sediment was transported by the rivers to the sea during geological time4 ,thus it follows that1 if we can estimate the average annual rate of the river supply of sediments to the ocean over the past1 we can calculate the required age4 ,the land surface is at present largely covered with the sedimentary rocks themselves4 ,sediment derived from these rocks must be regarded as1 for the most part1 purely cyclical2 that is1 circulating from the sea to the land and back again4 ,it does not go to increase the great body of detrital deposits4 ,we cannot1 therefore1 take the present river supply of sediment as representing that obtaining over the long past4 ,if the land was all covered still with primary rocks we might do so4 ,it has been estimated that about #be per cent4 of the existing continental area is covered with archan and igneous rocks1 the remainder being sediments4#b ,on this estimate we may find valuable #a ,clarke1 ,a ,preliminary ,study of ,chemical ,denudation 7,washington1 #aiaj74 ,my own estimate in #ahii 7loc4 cit47 made as a test of yet another method of finding the age1 showed that the sediments may be taken as sufficient to form a layer #a4a mile deep if spread uniformly over the continents2 and would amount to #fd x #ajah tons4 #b ,van ,tillo1 ,comptes ,rendues 7,paris71 vol4 cxiv41 #ahib4 #i major and minor limits to the geological age4 ,if we take #be per cent4 only of the present river supply of sediment1 we evidently fix a major limit to the age1 for it is certain that over the past there must have been on the average a faster supply4 ,if we take the entire river supply1 on similar reasoning we have what is undoubtedly a minor limit to the age4 ,the river supply of detrital sediment has not been very extensively investigated1 although the quantities involved may be found with comparative ease and accuracy4 ,the following table embodies the results obtained for some of the leading rivers4#a ,mean annual ,total annual ,ratio of discharge in sediment in sediment cubic feet thousands to water per second4 of tons4 by weight4 ,potomac - #bj1afj #e1eeg #a 3 #c4ege ,mississippi - #faj1jjj #djf1bej #a 3 #a1ejj ,rio ,grande - #a1gjj #c1hcj #a 3 #bia ,uruguay - #aej1jjj #ad1ghb #a 3 #aj1jjj ,rhone - #fe1hej #cf1jjj #a 3 #a1gge ,po - #fb1bjj #fg1jjj #a 3 #ijj ,danube - #cae1bjj #ajh1jjj #a 3 #b1hhj ,nile - #aac1jjj #ed1jjj #a 3 #b1jej ,irrawaddy - #dge1jjj #bia1dcj #a 3 #a1faj ,mean - #bja1dfh #aji1fej #a 3 #b1gca ,we see that the ratio of the weight of water to the #a ,russell1 ,river ,development 7,john ,murray1 #ahhh74 #aj weight of transported sediment in six out of the nine rivers does not vary widely4 ,the mean is #b1gcj to #a4 ,but this is not the required average4 ,the water-discharge of each river has to be taken into account4 ,if we ascribe to the ratio given for each river the weight proper to the amount of water it discharges1 the proportion of weight of water to weight of sediment1 for the whole quantity of water involved1 comes out as #b1ebj to #a4 ,now if this proportion holds for all the rivers of the world--which collectively discharge about #bg x #ajab tonnes of water per annum--the river-born detritus is #a4jg x #ajaj tonnes4 ,to this an addition of #aa per cent4 has to be made for silt pushed along the river-bed4#a ,on these figures the minor limit to the age comes out as #dg millions of years1 and the major limit as #ahh millions4 ,we are here going on rather deficient estimates1 the rivers involved representing only some #f per cent4 of the total river supply of water to the ocean4 ,but the result is probably not very far out4 ,we may arrive at a probable age lying between the major and minor limits4 ,if1 first1 we take the arithmetic mean of these limits1 we get #aag millions of years4 ,now this is almost certainly excessive1 for we here assume that the rate of covering of the primary rocks by sediments was uniform4 ,it would not be so1 however1 for the rate of supply of original sediment must have been continually diminishing #a ,according to observations made on the ,mississippi 7,russell1 loc4 cit474 #aa during geological time1 and hence we may assume that the rate of advance of the sediments on the primary rocks has also been diminishing4 ,now we may probably take1 as a fair assumption1 that the sediment-covered area was at any instant increasing at a rate proportionate to the rate of supply of sediment2 that is1 to the area of primary rocks then exposed4 ,on this assumption the age is found to be #hg millions of years4 ,,the ,,age ,,by ,,the ,,sodium ,,of ,,the ,,ocean ,i have next to lay before you a quite different method4 ,i have already touched upon the chemistry of the ocean1 and on the remarkable fact that the sodium contained in it has been preserved1 practically1 in its entirety from the beginning of geological time4 ,that the sea is one of the most beautiful and magnificent sights in ,nature1 all admit4 ,but1 ,i think1 to those who know its story its beauty and magnificence are ten-fold increased4 ,its saltness it due to no magic mill4 ,it is the dissolved rocks of the ,earth which give it at once its brine1 its strength1 and its buoyancy4 ,the rivers which we say flow with fresh water to the sea nevertheless contain those traces of salt which1 collected over the long ages1 occasion the saltness of the ocean4 ,each gallon of river water contributes to the final result2 and this has been going on since the beginning of our era4 ,the mighty total of the rivers is #f1ejj cubic miles of water in the year6 #ab ,there is little doubt that the primeval ocean was in the condition of a fresh-water lake4 ,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 salinity4 ,the fact is1 the quantity of salts in the ocean is enormous4 ,we are only now concerned with the sodium2 but if we could extract all the rock-salt 7the chloride of sodium7 from the ocean we should have enough to cover the entire dry land of the ,earth to a depth of #djj feet4 ,it is this gigantic quantity which is going to enter into our estimate of the ,earth's age4 ,the calculated mass of sodium contained in this rock-salt is #ad1acj million million tonnes4 ,if now we can determine the rate at which the rivers supply sodium to the ocean1 we can determine the age4#a ,as the result of many thousands of river analyses1 the total amount of sodium annually discharged to the ocean #a ,trans4 ,r4,d4,s41 #ahii4 ,a paper by ,edmund ,halley1 the astronomer1 in the ,philosophical ,transactions of the ,royal ,society for #agae1 contains a suggestion for finding the age of the world by the following procedure4 ,he proposes to make observations on the saltness of the seas and ocean at intervals of one or more centuries1 and from the increment of saltness arrive at their age4 ,the measurements1 as a matter of fact1 are impracticable4 ,the salinity would only gain 7if all remained in solution7 one millionth part in ,too years2 and1 of course1 the continuous rejection of salts by the ocean would invalidate the method4 ,the last objection also invalidates the calculation by ,t4 ,mellard ,reade 7,proc4 ,liverpool ,geol4 ,soc41 #ahgf7 of a minor limit to the age by the calcium sulphate in the ocean4 ,both papers were quite unknown to me when working out my method4 ,halley's paper was1 ,i think1 only brought to light in #aijh4 #ac by all the rivers of the world is found to be probably not far from #age million tonnes4#a ,dividing this into the mass of oceanic sodium we get the age as #hj4g millions of years4 ,certain corrections have to be applied to this figure which result in raising it to a little over #ij millions of years4 ,sollas1 as the result of a careful review of the data1 gets the age as between #hj and #aej millions of years4 ,my own result#b was between #hj and #ij millions of years2 but ,i subsequently found that upon certain extreme assumptions a maximum age might be arrived at of #aje millions of years4#c ,clarke regards the #hj4g millions of years as certainly a maximum in the light of certain calculations by ,becker4#d ,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 denudation4 ,on the strength of the results of another and #a ,f4 ,w4 ,clarke1 ,a ,preliminary ,study of ,chemical ,denudation 7,smithsonian ,miscellaneous ,collections1 #aiaj74 #b ,loc4 cit4 #c ,the ,circulation of ,salt and ,geological ,time 7,geol4 ,mag41 #aija1 p4 #cej74 #d ,becker 7loc4 cit471 assuming that the exposed igneous and archan rocks alone are responsible for the supply of sodium to the ocean1 arrives at #gd millions of years as the geological age4 ,this matter was discussed by me formerly 7,trans4 ,r4,d4,s41 #ahii1 pp4 #ed et seq474 ,the assumption made is1 ,i believe1 inadmissible4 ,it is not supported by river analyses1 or by the chemical character of residual soils from sedimentary rocks4 ,there may be some convergence in the rate of solvent denudation1 but--as ,i think on the evidence--in our time unimportant4 #ad entirely different method of approaching the question of the ,earth's age 7which shall be presently referred to71 it has been contended that it is too low4 ,it is even asserted that it is from nine to fourteen times too low4 ,we have then to consider whether such an enormous error can enter into the method4 ,the measurements involved cannot be seriously impugned4 ,corrections for possible errors applied to the quantities entering into this method have been considered by various writers4 ,my own original corrections have been generally confirmed4 ,i think the only point left open for discussion is the principle of uniformitarianism involved in this method and in the methods previously discussed4 ,in order to appreciate the force of the evidence for uniformity in the geological history of the ,earth1 it is1 of course1 necessary to possess some acquaintance with geological science4 ,some of the most eminent geologists1 among whom ,lyell and ,geikie#a may be mentioned1 have upheld the doctrine of uniformity4 ,it must here suffice to dwell upon a few points having special reference to the matter under discussion4 ,the mere extent of the land surface does not1 within limits1 affect the question of the rate of denudation4 ,this arises from the fact that the rain supply is quite insufficient to denude the whole existing land surface4 ,about #cj per cent4 of it does not1 in fact1 drain to the #a ,see especially ,geikie's ,address to ,sect4 ,c41 ,brit4 ,assoc4 ,rep41 #acii4 #ae ocean4 ,if the continents become invaded by a great transgression of the ocean1 this rainless area diminishes3 and the denuded area advances inwards without diminution4 ,if the ocean recedes from the present strand lines1 the rainless area advances outwards1 but1 the rain supply being sensibly constant1 no change in the river supply of salts is to be expected4 ,age-long submergence of the entire land1 or of any very large proportion of what now exists1 is negatived by the continuous sequence of vast areas of sediment in every geologic age from the earliest times4 ,now sediment-receiving areas always are but a small fraction of those exposed areas whence the sediments are supplied4#a ,hence in the continuous records of the sediments we have assurance of the continuous exposure of the continents above the ocean surface4 ,the doctrine of the permanency of the continents has in its main features been accepted by the most eminent authorities4 ,as to the actual amount of land which was exposed during past times to denudative effects1 no data exist to show it was very different from what is now exposed4 ,it has been estimated that the average area of the ,north ,american continent over geologic time was about eight-tenths of its existing area4#b ,restorations of other continents1 so far as they have been attempted1 would not #a ,on the strength of the ,mississippi measurements about #a to #ah 7,magee1 ,am4 ,jour4 of ,sc41 #ahib1 p4 #ahh74 #b ,schuchert1 ,bull4 ,geol4 ,soc4 ,am41 vol4 xx41 #aiaj4 #af suggest any more serious divergency one way or the other4 ,that climate in the oceans and upon the land was throughout much as it is now1 the continuous chain of teeming life and the sensitive temperature limits of protoplasmic existence are sufficient evidence4#a ,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 denudation1 as the following table shows4 ,tonnes removed in ,mean elevation4 solution per square ,metres4 mile per annum4 ,north ,america - #gi #gjj ,south ,america - #ej #fej ,europe - #ajj #cjj ,asia - #hd #iej ,africa - #dd #fej ,in this table the estimated number of tonnes of matter in solution1 which for every square mile of area the rivers convey to the ocean in one year1 is given in the first column4 ,these results are compiled by ,clarke from a very large number of analyses of river waters4 ,the second column of the table gives the mean heights in metres above sea level of the several continents1 as cited by ,arrhenius4#b ,of all the denudation results given in the table1 those relating to ,north ,america and to ,europe are far the #a ,see also ,poulton1 ,address to ,sect4 ,d41 ,brit4 ,assoc4 ,rep41 #ahif4 #b ,lehybuch dev ,kosmischen ,physik1 vol4 i41 p4 #cdg4 #ag most reliable4 ,indeed these may be described as highly reliable1 being founded on some thousands of analyses1 many of which have been systematically pursued through every season of the year4 ,these show that ,europe with a mean altitude of less than half that of ,north ,america sheds to the ocean #be per cent4 more salts4 ,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 respectively3 conditions in many cases antagonistic4#a ,hence if it is true1 as has been stated1 that we now live in a period of exceptionally high continental elevation1 we must infer that the average supply of salts to the ocean by the rivers of the world is less than over the long past1 and that1 therefore1 our estimate of the age of the ,earth as already given is excessive4 ,there is1 however1 one condition which will operate to unduly diminish our estimate of geologic time1 and it is a condition which may possibly obtain at the present time4 ,if the land is1 on the whole1 now sinking relatively to the ocean level1 the denudation area tends1 as we have seen1 to move inwards4 ,it will thus encroach upon regions which have not for long periods drained to the ocean4 ,on such areas there is an accumulation of soluble salts which the deficient rivers have not been able to carry to the ocean4 ,thus the salt content of certain of #a ,see the essay on ,denudation4 #ah the rivers draining to the ocean will be influenced not only by present denudative effects1 but also by the stored results of past effects4 ,certain rivers appear to reveal this unduly increased salt supply those which flow through comparatively arid areas4 ,however1 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 account4 ,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 latter4 ,,the ,,age ,,by ,,radioactive ,,transformations ,rutherford suggested in #aije that as helium was continually being evolved at a uniform rate by radioactive substances 7in the form of the alpha rays7 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 it1 ,the parent radioactive substances are--according to present knowledge--uranium and thorium4 ,an estimate of the amounts of these elements present enables the rate of production of the helium to be calculated4 ,rutherford shortly afterwards found by this method an age of #bdj millions of years for a radioactive mineral of presumably remote age4 ,strutt1 who carried #ai his measurements to a wonderful degree of refinement1 found the following ages for mineral substances originating in different geological ages3 ,oligocene - #h4d millions of years4 ,eocene - #ca millions of years4 ,lower ,carboniferous - #aej millions of years4 ,archan - #gej millions of years4 ,periods of time much less than1 and very inconsistent with1 these were also found4 ,the lower results are1 however1 easily explained if we assume that the helium--which is a gas under prevailing conditions--escapes in many cases slowly from the mineral4 ,another product of radioactive origin is lead4 ,the suggestion that this substance might be made available to determine the age of the ,earth also originated with ,rutherford4 ,we are at least assured that this element cannot escape by gaseous diffusion from the minerals4 ,boltwood's results on the amount of lead contained in minerals of various ages1 taken in conjunction with the amount of uranium or parent substance present1 afforded ages rising to #a1fdj millions of years for archan and #a1bjj millions for ,algonkian time4 ,becker1 applying the same method1 obtained results rising to quite incredible periods3 from #a1fga to #aa1dgj millions of years4 ,becker maintained that original lead rendered the determinations indefinite4 ,the more recent results of ,mr4 ,a4 ,holmes support the conclusion that original lead may be present and may completely falsify results derived #bj from minerals of low radioactivity in which the derived lead would be small in amount4 ,by rejecting such results as appeared to be of this character1 he arrives at #cgj millions of years as the age of the ,devonian4 ,i must now describe a very recent method of estimating the age of the ,earth4 ,there are1 in certain rock-forming minerals1 colour-changes set up by radioactive causes4 ,the minute and curious marks so produced are known as haloes2 for they surround1 in ringlike forms1 minute particles of included substances which contain radioactive elements4 ,it is now well known how these haloes are formed4 ,the particle in the centre of the halo contains uranium or thorium1 and1 necessarily1 along with the parent substance1 the various elements derived from it4 ,in the process of transformation giving rise to these several derived substances1 atoms of helium--the alpha rays--projected with great velocity into the surrounding mineral1 occasion the colour changes referred to4 ,these changes are limited to the distance to which the alpha rays penetrate2 hence the halo is a spherical volume surrounding the central substance4#a ,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 in1 say1 one year1 and1 on the other1 if we determined by experiment just how many alpha rays were required to produce the same #a ,phil4 ,mag41 ,march1 #aijg and ,february1 #aiaj2 also ,bedrock1 ,january1 #aiac4 ,see ,pleochroic ,haloes in this volume4 #ba amount of colour alteration as we perceive to extend around the nucleus4 ,the latter estimate is fairly easily and surely made4 ,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 nucleus4 ,this cannot be directly determined4 ,we can only1 from known results obtained with larger specimens of just such a mineral substance as composes the nucleus1 guess at the amount of uranium1 or it may be thorium1 which may be present4 ,this method has been applied to the uranium haloes of the mica of ,county ,carlow4#a ,results for the age of the halo of from #bj to #djj millions of years have been obtained4 ,this mica was probably formed in the granite of ,leinster in late ,silurian or in ,devonian times4 ,the higher results are probably the least in error1 upon the data involved2 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 reliable4 ,this method is1 of course1 a radioactive method1 and similar to the method by helium storage1 save that it is free of the risk of error by escape of the helium1 the effects of which are1 as it were1 registered at the moment of its production1 so that its subsequent escape is of no moment4 #a ,joly and ,rutherford1 ,phil4 ,mag41 ,april1 #aiac4 #bb ,,review ,,of ,,the ,,results ,we shall now briefly review the results on the geological age of the ,earth4 ,by methods based on the approximate uniformity of denudative effects in the past1 a period of the order of #ajj millions of years has been obtained as the duration of our geological age2 and consistently whether we accept for measurement the sediments or the dissolved sodium4 ,we can give reasons why these measurements might afford too great an age1 but we can find absolutely no good reason why they should give one much too low4 ,by measuring radioactive products ages have been found which1 while they vary widely among themselves1 yet claim to possess accuracy in their superior limits1 and exceed those derived from denudation from nine to fourteen times4 ,in this difficulty let us consider the claims of the radioactive method in any of its forms4 ,in order to be trustworthy it must be true2 7#a7 that the rate of transformation now shown by the parent substance has obtained throughout the entire past1 and 7#b7 that there were no other radioactive substances1 either now or formerly existing1 except uranium1 which gave rise to lead4 ,as regards methods based on the production of helium1 what we have to say will largely apply to it also4 ,if some unknown source of these elements exists we1 of course1 on our assumption overestimate the age4 #bc ,as regards the first point3 ,in ascribing a constant rate of change to the parent substance--which ,becker 7loc4 cit47 describes as a simple though tremendous extrapolation--we reason upon analogy with the constant rate of decay observed in the derived radioactive bodies4 ,if uranium and thorium are really primary elements1 however1 the analogy relied on may be misleading2 at least1 it is obviously incomplete4 ,it is incomplete in a particular which may be very important3 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 them4 ,a convergence in their rate of transformation is not impossible1 or even improbable1 so far as we known4 ,as regards the second point3 ,it is assumed that uranium alone of the elements in radioactive minerals is ultimately transformed to lead by radioactive changes4 ,we must consider this assumption4 ,recent advances in the chemistry of the radioactive elements has brought out evidence that all three lines of radioactive descent known to us--i4e4 those beginning with uranium1 with thorium1 and with actinium--alike converge to lead4#a ,there are difficulties in the way of believing that all the lead-like atoms so produced 7isotopes of lead1 as ,soddy proposes to call them7 actually remain as stable lead in the minerals4 ,for one #a ,see ,soddy's ,chemistry of the ,radioactive ,elements 7,longmans1 ,green ,co474 #bd thing there is sometimes1 along with very large amounts of thorium1 an almost entire absence of lead in thorianites and thorites4 ,and in some urano--thorites the lead may be noticed to follow the uranium in approximate proportionality1 notwithstanding the presence of large amounts of thorium4#a ,this is in favour of the assumption that all the lead present is derived from the uranium4 ,the actinium is present in negligibly small amounts4 ,on the other hand1 there is evidence arising from the atomic weight of lead which seems to involve some other parent than uranium4 ,soddy1 in the work referred to1 points this out4 ,the atomic weight of radium is well known1 and uranium in its descent has to change to this element4 ,the loss of mass between radium and uranium-derived lead can be accurately estimated by the number of alpha rays given off4 ,from this we get the atomic weight of uranium-derived lead as closely #bjf4 ,now the best determinations of the atomic weight of normal lead assign to this element an atomic weight of closely #a ,it seems very difficult at present to suggest an end product for thorium1 unless we assume that1 by loss of electrons1 thorium ,e1 or thorium-lead1 reverts to a substance chemically identical with thorium itself4 ,such a change--whether considered from the point of view of the periodic law or of the radioactive theory would involve many interesting consequences4 ,it is1 of course1 quite possible that the nature of the conditions attending the deposition of the uranium ores1 many of which are comparatively recent1 are responsible for the difficulties observed4 ,the thorium and uranium ores are1 again1 specially prone to alteration4 #be #bjg4 ,by a somewhat similar calculation it is deduced that thorium-derived lead would possess the atomic weight of #bjh4 ,thus normal lead might be an admixture of uranium- and thorium-derived lead4 ,however1 as we have seen1 the view that thorium gives rise to stable lead is beset with some difficulties4 ,if we are going upon reliable facts and figures1 we must1 then1 assume3 7a7 ,that some other element than uranium1 and genetically connected with it 7probably as parent substance71 gives rise1 or formerly gave rise1 to lead of heavier atomic weight than normal lead4 ,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 exists4 ,the evidence is found in the proportionality frequently observed between the amounts of thorium and uranium in the primary rocks4#a ,or3 7b7 ,we may meet the difficulties in a simpler way1 which may be stated as follows3 ,if we assume that all stable lead is derived from uranium1 and at the same time recognise that lead is not perfectly homogeneous in atomic weight1 we must1 of necessity1 ascribe to uranium a similar want of homogeneity2 heavy atoms of uranium giving rise to heavy #a ,compare results for the thorium content of such rocks 7appearing in a paper by the author ,cong4 ,int4 de ,radiologie et d',electricit1 vol4 i41 #aiaj1 p4 #cgc71 and those for the radium content1 as collected in ,phil4 ,mag41 ,october1 #aiab1 p4 #fig4 ,also ,a4 ,l4 ,fletcher1 ,phil4 ,mag41 ,july1 #aiaj2 ,january1 #aiaa1 and ,june1 #aiaa4 ,j4 ,h4 ,j4 ,poole1 ,phil4 ,mag41 ,april1 #aiae #bf atoms of lead and light atoms of uranium generating light atoms of lead4 ,this assumption seems to be involved in the figures upon1 which we are going4 ,still relying on these figures1 we find1 however1 that existing uranium cannot give rise to lead of normal atomic weight4 ,we can only conclude that the heavier atoms of uranium have decayed more rapidly than the lighter ones4 ,in this connection it is of interest to note the complexity of uranium as recently established by ,geiger1 although in this case it is assumed that the shorter-lived isotope bears the relation of offspring to the longer-lived and largely preponderating constituent4 ,however1 there does not seem to be any direct proof of this as yet4 ,from these considerations it would seem that unless the atomic weight of lead in uraninites1 etc41 is #bjf1 the former complexity and more accelerated decay of uranium are indicated in the data respecting the atomic weights of radium and lead#a4 ,as an alternative view1 we may assume1 as in our first hypothesis1 that some elementally different but genetically connected substance1 decaying along branching lines of descent at a rate sufficient to practically remove the whole of it during geological time1 formerly existed4 ,whichever hypothesis we adopt #a ,later investigation has shown that the atomic weight of lead in uranium-bearing ores is about #bjf4f 7see ,richards and ,lembert1 ,journ4 of ,am4 ,claem4 ,soc41 ,july1 #aiad74 ,this result gives support to the view expressed above4 #bg we are confronted by probabilities which invalidate time-measurements based on the lead and helium ratio in minerals4 ,we have1 in short1 grave reason to question the measure of uniformitarianism postulated in finding the age by any of the known radioactive methods4 ,that we have much to learn respecting our assumptions1 whether we pursue the geological or the radioactive methods of approaching the age of our era1 is1 indeed1 probable4 ,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 elements4 ,with this necessary admission we leave our study of the ,birth-,time of the ,world4 ,it has led us a long way from ,lucretius4 ,we do not ask if other ,iliads have perished2 or if poets before ,homer have vainly sung1 becoming a prey to all-consuming time4 ,we move in a greater history1 the landmarks of which are not the birth and death of kings and poets1 but of species1 genera1 orders4 ,and we set out these organic events not according to the passing generations of man1 but over scores or hundreds of millions of years4 ,how much ,lucretius has lost1 and how much we have gained1 is bound up with the question of the intrinsic value of knowledge and great ideas4 ,let us appraise knowledge as we would the ,homeric poems1 as some- #bh thing which ennobles life and makes it happier4 ,well1 then1 we are1 as ,i think1 in possession today of some of those lost ,iliads and ,odysseys for which ,lucretius looked in vain4#a #a ,the duration in the past of ,solar heat is necessarily bound up with the geological age4 ,there is no known means 7outside speculative science7 of accounting for more than about #cj million years of the existing solar temperature in the past4 ,in this direction the age seems certainly limited to #ajj million years4 ,see a review of the question by ,dr4 ,lindemann in ,nature1 ,april #eth1 #aiae4 #bi ,,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 deal4 ,while its great results are apparent even to the most casual observer1 the factors which have led to these results are in many cases so indeterminate1 and in some cases apparently so variable in influence1 that thoughtful writers have even claimed precisely opposite effects as originating from1 the same cause4 ,indeed1 it is almost impossible to deal with the subject without entering upon controversial matters4 ,in the following pages ,i shall endeavour to keep to broad issues which are1 at the present day1 either conceded by the greater number of authorities on the subject1 or are1 from their strictly quantitative character1 not open to controversy4 ,it is evident1 in the first place1 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 land1 and back again to the ocean4 ,an action entirely conditioned by solar heat1 and without which it would completely cease and further change upon the land come to an end4 ,to what actions1 then1 is so great a potency of the #cj circulating water to be traced8 ,broadly speaking1 we may classify them as mechanical and chemical4 ,the first involves the separation of rock masses into smaller fragments of all sizes1 down to the finest dust4 ,the second involves the actual solution in the water of the rock constituents1 which may be regarded as the final act of disintegration4 ,the rivers bear the burden both of the comminuted and the dissolved materials to the sea4 ,the mud and sand carried by their currents1 or gradually pushed along their beds1 represent the former2 the invisible dissolved matter1 only to be demonstrated to the eye by evaporation of the water or by chemical precipitation1 represents the latter4 ,the results of these actions1 integrated over geological time1 are enormous4 ,the entire bulk of the sedimentary rocks1 such as sandstones1 slates1 shales1 conglomerates1 limestones1 etc41 and the salt content of the ocean1 are due to the combined activity of mechanical and solvent denudation4 ,we shall1 later on1 make an estimate of the magnitude of the quantities actually involved4 ,in the ,swiss valleys we see torrents of muddy water hurrying along1 and if we follow them up1 we trace them to glaciers high among the mountains4 ,from beneath the foot of the glacier1 we find1 the torrent has birth4 ,the first debris given to the river is derived from the wearing of the rocky bed along which the glacier moves4 ,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 #ca ,the work of mechanical disintegration is1 however1 not restricted to the glacier's bed4 ,it proceeds everywhere over the surface of the rocks4 ,it is aided by the most diverse actions4 ,for instance1 the freezing and expansion of water in the chinks and cracks in those alpine heights where between sunrise and sunset the heat of summer reigns1 and between sunset and sunrise the cold of winter4 ,again1 under these conditions the mere change of surface temperature from night to day severely stresses the surface layers of the rocks1 and1 on the same principles as we explain the fracture of an unequally heated glass vessel1 the rocks cleave off in slabs which slip down the steeps of the mountain and collect as screes in the valley4 ,at lower levels the expansive force of vegetable growth is not unimportant1 as all will admit who have seen the strong roots of the pines penetrating the crannies of the rocks4 ,nor does the river which flows in the bed of the valley act as a carrier only4 ,listening carefully we may detect beneath the roar of the alpine torrent the crunching and knocking of descending boulders4 ,and in the potholes scooped by its whirling waters we recognise the abrasive action of the suspended sand upon the river bed4 ,a view from an ,alpine summit reveals a scene of remarkable desolation 7,pl4 ,v1 p4 #dj74 ,screes lie piled against the steep slopes4 ,cliffs stand shattered and ready to fall in ruins4 ,and here the forces at work readily reveal themselves4 ,an occasional wreath of white smoke among #cb the far-off peaks1 followed by a rumbling reverberation1 marks the fall of an avalanche4 ,water everywhere trickles through the shaly dbris scattered around4 ,in the full sunshine the rocks are almost too hot to bear touching4 ,a few hours later the cold is deadly1 and all becomes a frozen silence4 ,in such scenes of desolation and destruction1 detrital sediments are actively being generated4 ,as we descend into the valley we hear the deep voice of the torrents which are continually hurrying the disintegrated rocks to the ocean4 ,a remarkable demonstration of the activity of mechanical denudation is shown by the phenomenon of earth pillars4 ,the photograph 7,pl4 ,,iv47 of the earth pillars of the ,val d',hrens 7,switzerland7 shows the peculiar appearance these objects present4 ,they arise under conditions where large stones or boulders are scattered in a deep deposit of clay1 and where much of the denudation is due to water scour4 ,the large boulders not only act as shelter against rain1 but they bind and consolidate by their mere weight the clay upon which they rest4 ,hence the materials underlying the boulders become more resistant1 and as the surrounding clays are gradually washed away and carried to the streams1 these compacted parts persist1 and1 finally1 stand like walls or pillars above the general level4 ,after a time the great boulders fall off and the underlying clay becomes worn by the rainwash to fantastic spikes and ridges4 ,in the ,val d',hrens the earth pillars are formed #cc of the deep moraine stuff which thickly overlies the slopes of the valley4 ,the wall of pillars runs across the axis of the valley1 down the slope of the hill1 and crosses the road1 so that it has to be tunnelled to permit the passage of traffic4 ,it is not improbable that some additional influence--possibly the presence of lime--has hardened the material forming the pillars1 and tended to their preservation4 ,denudation has1 however1 other methods of work than purely mechanical2 methods more noiseless and gentle1 but not less effective1 as the victories of peace ate no less than those of war4 ,over the immense tracts of the continents chemical work proceeds relentlessly4 ,the rock in general1 more especially the primary igneous rock1 is not stable in presence of the atmosphere and of water4 ,some of the minerals1 such as certain silicates and carbonates1 dissolve relatively fast1 others with extreme slowness4 ,in the process of solution chemical actions are involved2 oxidation in presence of the free oxygen of the atmosphere2 attack by the feeble acid arising from the solution of carbon dioxide in water2 or1 again1 by the activity of certain acids--humous acids--which originate in the decomposition of vegetable remains4 ,these chemical agents may in some instances1 e4g4 in the case of carbonates such as limestone or dolomite--bring practically the whole rock into solution4 ,in other instances--e4g4 granites1 basalts1 etc4--they may remove some of the #cd constituent minerals completely or partially1 such as felspar1 olivine1 augite1 and leave more resistant substances to be ultimately washed down as fine sand or mud into the river4 ,it is often difficult or impossible to appraise the relative efficiency of mechanical and chemical denudation in removing the materials from a certain area4 ,there can be1 indeed1 little doubt that in mountainous regions the mechanical effects are largely predominant4 ,the silts of glacial rivers are little different from freshly-powdered rock4 ,the water which carries them but little different from the pure rain or snow which falls from the sky4 ,there has not been time for the chemical or solvent actions to take place4 ,now while gravitational forces favour sudden shock and violent motions in the hills1 the effect of these on solvent and chemical denudation is but small4 ,nor is good drainage favourable to chemical actions1 for water is the primary factor in every case4 ,water takes up and removes soluble combinations of molecules1 and penetrates beneath residual insoluble substances4 ,it carries the oxygen and acids downwards through the soils1 and finally conveys the results of its own work to the rivers and streams4 ,the lower mean temperature of the mountains as well as the perfect drainage diminishes chemical activities4 ,hence we conclude that the heights are not generally favourable to the purely solvent and chemical actions4 ,it is on the lower-lying land that soils tend to accumulate1 #ce and in these the chief solvent and the chief chemical denudation of the ,earth are effected4 ,the solvent and chemical effects which go on in the finely-divided materials of the soils may be observed in the laboratory4 ,they proceed faster than would be anticipated4 ,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 rock4 ,finally the water is analysed1 and in this manner the amount of dissolved matter it has taken up is estimated4 ,the rock powder is examined under the microscope in order to determine the size of the grains1 and so to calculate the total surface exposed to the action of the water4 ,we must be careful in such experiments to permit free oxidation by the atmosphere4 ,results obtained in this way of course take no account of the chemical effects of organic acids such as exist in the soils4 ,the quantities obtained in the laboratory will1 therefore1 be deficient as compared with the natural results4 ,in this manner it has been found that fresh basalt exposed to continually moving water will lose about #j4bj gramme per square metre of surface per year4 ,the mineral orthoclase1 which enters largely into the constitution of many granites1 was found to lose under the same conditions #j4jbe gramme4 ,a glassy lava 7obsidian7 rich in silica and in the chemical constituents of an average granite1 was more resistant still2 losing but #j4jac gramme per square metre per year4 ,hornblende1 a mineral #cf abundant in many rocks1 lost #j4jge gramme4 ,the mean of the results showed that #j4jh gramme was washed in a year from each square metre4 ,such results give us some indication of the rate at which the work of solution goes on in the finely divided soils4#a ,it might be urged that1 as the mechanical break up of rocks1 and the production in this way of large surfaces1 must be at the basis of solvent and chemical denudation1 these latter activities should be predominant in the mountains4 ,the answer to this is that the soils rarely owe their existence to mechanical actions4 ,the alluvium of the valleys constitutes only narrow margins to the rivers2 the finer dbris from the mountains is rapidly brought into the ocean4 ,the soils which cover the greater part of continental areas have had a very different origin4 ,in any quarry where a section of the soil and of the underlying rock is visible1 we may study the mode of formation of soils4 ,our observations are1 we will suppose1 pursued in a granite quarry4 ,we first note that the material of the soil nearest the surface is intermixed with the roots of grasses1 trees1 or shrubs4 ,examining a handful of this soil1 we see glistening flakes of mica which plainly are derived from the original granite4 ,washing off the finer particles1 we find the largest remaining grains are composed of the all but indestructible quartz4 #a ,proc4 ,roy4 ,irish ,acad41 ,,viii41 ,ser4 ,a1 p4 #ba4 #cg ,this also is from the granite4 ,some few of the grains are of chalky-looking felspar2 again a granitic mineral4 ,what is the finer silt we have washed off8 ,it1 too1 is composed of mineral particles to a great extent2 rock dust stained with iron oxide and intermixed with organic remains1 both animal and vegetable4 ,but if we make a chemical analysis of the finer silt we find that the composition is by no means that of the granite beneath4 ,the chemist is able to say1 from a study of his results1 that there has been1 in the first place1 a large loss of material attending the conversion of the granite to the soil4 ,he finds a concentration of certain of the more resistant substances of the granite arising from the loss of the less resistant4 ,thus the percentage amount of alumina is increased4 ,the percentage of iron is also increased4 ,but silica and most other substances show a diminished percentage4 ,notably lime has nearly disappeared4 ,soda is much reduced2 so is magnesia4 ,potash is not so completely abstracted4 ,finally1 owing to hydration1 there is much more combined water in the soil than in the rock4 ,this is a typical result for rocks of this kind4 ,deeper in the soil we often observe a change of texture4 ,it has become finer1 and at the same time the clay is paler in colour4 ,this subsoil represents the finer particles carried by rain from above4 ,the change of colour is due to the state of the iron which is less oxidised low down in the soil4 ,beneath the subsoil the soil grows #ch again coarser4 ,finally1 we recognise in it fragments of granite which ever grow larger as we descend1 till the soil has become replaced by the loose and shattered rock4 ,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 minerals4 ,the soil we have examined has plainly been derived in situ from the underlying rock4 ,it represents the more insoluble residue after water and acids have done their work4 ,each year there must be a very slow sinking of the surface1 but the ablation is infinitesimal4 ,the depth of such a soil may be considerable4 ,the total surface exposed by the countless grains of which it is composed is enormous4 ,in a cubic foot of average soil the surface area of the grains may be #ej1jjj square feet or more4 ,hence a soil only two feet deep may expose #ajj1jjj square feet for each square foot of surface area4 ,it is true that soils formed in this manner by atmospheric and organic actions take a very long time to grow4 ,it must be remembered1 however1 that the process is throughout attended by the removal in solution3 of chemically altered materials4 ,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 land1 that is1 #ci among the mountainous regions1 the feeding of the salts to the ocean arises from the slower work of meteorological and organic agencies attacking the molecular constitution of the rocks2 processes which best proceed where the drainage is sluggish and the quiescent conditions permit of the development of abundant organic growth and decay4 ,statistics of the solvent denudation of the continents support this view4 ,within recent years a very large amount of work has been expended on the chemical investigation of river waters of ,america and of ,europe4 ,f4 ,w4 ,clarke has1 at the expense of much labour1 collected and compared these results4 ,they are expressed as so many tonnes removed in solution per square mile per annum4 ,for ,north ,america the result shows #gi tonnes so removed2 for ,europe #ajj tonnes4 ,now there is a notable difference between the mean elevations of these two continents4 ,north ,america has a mean elevation of #gjj metres over sea level1 whereas the mean elevation of ,europe is but #cjj metres4 ,we see in these figures that the more mountainous land supplies less dissolved matter to the ocean than the land of lower elevation1 as our study has led us to expect4 ,we have now considered the source of the detrital sediments1 as well as of the dissolved matter which has given to the ocean1 in the course of geological time1 its present gigantic load of salts4 ,it is true there are further solvent and chemical effects exerted by the sea water #dj upon the sediments discharged into it2 but we are justified in concluding that1 relatively to the similar actions taking place in the soils1 the solvent and chemical work of the ocean is small4 ,the fact is1 the deposited detrital sediments around the continents occupy an area small when contrasted with the vast stretches of the land4 ,the area of deposition is much less than that of denudation2 probably hardly as much as one twentieth4 ,and1 again1 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 deposits4 ,the summation of the amounts of dissolved and detrital materials which denudation has brought into the ocean during the long denudative history of the ,earth1 as we might anticipate1 reveals quantities of almost unrealisable greatness4 ,the facts are among the most impressive which geological science has brought to light4 ,elsewhere in this volume they have been mentioned when discussing the age of the ,earth4 ,in the present connection1 however1 they are deserving of separate consideration4 ,the basis of our reasoning is that the ocean owes its saltness mainly if not entirely to the denudative activities we have been considering4 ,we must establish this4 ,we may1 in the first place1 say that any other view at once raises the greatest difficulties4 ,the chemical composition of the detrital sediments which are spread over #da the continents and which build up the mountains1 differs on the average very considerably from that of the igneous rocks4 ,we know the former have been derived from the latter1 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 rocks4 ,but the ocean alone can have received this dissolved matter4 ,we know of no other place in which to look for it4 ,it is true that some part of this dissolved matter has been again rejected by the ocean2 thus the formation of limestone is largely due to the abstraction of lime from sea water by organic and other agencies4 ,this1 however1 in no way relieves us of the necessity of tracing to the ocean the substances dissolved from the igneous rocks4 ,it follows that we have here a very causa for the saltness of the ocean4 ,the view that the ocean was salt from the first is without one known fact to support it1 and leaves us with the burden of the entire dissolved salts of geological time to dispose of--,where and how8 ,the argument we have outlined above becomes convincingly strong when examined more closely4 ,for this purpose we first compare the average chemical composition of the sedimentary and the igneous rocks4 ,the following table gives the percentages of the chief chemical constituents3 #a #a ,f4 ,w4 ,clarke3 ,a ,preliminary ,study of ,chemical ,denudation1 p4 #ac #db ,igneous4 ,sedimentary4 ,silica 7,si,o#b7 - #ei4ii #eh4ea ,alumina 7,al#b,o#c7 - #ae4jd #ac4jg ,ferric oxide 7,f#b,o#c7 - #b4ei #c4dj ,ferrous oxide 7,fe,o7 - #c4cd #b4jj ,magnesia 7,mg,o7 - #c4hi #b4eb ,lime 7,ca,o7 - #d4ha #e4db ,soda 7,na#b,o7 - #c4da #a4ab ,potash 7,k#b,o7 - #b4ie #b4hj ,water 7,h#b,o7 - #a4ib #d4bh ,carbon dioxide 7,,co#b7 - -- #d4ic ,minor constituents - #b4jf #a4ie #ajj4jj #ajj4jj ,in the derivation of the sediments from the igneous rocks there is a loss by solution of about #cc per cent2 i4e4 #ajj tons of igneous rock yields rather less than #gj tons of sedimentary rock4 ,this involves a concentration in the sediments of the more insoluble constituents4 ,to this rule the lime-content appears to be an exception4 ,it is not so in reality4 ,its high value in the sediments is due to its restoration from the ocean to the land4 ,the magnesia and potash are1 also1 largely restored from the ocean2 the former in dolomites and magnesian limestones2 the latter in glauconite sands4 ,the iron of the sediments shows increased oxidation4 ,the most notable difference in the two analyses appears1 however1 in the soda percentages4 ,this falls from #c4da in the igneous rock to #a4ab in the average sediment4 ,indeed1 this #dc 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 down4 ,to what is this so marked deficiency of soda to be ascribed8 ,it is a result of the extreme solubility of the salts of sodium in water4 ,this has not only rendered its deposition by evaporation a relatively rare and unimportant incident of geological history1 but also has protected it from abstraction from the ocean by organic agencies4 ,the element sodium has1 in fact1 accumulated in the ocean during the whole of geological time4 ,we can use the facts associated with the accumulation of sodium salts in the ocean as a means of obtaining additional support to the view1 that the processes of solvent denudation are responsible for the saltness of the ocean4 ,the new evidence may be stated as follows3 ,estimates of the amounts of sedimentary rock on the continents have repeatedly been made4 ,it is true that these estimates are no more than approximations4 ,but they undoubtedly are approximations1 and as such may legitimately be used in our argument2 more especially as final agreement tends to check and to support the several estimates which enter into them4 ,the most recent and probable estimates of the sediments on the land assign an average thickness of one mile of #dd secondary rocks over the land area of the world4 ,to this some increase must be made to allow for similar materials concealed in the ocean1 principally around the continental margins4 ,if we add #aj per cent4 and assign a specific gravity of #b4e we get as the mass of the sediments #fd x #ajaf tonnes4 ,but as this is about #fg per cent4 of the parent igneous rock--i4e4 the average igneous rock from which the sediments are derived--we conclude that the primary denuded rock amounted to a mass of about #ie x #ajaf tonnes4 ,now from the mean chemical composition of the secondary rocks we calculate that the mass of sediments as above determined contains #j4gb x#ajaf tonnes of the sodium oxide1 ,na#b,o4 ,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 therein1 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 it4 ,the mass of the ocean being well ascertained1 we easily calculate that the sodium in the ocean converted to sodium oxide amounts to #b4a x #ajaf tonnes4 ,hence between the estimated sediments and the waters of the ocean we can account for #b4hb x #ajaf tonnes of soda4 ,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 #c4j4 ,on the average analysis given above this should be #c4da per cent4 ,the agreement1 #de all things considered1 more especially the uncertainty in the estimate of the sediments1 is plainly in support of the view that oceanic salts are derived from the rocks2 if1 indeed1 it does not render it a certainty4 ,a leading and fundamental inference in the denudative history of the ,earth thus finds support3 indeed1 we may say1 verification4 ,in the light of this fact the whole work of denudation stands revealed4 ,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 ,earth4 ,geological history opened with the condensation of an atmosphere of immense extent1 which1 after long fluctuations between the states of steam and water1 finally settled upon the surface1 almost free of matter in solution3 an ocean of distilled water4 ,the epoch of denudation then began4 ,it will1 probably1 continue till the waters1 undergoing further loss of thermal energy1 suffer yet another change of state1 when their circulation will cease and their attack upon the rocks come to an end4 ,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 time4 ,from this the broad facts of the results of denudation admit of determination with considerable accuracy4 ,we can estimate the amount of rock which has been degraded by solvent and chemical actions1 and the amount of sediments which has been derived from it4 ,we are1 #df thus1 able to amend our estimate of the sediments which1 as determined by direct observation1 served to support the basis of our argument4 ,we now go straight to the ocean for the amount of sodium of denudative origin4 ,there may1 indeed1 have been some primitive sodium dissolved by a more rapid denudation while the ,earth's surface was still falling in temperature4 ,it can be shown1 however1 that this amount was relatively small4 ,neglecting it we may say with safety that the quantity of sodium carried into the ocean by the rivers must be between #ad1jjj and #ae1jjj million million tonnes3 i4e4 #ad1ejj x #ajab tonnes1 say4 ,keeping the figures to round numbers we find that this amount of sodium involves the denudation of about #hj x #ajaf tonnes of average igneous rock to #ec x #ajaf tonnes of average sediment4 ,from these vast quantities we know that the parent rock denuded during geological time amounted to some #cjj million cubic kilometres or about seventy million cubic miles4 ,the sediments derived therefrom possessed a bulk of #bbj million cubic kilometres or fifty million cubic miles4 ,the area of the land surface of the ,globe is #add million square kilometres4 ,the parent rock would have covered this to a uniform depth of rather more than two kilometres1 and the derived sediment to more than #a4e kilometres1 or about one mile deep4 ,the slow accomplishment of results so vast conveys some idea of the great duration of geological time4 #dg ,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 land1 but also as to the quantity which is spread over the floor of the ocean4 ,we see this when we follow the fate of the #cc per cent4 of dissolved salts which has been leached from the parent igneous rock1 and the mass of which we calculate from the ascertained mass of the latter1 to be #bg x #ajaf tonnes4 ,this quantity was at one time or another all in the ocean4 ,but1 as we saw above1 a certain part of it has been again abstracted from solution1 chiefly by organic agencies4 ,now the abstracted solids have not been altogether retained beneath the ocean4 ,movements of the land during geological time have resulted in some portion being uplifted along with other sediments4 ,these substances constitute1 mainly1 the limestones4 ,we see1 then1 that the #bg x #ajaf tonnes of substances leached from the parent igneous rocks have had a threefold destination4 ,one part is still in solution2 a second part has been precipitated to the bottom of the ocean2 a third part exists on the land in the form of calcareous rocks4 ,observation on the land sediments shows that the calcareous rocks amount to about #e per cent4 of the whole4 ,from this we find that #c x #ajaf tonnes1 approximately1 of such rocks have been taken from the ocean4 ,this accounts for one of the three classes of material #dh into which the original dissolved matter has been divided4 ,another of the three quantities is easily estimated3 the amount of matter still in solution in the ocean4 ,the volume of the ocean is #a1dad million cubic kilometres and its mass is #ade x #ajaf tonnes4 ,the dissolved salts in it constitute #c4d per cent4 of its mass2 or1 rather more than #e x #ajaf tonnes4 ,the limestones on the land and the salts in the sea water together make up about #h x #ajaf tonnes4 ,if we1 now1 deduct this from the total of #bg x #ajaf tonnes1 we find that about #ai x #ajaf tonnes must exist as precipitated matter on the floor of the ocean4 ,the area of the ocean is #cfg x #ajab square metres1 so that if the precipitated sediment possesses an average specific gravity of #b4e1 it would cover the entire floor to a uniform depth of #bah metres2 that is #gae feet4 ,this assumes that there was uniform deposition of the abstracted matter over the floor of the ocean4 ,of course1 this assumption is not justifiable4 ,it is certain that the rate of deposition on the floor of the sea has varied enormously with various conditions--principally with the depth4 ,again1 it must be remembered that this estimate takes no account of solid materials otherwise brought into the oceanic deposits2 e4g41 by wind-transported dust from the land or volcanic ejectamenta in the ocean depths4 ,it is not probable1 however1 that any considerable addition to the estimated mean depth of deposit from such sources would be allowable4 #di ,the greatness of the quantities involved in these determinations is almost awe inspiring4 ,take the case of the dissolved salts in the ocean4 ,they are but a fraction1 as we have seen1 of the total results of solvent denudation and represent the integration of the minute traces contributed by the river water4 ,yet the common salt 7chloride of sodium7 alone1 contained in the ocean1 would1 if abstracted and spread over the dry land as a layer of rock salt having a specific gravity of #b4b1 cover the whole to a depth of #ajg metres or #ced feet4 ,the total salts in solution in the ocean similarly spread over the land would increase the depth of the layer to #dfj feet4 ,after considering what this means we have to remember that this amount of matter now in solution in the seas is1 in point of fact1 less than a fifth part of the total dissolved from the rocks during geological time4 ,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 history4 ,the existing surface features of the earth must have been largely conditioned by the dynamical effects arising therefrom4 ,in dealing with the subject of mountain genesis we will1 elsewhere1 see that all the great mountain ranges have originated in the accumulation of the detrital sediments near the shore in areas which1 in consequence of the load1 gradually became depressed and developed into synclines of many thousands of feet in depth4 ,the most impressive surface features of the ,globe originated #ej in this manner4 ,we will see too that these events were of a rhythmic character2 the upraising of the mountains involving intensified mechanical denudation over the elevated area and in this way an accelerated transport of detritus to the sea2 the formation of fresh deposits2 renewed synclinal sinking of the sea floor1 and1 finally1 the upheaval of a younger mountain range4 ,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 ,earth4 ,the effects of purely solvent denudation are less easily traced1 but1 very probably1 they have been of not less importance4 ,i refer here to the transport from the land to the sea of matter in solution4 ,solvent denudation1 as observed above1 takes place mainly in the soils and in this way over the more level continental areas4 ,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 kilometre2 that is of more than #a1fjj feet of rock4 ,the continents have1 during geological time1 been lightened to this extent4 ,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 reached4 ,of this material the ocean #ea waters contain in solution an amount sufficient to increase their specific gravity by #b4g per cent4 ,taking the last point first1 it is interesting to note the effects upon the bulk of the ocean which has resulted from the matter dissolved in it4 ,from the known density of average sea water we find that #ajj ccs4 of it weigh just #ajb4g grammes4 ,of this #c4e per cent4 by weight are solids in solution4 ,that is to say1 #c4eid grammes4 ,hence the weight of water present is #ii4a grammes1 or a volume of #ii4a ccs4 ,from this we see that the salts present have increased the volume by #j4i ccs4 or #j4i per cent4 ,the average depth of the ocean is #b1jjj fathoms or #c1gjj metres4 ,the increase of depth due to salts dissolved in the ocean has been1 therefore1 #ajh feet or #cc4bd metres4 ,this result assumes that there has been no increased elastic compression due to the increased pressure1 and no change of compressional elastic properties4 ,we may be sure that the rise on the shore line of the land has not been less than #ajj feet4 ,we see then that as the result of solvent denudation we have to do with a heavier and a deeper ocean1 expanded in volume by nearly one per cent4 and the floor of which has become raised1 on an average1 about #gjj feet by precipitated sediment4 ,one of the first conceptions1 which the student of geology has to dismiss from his mind1 is that of the immobility or rigidity of the ,earth's crust4 ,the lane1 we live on sways even to the gentle rise and fail of ocean tides #eb around the coasts4 ,it suffers its own tidal oscillations due to the moon's attractions4 ,large tracts of semi-liquid matter underlie it4 ,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 gravity4 ,this state of equilibrium1 which was first recognised by ,pratt1 as part of the dynamics of the ,earth's crust1 has been named isostasy4 ,the state of the crust is that of mobile equilibrium4 ,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 ocean1 must all along have been attended by isostatic readjustment4 ,we cannot take any other view4 ,on the one hand the land was being lightened2 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 ocean4 ,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 #b1jjj feet above sea level4 ,we have seen that solvent denudation removed over #a1fjj feet of rock4 ,but we have no evidence that on the whole the elevation of land in the past was ever very different from what it now is4 ,we have1 then1 presented to our view the remarkable fact that throughout the past1 and acting with extreme #ec slowness1 the land has steadily been melted down into the sea and as steadily been upraised from the waters4 ,it is possible that the increased bulk of the ocean has led to a certain diminution of the exposed land area4 ,the point is a difficult one4 ,one thing we may without much risk assume4 ,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 areas2 the heated viscous materials creeping from depths far beneath the ocean floor to depths beneath the roots of the mountains which arose around the oceans4 ,such movements took ages for their accomplishment4 ,indeed1 they have been1 probably1 continuous all along and are still proceeding4 ,a low degree of viscosity will suffice to permit of movements so slow4 ,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 materials4 ,the whole sequence of movements presents an extraordinary picture of pseudo-vitality--reminding us of the circulatory and respiratory systems of a vast organism4 ,all great results in our universe are founded in motions and forces the most minute4 ,in contemplating the ,cause or the ,effect we stand equally impressed with the spectacle presented to us4 ,we shall now turn from the great effects of denudation upon the history and evolution of a world and consider for a moment activities #ed so minute in detail that their operations will probably for ever elude our bodily senses1 but which nevertheless have necessarily affected and modified the great results we have been considering4 ,the ocean a little way from the land is generally so free from suspended sediments that it has a blackness as of ink4 ,this blackness is due to its absolute freedom from particles reflecting the sun's light4 ,the beautiful blue of the ,swiss and ,italian lakes is due to the presence of very fine particles carried into them by the rivers2 the finest flour of the glaciers1 which remain almost indefinitely suspended in the water4 ,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 land1 that the presence of silt is to be observed4 ,the beautiful phenomenon of the coal-black sea is familiar to every yachtsman who has sailed to the west of our ,islands4#a ,there is1 in fact1 a very remarkable difference in the manner of settlement of fine sediments in salt and in fresh water4 ,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 investigation4 #a ,see ,tyndall's ,voyage to ,algeria in ,fragments of ,science4 ,the cause of the blue colour of the lakes has been discussed by various observers1 not always with agreement4 #ee ,it is easy to observe in the laboratory the fact of the different behaviour of salt and fresh water towards finely divided substances4 ,the nature of the insoluble substance is not important4 ,we place1 in a good light1 two glass vessels of equal dimensions2 the one filled with sea water1 the other with fresh water4 ,into each we stir the same weight of very finely powdered slate3 just so much as will produce a cloudiness4 ,in a few hours we find the sea water limpid4 ,the fresh water is still cloudy1 however2 and1 indeed1 may be hardly different in appearance from what it was at starting4 ,in itself this is a most extraordinary experiment4 ,we would have anticipated quite the opposite result owing to the greater density of the sea water4 ,but a still more interesting experiment remains to be carried out4 ,in the sea water we have many different salts in solution4 ,let us see if these salts are equally responsible for the result we have obtained4 ,for this purpose we measure out quantities of sodium chloride and magnesium chloride in the proportion in which they exist in sea water3 that is about as seven to one4 ,we add such an equal amount of water to each as represents the dilution of these salts in sea water4 ,then finally we stir a little of the finely powdered slate into each4 ,it will be found that the magnesium chloride1 although so much more dilute than the sodium chloride1 is considerably more active in clearing out the suspension4 ,we may now try such marine salts as magnesium sulphate1 #ef or calcium sulphate against sodium chloride2 keeping the marine proportions4 ,again we find that the magnesium and calcium salts are the most effective1 although so much more dilute than the sodium salt4 ,there is no visible clue to the explanation of these results4 ,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 sediment4 ,for only by the gathering of the particles together in little aggregates can we explain their rapid fall to the bottom4 ,it is not a question of viscosity 7i4e4 of resistance to the motion of the particles71 for the salt solutions are rather more viscous than the fresh water4 ,still more remarkable is the fact that every dissolved substance will not bring about the result4 ,thus if we dissolve sugar in water we find that1 if anything1 the silt settles more slowly in the sugar solution than in fresh water4 ,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 sugar4 ,the water is rendered a conductor of electricity4 ,long ago ,faraday explained this as due to the presence of free atoms of the dissolved salt in the solution1 carrying electric charges4 ,we now speak of the salt as ionised4 ,that is it is partly split up into ions or free electrified atoms of chlorine1 sodium1 magnesium1 etc41 according to the particular salt in solution4 ,this fact leads us to think that these electrified #eg atoms moving about in the solution may be the cause of the clumping or flocculation4 ,such electrified atoms are absent from the sugar solution3 sugar does not become ionised when it is dissolved4 ,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 chloride4 ,in each of the solutions of these substances there are free chlorine atoms each of which carries a single charge of negative electricity4 ,as these atoms are alike in both solutions the different behaviour of the solutions cannot be due to the chlorine4 ,but the metallic atom is very different in the two cases4 ,the ionised sodium atom is known to be monad or carries but one positive charge2 whereas the magnesium atom is diad and carries two positive charges4 ,if1 then1 we assume that the metallic1 positively electrified atom is in each case responsible1 we have something to go on4 ,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 valency2 that is with the number of unit charges associated with it4 ,thus diads such as magnesium1 calcium1 barium1 etc41 are very much more efficient than monads such as sodium1 potassium1 etc41 and again1 triads such as aluminium are1 similarly1 very much more powerful than diad atoms4 ,here1 in short1 we have arrived at the active cause of the phenomenon4 ,its inner mechanism #eh is1 however1 harder to fathom4 ,a plausible explanation can be offered1 but a study of it would take us too far4 ,sufficient has been said to show the very subtile nature of the forces at work4 ,we have here an effect due to the sea salts derived by denudation from the land which has been slowly augmenting during geological time4 ,it is certain that the ocean was practically fresh water in remote ages4 ,during those times the silt from the great rivers would have been carried very far from the land4 ,a ,mississippi of those ages would have sent its finer suspensions far abroad on a contemporary ,gulf stream3 not improbably right across the ,atlantic4 ,the earlier sediments of argillaceous type were not collected in the geosynclines and the genesis of the mountains was delayed proportionately4 ,but it was1 probably1 not for very long that such conditions prevailed4 ,for the accumulation of calcium salts must have been rapid1 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 mountain4 #ei ,,the ,,abundance ,,of ,,life #a ,,we had reached the ,pass of ,tre ,croci#b;and from a point a little below the summit1 looked eastward over the glorious ,val ,buona4 ,the pines which clothed the floor and lower slopes of the valley1 extended their multitudes into the furthest distance1 among the many recesses of the mountains1 and into the confluent ,val di ,misurina4 ,in the sunshine the ,alpine butterflies flitted from stone to stone4 ,the ground at our feet and everywhere throughout the forests teamed with the countless millions of the small black ants4 ,it was a magnificent display of vitality2 of the aggressiveness of vitality1 assailing the barren heights of the limestone1 wringing a subsistence from dead things4 ,and the question suggested itself with new force3 why the abundance of life and its unending activity8 ,in trying to answer this question1 the present sketch originated4 ,i propose to refer for an answer to dynamic considerations4 ,it is apparent that natural selection can only be concerned in a secondary way4 ,natural selection defines #a ,proc4 ,roy4 ,dublin ,soc41 vol4 vii41 #ahij4 #b ,in the ,dolomites of ,southeast ,tyrol2 during the summer of #ahij4 ,much of what follows was evolved in discussion with my fellow-traveller1 ,henry ,h4 ,dixon4 ,much of it is his4 #fj a certain course of development for the organism2 but very evidently some property of inherent progressiveness in the organism must be involved4 ,the mineral is not affected by natural selection to enter on a course of continual variation and multiplication4 ,the dynamic relations of the organism with the environment are evidently very different from those of inanimate nature4 ,,general ,,dynamic ,,conditions ,,attending ,,inanimate ,,actions ,it is necessary1 in the first place1 to refer briefly to the phenomena attending the transfer of energy within and into inanimate material systems4 ,it is not assumed here that these phenomena are restricted in their sphere of action to inanimate nature4 ,it is1 in fact1 very certain that they are not2 but while they confer on dead nature its own dynamic tendencies1 it will appear that their effects are by various means evaded in living nature4 ,we1 therefore1 treat of them as characteristic of inanimate actions4 ,we accept as fundamental to all the considerations which follow the truth of the principle of the ,conservation of ,energy4#a #a ,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 spent4--,clerk ,maxwell1 ,nature1 vol4 xix41 p4 #adb4 ,see also ,helmholtz ,on the ,conservation of ,force4 #fa ,whatever speculations may be made as to the course of events very distant from us in space1 it appears certain that dissipation of energy is at present actively progressing throughout our sphere of observation in inanimate nature4 ,it follows1 in fact1 from the second law of thermodynamics1 that whenever work is derived from heat1 a certain quantity of heat falls in potential without doing work or1 in short1 is dissipated4 ,on the other hand1 work may be entirely converted into heat4 ,the result is the heat-tendency of the universe4 ,heat1 being an undirected form of energy1 seeks1 as it were1 its own level1 so that the result of this heat-tendency is continual approach to uniformity of potential4 ,the heat-tendency of the universe is also revealed in the far-reaching law of maximum work1 which defines that chemical change1 accomplished without the intervention of external energy1 tends to the production of the body1 or system of bodies1 which disengage the greatest quantity of heat4#a ,and1 again1 vast numbers of actions going on throughout nature are attended by dissipatory thermal effects1 as those arising from the motions of proximate molecules 7friction1 viscosity71 and from the fall of electrical potential4 ,thus1 on all sides1 the energy which was once most probably existent in the form of gravitational potential1 is being dissipated into unavailable forms4 ,we must #a ,berthelot1 ,essai de ,mcanique ,chimique4 #fb recognize dissipation as an inevitable attendant on inanimate transfer of energy4 ,but when we come to consider inanimate actions in relation to time1 or time-rate of change1 we find a new feature in the phenomena attending transfer of energy2 a feature which is really involved in general statements as to the laws of physical interactions4#a ,it is seen1 that the attitude of inanimate material systems is very generally1 if not in all cases1 retardative of change--opposing it by effects generated by the primary action1 which may be called secondary for convenience4 ,further1 it will be seen that these secondary effects are those concerned in bringing about the inevitable dissipation4 ,as example1 let us endeavour to transfer gravitational potential energy contained in a mass raised above the surface of the ,earth into an elastic body1 which we can put into compression by resting the weight upon it4 ,in this way work is done against elastic force and stored as elastic potential energy4 ,we may deal with a metal spring1 or with a mass of gas contained in a cylinder fitted with a piston upon which the weight may be placed4 ,in either case we find the effect of compression is to raise the temperature of the substance1 thus causing its #a ,helmholtz1 ,ice and ,glaciers4 ,atkinson's collection of his ,popular ,lectures4 ,first ,series1 p4#abj4 ,quoted by ,tate1 ,heat1 p4 #caa4 #fc expansion or increased resistance to the descent of the weight4 ,and this resistance continues1 with diminishing intensity1 till all the heat generated is dissipated into the surrounding medium4 ,the secondary effect thus delays the final transfer of energy4 ,again1 if we suppose the gas in the cylinder replaced by a vapour in a state of saturation1 the effect of increased pressure1 as of a weight placed upon the piston1 is to reduce the vapour to a liquid1 thereby bringing about a great diminution of volume and proportional loss of gravitational potential by the weight4 ,but this change will by no means be brought about instantaneously4 ,when a little of the vapour is condensed1 this portion parts with latent heat of vaporisation1 increasing the tension of the remainder1 or raising its point of saturation1 so that before the weight descends any further1 this heat has to escape from the cylinder4 ,many more such cases might be cited4 ,the heating of india-rubber when expanded1 its cooling when compressed1 is a remarkable one2 for at first sight it appears as if this must render it exceptional to the general law1 most substances exhibiting the opposite thermal effects when stressed4 ,however1 here1 too1 the action of the stress is opposed by the secondary effects developed in the substance2 for it is found that this substance contracts when heated1 expands when cooled4 ,again1 ice being a substance which contracts in melting1 the effect of pressure is to facilitate melting1 lowering its freezing point4 ,but #fd so soon as a little melting occurs1 the resulting liquid calls on the residual ice for an amount of heat equivalent to the latent heat of liquefaction1 and so by cooling the whole1 retards the change4 ,such particular cases illustrate a principle controlling the interaction of matter and energy which seems universal in application save when evaded1 as we shall see1 by the ingenuity of life4 ,this principle is not only revealed in the researches of the laboratory2 it is manifest in the history of worlds and solar systems4 ,thus1 consider the effects arising from the aggregation of matter in space under the influence of the mutual attraction of the particles4 ,the tendency here is loss of gravitational potential4 ,the final approach is however retarded by the temperature1 or vis viva of the parts attending collision and compression4 ,from this cause the great suns of space radiate for ages before the final loss of potential is attained4 ,clerk ,maxwell#a 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 such4 ,from this if we assume the external forces acting upon a system not to rise above a certain potential 7which is the order of nature71 the constraints of secondary actions may1 under certain circumstances1 lead to final rejection of some of the energy1 or1 in any #a ,theory of ,heat1 p4 #aca4 #fe case1 to retardation of change in the system--dissipation of energy being the result4#a ,as such constraints seem inherently present in the properties of matter1 we may summarise as follows3 ,the transfer of energy into any inanimate material system is attended by effects retardative to the transfer and conducive to dissipation4 ,was this the only possible dynamic order ruling in material systems it is quite certain the myriads of ants and pines never could have been1 except all generated by creative act at vast primary expenditure of energy4 ,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 dissipation4 ,once created1 indeed1 it is conceivable that1 as heat engines1 they might have dragged out an existence of alternate life and death2 life in the hours of sunshine1 death in hours of darkness3 no final death1 however1 their lot1 till their parts were simply worn out by long use1 never made good by repair4 ,but the sustained and increasing activity of organized nature is a fact2 therefore some other order of events must be possible4 #a ,the law of ,least ,action1 which has been applied1 not alone in optics1 but in many mechanical systems1 appears physically based upon the restraint and retardation opposing the transfer of energy in material systems4 #ff ,,general ,,dynamic ,,conditions ,,attending ,,animate ,,actions ,what is the actual dynamic attitude of the primary organic engine--the vegetable organism8 ,we consider1 here1 in the first place1 not intervening1 but resulting phenomena4 ,the young leaf exposed to solar radiation is small at first1 and the quantity of radiant energy it receives in unit of time cannot exceed that which falls upon its surface4 ,but what is the effect of this energy8 ,not to produce a retardative reaction1 but an accelerative response3 for1 in the enlarging of the leaf by growth1 the plant opens for itself new channels of supply4 ,if we refer to the living protoplasm which1 with its unknown molecular arrangement1 is the only absolute test of the cell and of the organism in general1#a we find a similar attitude towards external sources of available energy4 ,in the act of growth increased rate of assimilation is involved1 so that there is an acceleration of change till a bulk of maximum activity is attained4 ,the surface1 finally1 becomes too small for the absorption of energy adequate to sustain further increase of mass 7,spencer#b71 and the acceleration ceases4 ,the waste going on in the central parts is then just balanced by the renewal at the surface4 ,by division1 by spreading of the mass1 by #a ,claus1 ,zoology1 p4 #ac4 #b ,geddes and ,thomson1 ,the ,evolution of ,sex1 p4 #bbj4 #fg out-flowing processes1 the normal activity of growth may be restored4 ,till this moment nothing would be gained by any of these changes4 ,one or other of them is now conducive to progressive absorption of energy by the organism1 and one or other occurs1 most generally the best of them1 subdivision4 ,two units now exist2 the total mass immediately on division is unaltered1 but paths for the more abundant absorption of energy are laid open4 ,the encystment of the protoplasm 7occurring under conditions upon which naturalists do not seem agreed#a7 is to all appearance protective from an unfavourable environment1 but it is often a period of internal change as well1 resulting in a segregation within the mass of numerous small units1 followed by a breakup of the whole into these units4 ,it is thus an extension of the basis of supply1 and in an impoverished medium1 where unit of surface is less active1 is evidently the best means of preserving a condition of progress4 ,thus1 in the organism which forms the basis of all modes of life1 a definite law of action is obeyed under various circumstances of reaction with the available energy of its environment4 ,similarly1 in the case of the more complex leaf1 we see1 not only in the phenomenon of growth1 but in its extension in a flattened form1 and in the orientation of greatest surface towards the source of energy1 an attitude towards #a ,however1 ,in no way comparable with death4 ,weismann1 ,biological ,memoirs1 p4 #aeh4 #fh available energy causative of accelerated transfer4 ,there is seemingly a principle at work1 leading to the increase of organic activity4 ,many other examples might be adduced4 ,the gastrula stage in the development of embryos1 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 labour2 the provision of cilia for drawing upon the energy supplies of the medium2 and more generally the specialisation of organs in the higher developments of life1 may alike be regarded as efforts of the organism directed to the absorption of energy4 ,when any particular organ becomes unavailing in the obtainment of supplies1 the organ in the course of time becomes aborted or disappears4#a ,on the other hand1 when a too ready and liberal supply renders exertion and specialisation unnecessary1 a similar abortion of functionless organs takes place4 ,this is seen in the degraded members of certain parasites4 ,during certain epochs of geological history1 the vegetable world developed enormously2 in response probably to liberal supplies of carbon dioxide4 ,a structural adaptation to the rich atmosphere occurred1 such as was calculated to cooperate in rapidly consuming the supplies1 and to this obedience to a law of progressive transfer of energy we owe the vast stores of energy now accumulated #a ,claus1 ,zoology1 p4 #aeg #fi in our coal fields4 ,and when1 further1 we reflect that this store of energy had long since been dissipated into space but for the intervention of the organism1 we see definitely another factor in organic transfer of energy--a factor acting conservatively of energy1 or antagonistically to dissipation4 ,the tendency of organized nature in the presence of unlimited supplies is to run riot4 ,this seems so universal a relation1 that we are safe in seeing here cause and effect1 and in drawing our conclusions as to the attitude of the organism towards available energy4 ,new species1 when they come on the field of geological history1 armed with fresh adaptations1 irresistible till the slow defences of the subjected organisms are completed1 attain enormous sizes under the stimulus of abundant supply1 till finally1 the environment1 living and dead1 reacts upon them with restraining influence4 ,the exuberance of the organism in presence of energy is often so abundant as to lead by deprivation to its self-destruction4 ,thus the growth of bacteria is often controlled by their own waste products4 ,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 system4 ,finally1 we are conscious in ourselves how1 by use1 our faculties are developed2 and it is apparent that all such progressive developments must rest on actions which respond to supplies with fresh demands4 ,possibly in the present and ever- #gj increasing consumption of inanimate power by civilised races1 we see revealed the dynamic attitude of the organism working through thought-processes4 ,whether this be so or not1 we find generally in organised nature causes at work which in some way lead to a progressive transfer of energy into the organic system4 ,and we notice1 too1 that all is not spent1 but both immediately in the growth of the individual1 and ultimately in the multiplication of the species1 there are actions associated with vitality which retard the dissipation of energy4 ,we proceed to state the dynamical principles involved in these manifestations1 which appear characteristic of the organism1 as follows3-- ,the transfer of energy into any animate material system is attended by effects conducive to the transfer1 and retardative of dissipation4 ,this statement is1 ,i think1 perfectly general4 ,it has been in part advanced before1 but from the organic more than the physical point of view4 ,thus1 hunger is an essential characteristic of living matter2 and again1 hunger is a dominant characteristic of living matter1#a are1 in part1 expressions of the statement4 ,if it be objected against the generality of the statement1 that there are periods in the life of individuals when stagnation and decay make their appearance1 we may answer1 that #a ,evolution of ,sex4 ,geddes and ,thomson1 chap4 xvi4 ,see also a reference to ,cope's theory of ,growth ,force1 in ,wallace's ,darwinism1 p4 #dbe4 #ga such phenomena arise in phases of life developed under conditions of external constraint1 as will be urged more fully further on1 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 ,earth4 ,the law of the unconstrained cell is growth on an ever increasing scale2 and although we assume the organic configuration1 whether somatic or reproductive1 to be essentially unstable1 so that continual inflow of energy is required merely to keep it in existence1 this does not vitiate the fact that1 when free of all external constraint1 growth gains on waste4 ,indeed1 even in the case of old age1 the statement remains essentially true1 for the phenomena then displayed point to a breakdown of the functioning power of the cell1 an approximation to configurations incapable of assimilation4 ,it is not as if life showed in these phenomena that its conditions could obtain in the midst of abundance1 and yet its law be suspended2 but as if they represented a degradation of the very conditions of life1 a break up1 under the laws of the inanimate1 of the animate contrivance2 so that energy is no longer available to it1 or the primary condition1 the transfer of energy into the animate system1 is imperfectly obeyed4 ,it is to the perfect contrivance of life our statement refers4 ,that the final end of all will be general non-availability there seems little reason to doubt1 and the organism1 itself dependent upon differences of potential1 cannot #gb hope to carry on aggregation of energy beyond the period when differences of potential are not4 ,the organism is not accountable for this4 ,it is being affected by events external to it1 by the actions going on through inanimate agents4 ,and although there be only a part of the received energy preserved1 there is a part preserved1 and this amount is continually on the increase4 ,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 ,earth1 is the result1 although a small one1 of energy reaching the ,earth since a remote period1 and which otherwise had been dissipated in space4 ,in inanimate actions throughout nature1 as we know it1 the availability is continually diminishing4 ,the change is all the one way4 ,as1 however1 the supply of available energy in the universe is 7probably7 limited in amount1 we must look upon the two as simply effecting the final dissipation of potential in very different ways4 ,the animate system is aggressive on the energy available to it1 spends with economy1 and invests at interest till death finally deprives it of all4 ,it has heirs1 indeed1 who inherit some of its gains1 but they1 too1 must die1 and ultimately there will be no successors1 and the greater part must melt away as if it had never been4 ,the inanimate system responds to the forces imposed upon it by sluggish changes2 of that which is thrust upon it1 it squanders uselessly4 ,the path of the energy is very different in the two cases4 #gc ,while it is true generally that both systems ultimately result in the dissipation of energy to uniform potential1 the organism can1 as we have seen1 under particular circumstances evade the final doom altogether4 ,it can lay up a store of potential energy which may be permanent4 ,thus1 so long as there is free oxygen in the universe1 our coalfields might1 at any time in the remote future1 generate light and heat in the universal grave4 ,it is necessary to observe on the fundamental distinction between the growth of the protoplasm and the growth of the crystal4 ,it is common to draw comparison between the two1 and to point to metabolism as the chief distinction4 ,but while this is the most obvious distinction the more fundamental one remains in the energy relations of the two with the environment4#a ,the growth of the crystal is the result of loss of energy2 that of the organism the result of gain of energy4 ,the crystal represents a last position of stable equilibrium assumed by molecules upon a certain loss of kinetic energy1 and the formation of the crystal by evaporation and concentration of a liquid does not1 in its dynamic aspect1 differ much from the precipitation of an amorphous sediment4 ,the organism1 on the other hand1 represents a more or less unstable condition formed and maintained by inflow of energy2 its formation1 indeed1 often attended with a loss of kinetic energy 7fixation of carbon in plants71 but1 if so1 accompanied by #a ,it appears exceptional for the crystal line configuration to stand higher in the scale of energy than the amorphous4 #gd a more than compensatory increase of potential molecular energy4 ,thus1 between growth in the living world and growth in the dead world1 the energy relations with the environment reveal a marked contrast4 ,again1 in the phenomena of combustion1 there are certain superficial resemblances which have led to comparison between the two4 ,here again1 however1 the attitudes towards the energy of the environment stand very much as and -4 ,the life absorbs1 stores1 and spends with economy4 ,the flame only recklessly spends4 ,the property of storage by the organism calls out a further distinction between the course of the two processes4 ,it secures that the chemical activity of the organism can be propagated in a medium in which the supply of energy is discontinuous or localised4 ,the chemical activity of the combustion can1 strictly speaking1 only be propagated among contiguous particles4 ,i need not dwell on the latter fact2 an example of the former is seen in the action of the roots of plants1 which will often traverse a barren place or circumvent an obstacle in their search for energy4 ,in this manner roots will find out spots of rich nutriment4 ,thus there is a dynamic distinction between the progress of the organism and the progress of the combustion1 or of the chemical reaction generally4 ,and although there be unstable chemical systems which absorb energy during reaction1 these are 7dynamically7 no more than the expansion of the compressed gas4 ,there is a certain #ge initial capacity in the system for a given quantity of energy2 this satisfied1 progress ceases4 ,the progress of the organism in time is continual1 and goes on from less to greater so long as its development is unconstrained and the supply of energy is unlimited4 ,we must regard the organism as a configuration which is so contrived as to evade the tendency of the universal laws of nature4 ,except we are prepared to believe that a violation of the second law of thermodynamics occurs in the organism1 that a sorting demon is at work within it1 we must1 ,i think1 assume that the interactions going on among its molecules are accompanied by retardation and dissipation like the rest of nature4 ,that such conditions are not incompatible with the definition of the dynamic attitude of the organism1 can be shown by analogy with our inanimate machines which1 by aid of hypotheses in keeping with the second law of thermodynamics1 may be supposed to fulfil the energy-functions of the plant or animal1 and1 in fact1 in all apparent respects conform to the definition of the organism4 ,we may assume this accomplished by a contrivance of the nature of a steam-engine1 driven by solar energy4 ,it has a boiler1 which we may suppose fed by the action of the engine4 ,it has piston1 cranks1 and other movable parts1 all subject to resistance from friction1 etc4 ,now there is no reason why this engine should not expend its surplus energy in shaping1 fitting1 and starting into action other engines3--in fact1 in reproductive sacrifice4 ,all #gf these other engines represent a multiplied absorption of energy as the effects of the energy received by the parent engine1 and may in time be supposed to reproduce themselves4 ,further1 we may suppose the parent engine to be small and capable of developing very little power1 but the whole series as increasing in power at each generation4 ,thus the primary energy relations of the vegetable organism are represented in these engines1 and no violation of the second law of thermodynamics involved4 ,we might extend the analogy1 and assuming these engines to spend a portion of their surplus energy in doing work against chemical forces--as1 for example1 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 engines1 representing the graminivorous animal4 ,it is obvious without proceeding to a tertiary or carnivorous order1 that the condition of energy in the animal world may be supposed fulfilled in these successive series of engines1 and no violation of the principles governing the actions going on in our machines assumed4 ,organisms evolving on similar principles would experience loss at every transfer4 ,thus only a portion of the radiant energy absorbed by the leaf would be expended in actual work1 chemical and gravitational1 etc4 ,it is very certain that this is1 in fact1 what takes place4 ,it is1 perhaps1 worth passing observation that1 from the nutritive dependence of the animal upon the vegetable1 #gg and the fact that a conversion of the energy of the one to the purposes of the other cannot occur without loss1 the mean energy absorbed daily by the vegetable for the purpose of growth must greatly exceed that used in animal growth2 so that the chemical potential energy of vegetation upon the earth is much greater than the energy of all kinds represented in the animal configurations4#a ,it appears1 too1 that in the power possessed by the vegetable of remaining comparatively inactive1 of surviving hard times by the expenditure and absorption of but little1 the vegetable constitutes a veritable reservoir for the uniform supply of the more unstable and active animal4 ,finally1 on the question of the manner of origin of organic systems1 it is to be observed that1 while the life of the present is very surely the survival of the fittest of the tendencies and chances of the past1 yet1 in the initiation of the organised world1 a single chance may have decided a whole course of events3 for1 once originated1 its own law secures its increase1 although within the new order of actions1 the law of the fittest must assert itself4 ,that such a progressive material system as an organism was possible1 and at some remote period was initiated1 is matter of knowledge2 whether or not the initiatory living configuration was rare and fortuitous1 or the probable result of the general action of physical laws acting among innumerable chances1 must remain matter of #a ,i find a similar conclusion arrived at in ,semper's ,animal ,life1 p4 #eb4 #gh speculation4 ,in the event of the former being the truth1 it is evidently possible1 in spite of a large finite number of habitable worlds1 that life is non-existent elsewhere4 ,if the latter is the truth1 it is almost certain that there is life in all1 or many of those worlds4 ,,evolution ,,and ,,acceleration ,,of ,,activity ,the primary factor in evolution is the struggle for existence4 ,this involves a natural selection among the many variations of the organism4 ,if we seek the underlying causes of the struggle1 we find that the necessity of food and 7in a lesser degree7 the desire for a mate are the principal causes of contention4 ,the former is much the more important factor1 and1 accordingly1 we find the greater degree of specialisation based upon it4 ,the present view assumes a dynamic necessity for its demands involved in the nature of the organism as such4 ,this assumption is based on observation of the outcome of its unconstrained growth1 reproduction1 and life-acts4 ,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 machines1 which assertion1 also1 is based on observation of results4 ,thus we pass from the superficial statements that organisms require food in order to live1 or that organisms desire food1 to the more fundamental one that3 ,the organism is a configuration of matter which absorbs energy acceleratively1 without limit1 when unconstrained4 #gi ,this is the dynamic basis for a struggle for existence4 ,the organism being a material system responding to accession of energy with fresh demands1 and energy being limited in amount1 the struggle follows as a necessity4 ,thus1 evolution guiding' the steps of the energy-seeking organism1 must presuppose and find its origin in that inherent property of the organism which determines its attitude in presence of available energy4 ,turning to the factor1 adaptation1 we find that this also must presuppose1 in order to be explicable1 some quality of aggressiveness on the part of the organism4 ,for adaptation in this or that direction is the result of repulse or victory1 and1 therefore1 we must presuppose an attack4 ,the attack is made by the organism in obedience to its law of demand2 we see in the adaptation of the organism but the accumulated wisdom derived from past defeats and victories4 ,where the environment is active1 that is living1 adaptation occurs on both sides4 ,improved means of defence or improved means of attack1 both presuppose activity4 ,thus the reactions to the environment1 animate and inanimate1 are at once the outcome of the eternal aggressiveness of the organism1 and the source of fresh aggressiveness upon the resources of the medium4 ,as concerns the survival of the fittest 7or natural selection71 we can1 ,i think1 at once conclude that the organism which best fulfils the organic law under the circumstances of supply is the fittest1 ipso facto4 ,in many #hj cases this is contained in the commonsense consideration1 that to be strong1 consistent with concealment from enemies which are stronger1 is best1 as giving the organism mastery over foes which are weaker1 and generally renders it better able to secure supplies4 ,weismann points out that natural selection favours early and abundant reproduction4 ,but whether the qualifications of the fittest be strength1 fertility1 cunning1 fleetness1 imitation1 or concealment1 we are safe in concluding that growth and reproduction must be the primary qualities which at once determine selection and are fostered by it4 ,inherent in the nature of the organism is accelerated absorption of energy1 but the qualifications of the fittest are various1 for the supply of energy is limited1 and there are many competitors for it4 ,to secure that none be wasted is ultimately the object of natural selection1 deciding among the eager competitors what is best for each4 ,in short1 the facts and generalisations concerning evolution must presuppose an organism endowed with the quality of progressive absorption of energy1 and retentive of it4 ,the continuity of organic activity in a world where supplies are intermittent is evidently only possible upon the latter condition4 ,thus it appears that the dynamic attitude of the organism1 considered in these pages1 occupies a fundamental position regarding its evolution4 ,we turn to the consideration of old age and death1 endeavouring to discover in what relation they stand to the innate progressiveness of the organism4 #ha ,,the ,,periodicity ,,of ,,the ,,organism ,,and ,,the ,,law ,,of ,,progressive ,,activity ,the organic system is essentially unstable4 ,its aggressive attitude is involved in the phenomenon of growth1 and in reproduction which is a form of growth4 ,but the energy absorbed is not only spent in growth4 ,it partly goes1 also1 to make good the decay which arises from the instability of the organic unit4 ,the cell is molecularly perishable4 ,it possesses its entity much as a top keeps erect1 by the continual inflow of energy4 ,metabolism is always taking place within it4 ,any other condition would1 probably1 involve the difficulties of perpetual motion4 ,the phenomenon of old age is not evident in the case of the unicellular organism reproducing by fission4 ,at any stage of its history all the individuals are of the same age3 all contain a like portion of the original cell1 so far as this can be regarded as persisting where there is continual flux of matter and energy4 ,in the higher organisms death is universally evident4 ,why is this8 ,the question is one of great complexity4 ,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 mortality4 ,for it is to this phenomenon--that of cell division--that the continued life of the protozoon is to be ascribed1 as we have already seen4 ,reproduction is1 in fact1 the saving factor here4 ,as we do not know the source or nature of the stimulus #hb responsible for cell division we cannot give a molecular account of death in the higher organisms4 ,however we shall now see that1 philosophically1 we are entitled to consider reproduction as a saving factor in this case also2 and to regard the death of the individual much as we regard the fall of the leaf from the tree3 i4e4 as the cessation of an outgrowth from a development extending from the past into the future4 ,the phenomena of old age and natural death are1 in short1 not at variance with the progressive activity of the organism4 ,we perceive this when we come to consider death from the evolutionary point of view4 ,professor ,weismann1 in his two essays1 ,the ,duration of ,life1 and ,life and ,death1#a adopts and defends the view that death is not a primary necessity but that it has been secondarily acquired by adaptation4 ,the cell was not inherently limited in its number of cell-generations4 ,the low unicellular organisms are potentially immortal1 the higher multicellular forms with well-differentiated organs contain the germs of death within themselves4 ,he finds the necessity of death in its utility to the species4 ,long life is a useless luxury4 ,early and abundant reproduction is best for the species4 ,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 sound4 ,hence natural selection will shorten life4 #a ,see his ,biological ,memoirs4 ,oxford1 #ahhh4 #hc ,weismann contends against the transmission of acquired characters as being unproved4#a ,he bases the appearance of death on variations in the reproductive cells1 encouraged by the ceaseless action of natural selection1 which led to a differentiation into perishable somatic cells and immortal reproductive cells4 ,the time-limit of any particular organism ultimately depends upon the number of somatic cell-generations and the duration of each generation4 ,these quantities are predestined in the germ itself which gives rise to each individual4 ,the existence of immortal metazoan organisms is conceivable1 but their capacity for existence is influenced by conditions of the external world2 this renders necessary the process of adaptation4 ,in fact1 in the differentiation of somatic from reproductive cells1 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 species4 ,the soma is in a sense a secondary appendage of the real bearer of life--the reproductive cells4 ,the somatic cells probably lost their immortal qualities1 on this immortality becoming useless to the species4 ,their mortality may have been a mere consequence of their differentiation 7loc4 cit41 p4 #adj71 itself due to natural selection4 ,natural death was not1 in fact1 introduced from absolute intrinsic necessity inherent in the nature of living matter1 but on grounds of utility1 #a ,biological ,memoirs1 p4 #adb4 #hd that is from necessities which sprang up1 not from the general conditions of life1 but from those special conditions which dominate the life of multicellular organisms4 ,on the inherent immortality of life1 ,weismann finally states3 ,reproduction is1 in truth1 an essential attribute of living matter1 just as the growth which gives rise to it4444 ,life is continuous1 and not periodically interrupted3 ever since its first appearance upon the ,earth in the lowest organism1 it has continued without break2 the forms in which it is manifest have alone undergone change4 ,every individual alive today--even the highest--is to be derived in an unbroken line from the first and lowest forms4 #a ,at the present day the view is very prevalent that the soma of higher organisms is1 in a sense1 but the carrier for a period of the immortal reproductive cells 7,ray ,lankester7#b--;an appendage due to adaptation1 concerned in their supply1 protection1 and transmission4 ,and whether we regard the time-limit of its functions as due to external constraints1 recurrently acting till their effects become hereditary1 or to variations more directly of internal origin1 encouraged by natural selection1 we see in old age and death phenomena ultimately brought about in obedience to the action of an environment4 ,these are not inherent in the properties of living matter4 ,but1 in spite #a ,loc4 cit41 p4 #aei #b ,geddes and ,thomson1 ,the ,evolution of ,sex1 chap4 xviii4 #he of its mortality1 the body remains a striking manifestation of the progressiveness of the organism1 for to this it must be ascribed4 ,to it energy is available which is denied to the protozoon4 ,ingenious adaptations to environment are more especially its privilege4 ,a higher manifestation1 however1 was possible1 and was found in the development of mind4 ,this1 too1 is a servant of the cell1 as the genii of the lamp4 ,through it energy is available which is denied to the body4 ,this is the masterpiece of the cell4 ,its activity dates1 as it were1 but from yesterday1 and today it inherits the most diverse energies of the ,earth4 ,taking this view of organic succession1 we may liken the individual to a particle vibrating for a moment and then coming to rest1 but sweeping out in its motion one wave in the continuous organic vibration travelling from the past into the future4 ,but as this vibration is one spreading with increased energy from each vibrating particle1 its propagation involves a continual accelerated inflow of energy from the surrounding medium1 a dynamic condition unknown in periodic effects transmitted by inanimate actions1 and1 indeed1 marking the fundamental difference between the dynamic attitudes of the animate and inanimate4 ,we can trace the periodic succession of individuals on a diagram of activity with some advantage4 ,considering1 first1 the case of the unicellular organism reproducing by subdivision and recalling that conditions1 definite and inevitable1 oppose a limit to the rate of growth1 or1 for our #hf present purpose1 rate of consumption of energy1 we proceed as follows3 ,fig4 #a ,along a horizontal axis units of time are measured2 along a vertical axis units of energy4 ,then the life-history of the amoeba1 for example1 appears as a line such as ,a in ,fig4 #a4 ,during the earlier stages of its growth the rate of absorption of energy is small2 so that in the unit interval of time1 t1 the small quantity of energy1 e#a1 is absorbed4 ,as life advances1 the activity of the organism augments1 till finally this rate attains a maximum1 when e#b units of energy are consumed in the unit of time4#a #a ,reference to p4 #gf1 where the organic system is treated as purely mechanical1 may help readers to understand what is involved in this curve4 ,the solar engine may1 unquestionably1 have its activity defined by such a curve4 ,the organism is1 indeed1 more complex2 but neither this fact nor our ignorance of its mechanism1 affects the principles which justify the diagram4 #hg ,on this diagram reproduction1 on the part of the organism1 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 latter1 when the rate of consumption of energy has become constant4 ,the organism ,a has now ceased to act as a unit4 ,the products of fission each carry on the vital development of ,fig4 #b the species along the curve ,b1 which may be numbered 7#b71 to signify that it represents the activity of two individuals1 and so on1 the numbering advancing in geometrical progression4 ,the particular curvature adopted in the diagram is1 of course1 imaginary2 but it is not of an indeterminate nature4 ,its course for any species is a characteristic of fundamental physical importance1 regarding the part played in nature by the particular organism4 #hh ,in ,fig4 #b is represented the path of a primitive multicellular organism before the effects of competition produced or fostered its mortality4 ,the lettering of ,fig4 #a applies2 the successive reproductive acts are marked ,p#a1 ,p#b2 ,q#a1 ,q#b1 etc41 in the paths of the successive individuals4 ,fig4 #c ,the next figure 7,fig4 #c7 diagrammatically illustrates death in organic history4 ,the path ever turns more and more from the axis of energy1 till at length the point is reached when no more energy is available2 a tangent to the curve at this point is at right angles to the axis of energy and parallel to the time axis4 ,the death point is reached1 and however great a length we measure along the axis of time1 no further consumption of energy is #hi indicated by the path of the organism4 ,drawing the line beyond the death point is meaningless for our present purpose4 ,it is observable that while the progress of animate nature finds its representation on this diagram by lines sloping upwards from left to right1 the course of events in inanimate nature--for example1 the history of the organic configuration after death1 or ,fig4 #d the changes progressing--let us say1 in the solar system1 or in the process of a crystallisation1 would appear as lines sloping downwards from left to right4 ,whatever our views on the origin of death may be1 we have to recognise a periodicity of functions in the life-history of the successive individuals of the present day2 and whether or not we trace this directly or indirectly to #ij a sort of interference with the rising wave of life1 imposed by the activity of a series of derived units1 each seeking energy1 and in virtue of its adaptation each being more fitted to obtain it than its predecessor1 or even leave the idea of interference out of account altogether in the origination or perpetuation of death1 the truth of the diagram 7,fig4 #d7 holds in so far as it may be supposed to graphically represent the dynamic history of the individual4 ,the point chosen on the curve for the origination of a derived unit is only applicable to certain organisms1 many reproducing at the very close of life4 ,a chain of units are supposed here represented4#a ,,the ,,length ,,of ,,life ,if we lay out waves as above to a common scale of time for different species1 the difference of longevity is shown in the greater or less number of vibrations executed in a given time1 i4e4 in greater or less frequency4 ,we cannot indeed draw the curvature correctly1 for this would necessitate a knowledge which we have not of the activity of the organism at different periods of its life-history1 and so neither can we plot the direction of the organic line of propagation with respect to the #a ,projecting upon the axes of time and energy any one complete vibration1 as in ,fig4 #d1 the total energy consumed by the organism during life is the length ,e on the axis of energy1 and its period of life is the length ,t on the time-axis4 ,the mean activity is the quotient ,e_/,t4 #ia axes of reference as this involves a knowledge of the mean activity4#a ,the group of curves which follow1 relating to typical animals possessing very different activities 7,fig4 #e71 are therefore entirely diagrammatic1 except in respect to the approximate ,fig4 #e longevity of the organisms4 7#a7 might represent an animal of the length of life and of the activity of ,man2 7#b71 on the same scale of longevity1 #a ,in the relative food-supply at various periods of life the curvature is approximately determinable4 #ib one of the smaller mammals2 and 7#c71 the life-history of a cold blooded animal living to a great age2 e4g4 certain of the reptilia4 ,it is probable1 that to conditions of structural development1 under the influence of natural selection1 the question of longer or shorter life is in a great degree referable4 ,thus1 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 procurable1 whatever we may assume as to the strength or cunning exerted by the individual in its efforts to obtain its supplies4 ,on the other hand1 development along lines of small growth1 in that reproduction is less costly1 will probably lead to increased rate of reproduction4 ,it is1 in fact1 matter of general observation that in the case of larger animals the rate of reproduction is generally slower than in the case of smaller animals4 ,but the rate of reproduction might be expected to have an important influence in determining the particular periodicity of the organism4 ,were we to depict in the last diagram1 on the same time-scale as ,man1 the vibrations of the smaller and shorter-lived living things1 we would see but a straight line1 save for secular variations in activity1 representing the progress of the species in time3 the tiny thrills of its units lost in comparison with the yet brief period of ,man4 ,the interdependence of the rate of reproduction and #ic the duration of the individual is1 indeed1 very probably revealed in the fact that short-lived animals most generally reproduce themselves rapidly and in great abundance1 and vice versa4 ,in many cases where this appears contradicted1 it will be found that the young are exposed to such dangers that but few survive 7e4g4 many of the reptilia1 etc471 and so the rate of reproduction is actually slow4 ,death through the periodic rigour of the inanimate environment calls forth phenomena very different from death introduced or favoured by competition4 ,a multiplicity of effects simulative of death occur4 ,organisms will1 for example1 learn to meet very rigorous conditions if slowly introduced1 and not permanent4 ,a transitory period of want can be tided over by contrivance4 ,the lily withdrawing its vital forces into the bulb1 protected from the greatest extremity of rigour by seclusion in the ,earth2 the trance of the hibernating animal2 are instances of such contrivances4 ,but there are organisms whose life-wave truly takes up the periodicity of the ,earth in its orbit4 ,thus the smaller animals and plants1 possessing less resources in themselves1 die at the approach of winter1 propagating themselves by units which1 whether egg or seed1 undergo a period of quiescence during the season of want4 ,in these quiescent units the energy of the organism is potential1 and the time-energy function is in abeyance4 ,this condition is1 perhaps1 foreshadowed in the encyst- #id ment of the amoeba in resistance to drought4 ,in most cases of hibernation the time-energy function seems maintained at a loss of potential by the organism1 a diminished vital consumption of energy being carried on at the expense of the stored energy of the tissues4 ,so1 too1 even among the largest organisms there will be a diminution of activity periodically inspired by climatological conditions4 ,thus1 wholly or in part1 the activity of organisms is recurrently affected by the great energy--tides set up by the ,earth's orbital motion4 ,fig4 #f ,similarly in the phenomenon of sleep the organism responds to the ,earth's axial periodicity1 for in the interval of night a period of impoverishment has to be endured4 ,thus the diurnal waves of energy also meet a response in the organism4 ,these tides and waves of activity would appear as larger and smaller ripples #ie on the life-curve of the organism4 ,but in some1 in which life and death are encompassed in a day1 this would not be so2 and for the annual among plants1 the seed rest divides the waves with lines of no activity 7,fig4 #f74 ,thus1 finally1 we regard the organism as a dynamic phenomenon passing through periodic variations of intensity4 ,the material systems concerned in the transfer of the energy rise1 flourish1 and fall in endless succession1 like cities of ancient dynasties4 ,at points of similar phase upon the waves the rate of consumption of energy is approximately the same2 the functions1 too1 which demand and expend the energy are of similar nature4 ,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 conclusion4 ,in the life of the individual rhythmic dynamic phenomena reappear which in some cases have no longer a parallel in the external world1 or under conditions when the individual is no longer influenced by these external conditions411 ,in many cases the periodic phenomena ultimately die out under new influences1 like the oscillations of a body in a viscous medium2 in others when they seem to be more deeply rooted in physiological conditions they persist4 ,the length of life is dependent upon the number #a ,the ,descent of ,man4 #if of generations of somatic cells which can succeed one another in the course of a single life1 and furthermore the number as well as the duration of each single cell-generation is predestined in the germ itself4#a ,only in the vague conception of a harmonising or formative structural influence derived from the germ1 perishing in each cell from internal causes1 but handed from cell to cell till the formative influence itself degrades into molecular discords1 does it seem possible to form any physical representation of the successive events of life4 ,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 nature4 ,thus1 ultimately1 to the waste within the cell1 to the presence of a force retardative of its perpetual harmonic motions1 the death of the individual is to be ascribed4 ,perhaps in protoplasmic waste the existence of a universal death should be recognised4 ,it is here we seem to touch inanimate nature2 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 participates4#b #a ,weismann1 ,life and ,death2 ,biological ,memoirs1 p4 #adf4 #b ,in connection with the predestinating power and possible complexity of the germ1 it is instructive to reflect on the very great molecular population of even the smallest spores--giving rise to very simple forms4 ,thus1 the spores of the unicellular ,schizomycetes are estimated to dimensions as low as #a_/aj1jjj of a millimetre in diameter 7,cornil et ,babes1 ,les ,batteries1 #a4 #cg74 ,from ,lord ,kelvin's estimate of the number of molecules in water1 comprised within the length of a wave-length of yellow light 7,the ,size of ,atoms1 ,proc4 ,r4 ,i41 vol4 x41 p4 #ahe7 it is probable that such spores contain some #ejj1jjj molecules1 while one hundred molecules range along a diameter4 #ig ,,the ,,numerical ,,abundance ,,of ,,life ,we began by seeking in various manifestations of life a dynamic principle sufficiently comprehensive to embrace its very various phenomena4 ,this1 to all appearance1 found1 we have been led to regard life1 to a great extent1 as a periodic dynamic phenomenon4 ,fundamentally1 in that characteristic of the contrivance1 which leads it to respond favourably to transfer of energy1 its enormous extension is due4 ,it is probable that to its instability its numerical abundance is to be traced--for this1 necessitating the continual supply of all the parts already formed1 renders large1 undifferentiated growth1 incompatible with the limited supplies of the environment4 ,these are fundamental conditions of abundant life upon the ,earth4 ,although we recognise in the instability of living systems the underlying reason for their numerical abundance1 secondary evolutionary causes are at work4 ,the most important of these is the self-favouring nature of the phenomenon of reproduction4 ,thus there is a tendency not only to favour reproductiveness1 but early reproductiveness1 in the form of one prolific reproductive4 #ih act1 after which the individual dies4#a ,hence the wavelength of the species diminishes1 reproduction is more frequent1 and correspondingly greater numbers come and go in an interval of time4 ,another cause of the numerical abundance of life exists1 as already stated1 in the conditions of nourishment4 ,energy is more readily conveyed to the various parts of the smaller mass1 and hence the lesser organisms will more actively functionate2 and this1 as being the urging dynamic attitude1 as well as that most generally favourable in the struggle1 will multiply and favour such forms of life4 ,on the other hand1 however1 these forms will have less resource within themselves1 and less power of endurance1 so that they are only suitable to fairly uniform conditions of supply2 they cannot survive the long continued want of winter1 and so we have the seasonal abundance of summer4 ,only the larger and more resistant organisms1 whether animal or vegetable1 will1 in general1 populate the ,earth from year to year4 ,from this we may conclude that1 but for the seasonal energy-tides1 the development of life upon the globe had gone along very different lines from those actually followed4 ,it is1 indeed1 possible that the evolution of the larger organisms would not have occurred2 there would have been no vacant place for their development1 and a being so endowed as ,man could hardly #a ,weismann1 ,the ,duration of ,life4 #ii have been evolved4 ,we may1 too1 apply this reasoning elsewhere1 and regard as highly probable1 that in worlds which are without seasonal influences1 the higher developments of life have not appeared2 except they have been evolved under other conditions1 when they might for a period persist4 ,we have1 indeed1 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 organisms4 ,it appears that to the dynamic attitude of life in the first place1 and secondarily to the environmental conditions limiting undifferentiated growth1 as well as to the action of heredity in transmitting the reproductive qualities of the parent to the offspring1 the multitudes of the pines1 and the hosts of ants1 are to be ascribed4 ,other causes are very certainly at work1 but these1 ,i think1 must remain primary causes4 ,we well know that the abundance of the ants and pines is not a tithe of the abundance around us visible and invisible4 ,it is a vain endeavour to realise the countless numbers of our fellow-citizens upon the ,earth2 but1 for our purpose1 the restless ants1 and the pines solemnly quiet in the sunshine1 have served as types of animate things4 ,in the pine the gates of the organic have been thrown open that the vivifying river of energy may flow in4 ,the ants and the butterflies sip for a brief moment of its waters1 and again vanish into the #ajj inorganic3 life1 love and death encompassed in a day4 ,whether the organism stands at rest and life comes to it on the material currents of the winds and waters1 or in the vibratory energy of the ther2 or1 again1 whether with restless craving it hurries hither and thither in search of it1 matters nothing4 ,the one principle--the accelerative law which is the law of the organic--urges all alike onward to development1 reproduction and death4 ,but although the individual dies death is not the end2 for life is a rhythmic phenomenon4 ,through the passing ages the waves of life persist3 waves which change in their form and in the frequency to which they are attuned from one geologic period to the next1 but which still ever persist and still ever increase4 ,and in the end the organism outlasts the generations of the hills4 #aja ,,the ,,bright ,,colours ,,of ,,alpine ,,flowers #a ,,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 valleys4 ,that this is actually the case1 and not merely an effect produced upon the observer by the scant foliage rendering the bloom more conspicuous1 has been shown by comparative microscopic examination of the petals of species growing on the heights and in the valleys4 ,such examination has revealed that in many cases pigment granules are more numerous in the individuals growing at the higher altitudes4 ,the difference is specially marked in ,myosotis sylvatica1 ,campanula rotundifolia1 ,ranunculus sylvaticus1 ,galium cruciatum1 and others4 ,it is less marked in the case of ,thymus serpyllum and ,geranium sylvaticum2 while in ,rosa alpina and ,erigeron alpinus no difference is observable4#b ,in the following cases a difference of intensity of colour is1 according to ,kerner 7,pflanzenleben1 #aa4 #ejd71 especially noticeable3-- ,agrostemma githago1 ,campanula #a ,proc4 ,royal ,dublin ,society1 #ahic4 #b ,g4 ,bonnier1 quoted by ,de ,varigny1 ,experimental ,evolution1 p4 #ee4 #ajb pusilla1 ,dianthus inodorus 7silvestris71 ,gypsophila repens1 ,lotus corniculatus1 ,saponaria ocymoides1 ,satureja hortensis1 ,taraxacumm officinale1 ,vicia cracca1 and ,vicia sepium4 ,to my own observation this beautiful phenomenon has always appeared most obvious and impressive4 ,it appears to have struck many unprofessional observers4 ,helmholtz offers the explanation that the vivid colours are the result of the brighter sunlight of the heights4 ,it has been said1 too1 that they are the direct chemical effects of a more highly ozonized atmosphere4 ,the latter explanation ,i am unable to refer to its author4 ,the following pages contain a suggestion on the matter1 which occurred to me while touring1 along with ,henry ,h4 ,dixon1 in the ,linthal district of ,switzerland last summer4#a ,if the bloom of these higher alpine flowers is especially pleasing to our own sthetic instincts1 and markedly conspicuous to us as observers1 why not also especially attractive and conspicuous to the insect whose mission it is to wander from flower to flower over the pastures8 ,the answer to this question involves the hypothesis ,i would advance as accounting for the bright colours of high-growing individuals4 ,in short1 ,i believe a satisfactory explanation is to be found in the conditions of insect life in the higher alps4 ,in the higher pastures the summer begins late and #a ,the summer of #ahib4 #ajc closes early1 and even in the middle of summer the day closes in with extreme cold1 and the cold of night is only dispelled when the sun is well up4 ,again1 clouds cover the heights when all is clear below1 and cold winds sweep over them when there is warmth and shelter in the valleys4 ,with these rigorous conditions the pollinating insects have to contend in their search for food1 and that when the rival attractions of the valleys below are so many4 ,i believe it is these rigorous conditions which are indirectly responsible for the bright colours of alpine flowers4 ,for such conditions will bring about a comparative scarcity of insect activity on the heights2 and a scarcity or uncertainty in the action of insect agency in effecting fertilization will intensify the competition to attract attention1 and only the brightest blooms will be fertilized4#a ,this will be a natural selection of the brightest1 or the #a ,grant ,allen1 ,i have recently learned1 advances in ,science in ,arcady the theory that there is a natural selective cause fostering the bright blooms of alpines4 ,the selective cause is1 however1 by him referred to the greater abundance of butterfly relatively to bee fertilizers4 ,the former1 he says1 display more sthetic instinct than bees4 ,in the valley the bees secure the fertilization of all4 ,i may observe that upon the ,fridolins ,alp all the fertilizers we observed were bees4 ,i have always found butterflies very scarce at altitudes of #g1jjj to #h1jjj feet4 ,the alpine bees are very light in body1 like our hive bee1 and ,i do not think rarefaction of the atmosphere can operate to hinder its ascent to the heights1 as ,grant ,allen suggests4 ,the observations on the death-rate of bees and butterflies on the glacier1 to be referred to presently1 seem to negative such a hypothesis1 and to show that a large preponderance of bees over butterflies make their way to the heights4 #ajd brightest will be the fittest1 and this condition1 along with the influence of heredity1 will encourage a race of vivid flowers4 ,on the other hand1 the more scant and uncertain root supply1 and the severe atmospheric conditions1 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 sthetic one of colour and brightness between flower and flower4 ,hence the scant foliage and vivid bloom would be at once the result of a necessary economy1 and a resort to the best method of securing reproduction under the circumstances of insect fertilizing agency4 ,or1 in other words1 while the luxuriant growth is forbidden by the conditions1 and thus methods of offence and defence1 based upon vigorous development1 reduced in importance1 it would appear that the struggle is mainly referred to rivalry for insect preference4 ,it is probable that this is the more economical manner of carrying on the contest4 ,in the valleys we see on every side the struggle between the vegetative organs of the plant2 the soundless battle among the leaves and branches4 ,the blossom here is carried aloft on a slender stem1 or else1 taking but a secondary part in the contest1 it is relegated to obscurity 7,p#a4 ,,xii474 ,further up on the mountains1 where the conditions are more severe and the supplies less abundant1 the leaf and branch assume lesser dimensions1 for they are costly weapons to provide and the elements are unfriendly #aje to their existence 7,pl4 ,,xiii474 ,still higher1 approaching the climatic limit of vegetable life1 the struggle for existence is mainly carried on by the sthetic rivalry of lowly but conspicuous blossoms4 ,as regards the conditions of insect life in the higher alps1 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 time4 ,it appears as if at the approach of dusk these are attracted by the gleam of the snow1 and quitting the pastures1 lose themselves upon the glaciers and firns1 there to die in hundreds4 ,thus in an ascent of the ,tdi from the ,fridolinshte we counted in the early dawn sixty-seven frozen bees1 twenty-nine dead butterflies1 and some half-dozen moths on the ,biferten ,glacier and ,firn4 ,these numbers1 it is to be remembered1 only included those lying to either side of our way over the snow1 so that the number must have mounted up to thousands when integrated over the entire glacier and firn4 ,approaching the summit none were found4 ,the bees resembled our hive bee in appearance1 the butterflies resembled the small white variety common in our gardens1 which has yellow and black upon its wings4 ,one large moth1 striped across the abdomen1 and measuring nearly two inches in length of body1 was found4 ,upon our return1 long after the sun's rays had grown strong1 we observed some of the butterflies showed signs of reanimation4 ,we descended so quickly to avoid the inconvenience of the soft snow that we had time for no #ajf close observation on the frozen bees4 ,but dead bees are common objects upon the snows of the alps4 ,these remarks ,i noted down roughly while at ,linthal last summer1 but quite recently ,i read in ,natural ,science#a the following note3 ,late ,flowering ,plants4--,while we write1 the ivy is in flower1 and bees1 wasps1 and flies are jostling each other and struggling to find standing-room on the sweet-smelling plant4 ,how great must be the advantage obtained by this plant through its exceptional habit of flowering in the late autumn1 and ripening its fruit in the spring4 ,to anyone who has watched the struggle to approach the ivy-blossom at a time when nearly all other plants are bare1 it is evident that1 as far as transport of pollen and cross-fertilization go1 the plant could not flower at a more suitable time4 ,the season is so late that most other plants are out of flower1 but yet it is not too late for many insects to be brought out by each sunny day1 and each insect1 judging by its behaviour1 must be exceptionally hungry4 ,not only has the ivy the world to itself during its flowering season1 but it delays to ripen its seed till the spring1 a time when most other plants have shed their seed1 and most edible fruits have been picked by the birds4 ,thus birds wanting fruit in the spring can obtain little but ivy1 and how they appreciate the ivy berry is evident #a ,for ,december1 #ahib1 vol4 i41 p4 #gcj4 #ajg by the purple stains everywhere visible within a short distance of the bush4 ,these remarks suggest that the ivy adopts the converse attitude towards its visitors to that forced upon the alpine flower4 ,the ivy bloom is small and inconspicuous1 but then it has the season to itself1 and its inconspicuousness is no disadvantage1 i4e4 if one plant was more conspicuous than its neighbours1 it would not have any decided advantage where the pollinating insect is abundant and otherwise unprovided for4 ,its dark-green berries in spring1 which ,i would describe as very inconspicuous1 have a similar advantage in relation to the necessities of bird life4 ,the experiments of ,m4 ,c4 ,flahault must be noticed4 ,this naturalist grew seeds of coloured flowers which had ripened in ,paris1 part in ,upsala1 and part in ,paris2 and seed which had ripened in ,upsala1 part at ,paris1 and part at ,upsala4 ,the flowers opening in the more northern city were in most cases the brighter4#a ,if this observation may be considered indisputable1 as appears to be the case1 the question arises1 ,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 ,upsala8 ,if we suppose an affirmative answer1 the theory of direct effect by sun brightness must ,i think be abandoned4 ,but ,i venture to think that the explanation of the ,upsala #a ,quoted by ,de ,varigny1 ,experimental ,evolution1 p4 #ef4 #ajh experiment is not to be found in direct climatic influence upon the colour1 but in causes which lie deeper1 and involve some factors deducible from biological theory4 ,the organism1 as a result of the great facts of heredity and of the survival of the fittest1 is necessarily a system which gathers experience with successive generations2 and the principal lesson ever being impressed upon it by external events is economy4 ,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 gained4 ,with regard to using the passing opportunity the entire seasonal development of life is a manifestation of this attitude1 and the fleetness1 agility1 etc41 of higher organisms are developments in this direction4 ,the higher vegetable organism is not locomotory1 save in the transferences of pollen and seed1 for its food comes to it1 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 earth4 ,but1 even so1 the vegetable organism must stand ever ready and waiting for its supplies4 ,its molecular parts must be ready to seize the prey offered to it1 somewhat as the waiting spider the fly4 ,hence1 the plant stands ready2 and every cloud with moving shadow crossing the fields handicaps the shaded to the benefit of the unshaded plant in the adjoining field4 ,the open bloom #aji is a manifestation of the generally expectant attitude of the plant1 but in relation to reproduction4 ,as regards economy1 any principle of maximum economy1 where many functions have to be fulfilled1 will1 we may very safely predict1 involve as far as possible mutual helpfulness in the processes going on4 ,thus the process of the development towards meeting any particular external conditions1 ,a1 suppose1 will1 if possible1 tend to forward the development towards meeting conditions ,b2 so that1 in short1 where circumstances of morphology and physiology are favourable1 the ideally economical system will be attained when in place of two separate processes1 a1 1 the one process y1 cheaper than a 1 suffices to advance development simultaneously in both the directions ,a and ,b4 ,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 are4 ,such economy might be simply illustrated by considering the case of a reservoir of water elevated above two hydraulic motors1 so that the elevated mass of water possessed gravitational potential4 ,the available energy here represents the stored-up energy in the organism4 ,how best may the water be conveyed to the two motors the organic systems reacting towards conditions ,a and ,b so #aaj that as little energy as possible is lost in transit8 ,if the motors are near together it is most economical to use the one conduit1 which will distribute the requisite supply of water to both4 ,if the motors are located far asunder it will be most economical to lay separate conduits4 ,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 conditions4 ,but an important and obvious consequence arises in the supply of the two motors from the one conduit4 ,we cannot work one motor without working the other4 ,if we open a valve in the conduit both motors start into motion and begin consuming the energy stored in the tank4 ,and although they may both under one set of conditions be doing useful and necessary work1 in some other set of conditions it may be needless for both to be driven4 ,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 memory1#a ,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 past4 #a ,ewald ,hering1 quoted by ,ray ,lankaster1 ,the ,advancement of ,science1 p4 #bhc4 #aaa ,in short1 we may suppose the entire development of the plant1 towards meeting certain groups of external conditions1 physiologically knit together according as ,nature tends to associate certain groups of conditions4 ,thus1 in the case in point1 climatic rigour and scarcity of pollinating agency will ever be associated2 and in the long experience of the past the most economical physiological attitude towards both is1 we may suppose1 adopted2 so that the presence of one condition excites the apparent unconscious memory of the other4 ,in reality the process of meeting the one condition involves the process and development for meeting the other4 ,and this consideration may be extended very generally to such organisms as can survive under the same associated natural conditions1 for the history of evolution is so long1 and the power of locomotion so essential to the organism at some period in its life history1 that we cannot philosophically assume a local history for members of a species even if widely severed geographically at the present day4 ,at some period in the past then1 it is very possible that the individuals today thriving at ,paris1 acquired the experience called out at ,upsala4 ,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 ,paris2 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 animals4 ,but1 again1 possibly the experi- #aab ence was acquired far back in the evolutionary history of the flower4#a ,but a further consideration arises4 ,not only at each moment in the life of the individual must maximum income and most judicious expenditure be considered1 but in its whole life history1 and even over the history of its race1 the efficiency must tend to be a maximum4 ,this principle is even carried so far that when necessary it leads to the death of the individual1 as in the case of those organisms which1 having accomplished the reproductive act1 almost immediately expire4 ,this view of nature may be repellent1 but it is1 nevertheless1 evident that we are parts of a system which ruthlessly sacrifices the individual on general grounds of economy4 ,thus1 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 curve1 drawn below the axis along which time is measured1 representing the mean rate of expenditure of energy on development1 reproduction1 etc4 7,fig4 #g71 this latter curve1 which is1 of course1 #a ,the blooms of self-fertilising1 and especially of cleistogamic plants 7e4g4 ,viola71 are examples of unconscious memory1 or unconscious association of ideas leading to the development of organs now functionless4 ,the ,pontederia crassipes of the ,amazon1 which develops its floating bladders when grown in water1 but aborts them rapidly when grown on land1 and seems to retain this power of adaptation to the environment for an indefinite period of time1 must act in each case upon an unconscious memory based upon past experience4 ,many other cases might be cited4 #aac physiologically dependent on the former1 must be of such a nature from its origin to its completion in death1 that the condition is realized of the most economical rate of expenditure at each period of life4#a ,the rate of expenditure of energy at any period of life is1 of course1 in such a curve defined by the slope of the curve towards the axis of time at the period in question2 but this particular slope must be led to by a previous part of the curve1 and involves its past and future course to a very great extent4 ,fig4 #g ,there will1 therefore1 be impressed upon the organism by the factors of evolution a unified course of economical expenditure completed only by its death1 and which will give to the developmental progress of the individual its prophetic character4 ,in this way we look to the unified career of each organic unit1 from its commencement in the ovum to the day #a ,see ,the ,abundance of ,life4 #aad when it is done with vitality1 for that preparation for momentous organic events which is in progress throughout the entire course of development2 and to the economy involved in the welding of physiological processes for the phenomenon of physiological memory1 wherein we see reflected1 as it were1 in the development of the organism1 the association of inorganic restraints occurring in nature which at some previous period impressed itself upon the plastic organism4 ,we may picture the seedling at ,upsala1 swayed by organic memory and the inherited tendency to an economical preparation for future events1 gradually developing towards the sthetic climax of its career4 ,in some such manner only does it appear possible to account for the prophetic development of organisms1 not alone to be observed in the alpine flowers1 but throughout nature4 ,and thus1 finally1 to the effects of natural selection and to actions defined by general principles involved in biology1 ,i would refer for explanation of the manner in which flowers on the ,alps develop their peculiar beauty4 #aae ,,mountain ,,genesis ,,our ancestors regarded mountainous regions with feelings of horror1 mingled with commiseration for those whom an unkindly destiny had condemned to dwell therein4 ,we1 on the other hand1 find in the contemplation of the great alps of the ,earth such peaceful and elevated thoughts1 and such rest to our souls1 that it is to those very solitudes we turn to heal the wounds of ife4 ,it is difficult to explain the cause of this very different point of view4 ,it is probably1 in part1 to be referred to that cloud of superstitious horror which1 throughout the ,middle ,ages1 peopled the solitudes with unknown terrors2 and1 in part1 to the asceticism which led the pious to regard the beauty and joy of life as snares to the soul's well-being4 ,in those eternal solitudes where the overwhelming forces of ,nature are most in evidence1 an evil principle must dwell or a dragon's dreadful brood must find a home4 ,but while in our time the aesthetic aspect of the hills appeals to all1 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 genesis4 ,they lose a past history which for interest com- #aaf petes with anything science has to tell of the changes of the ,earth4 ,great as are the physical features of the mountains compared with the works of ,man1 and great as are the forces involved compared with those we can originate or control1 the loftiest ranges are small contrasted with the dimensions of the ,earth4 ,it is well to bear this in mind4 ,i give here 7,pl4 ,,xv47 a measured drawing showing a sector cut from a sphere of #ej cms4 radius2 so much of it as to exhibit the convergence of its radial boundaries which if prolonged will meet at the centre4 ,on the same scale as the radius the diagram shows the highest mountains and the deepest ocean4 ,the average height of the land and the average depth of the ocean are also exhibited4 ,we see how small a movement of the crust the loftiest elevation of the ,himalaya represents and what a little depression holds the ocean4 ,nevertheless1 it is not by any means easy to explain the genesis of those small elevations and depressions4 ,it would lead us far from our immediate subject to discuss the various theoretical views which have been advanced to account for the facts4 ,the idea that mountain folds1 and the lesser rugosities of the ,earth's surface1 arose in a wrinkling of the crust under the influence of cooling and skrinkage of the subcrustal materials1 is held by many eminent geologists1 but not without dissent from others4 ,the most striking observational fact connected with mountain structure is that1 without exception1 the ranges #aag of the ,earth are built essentially of sedimentary rocks3 that is of rocks which have been accumulated at some remote past time beneath the surface of the ocean4 ,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 position4 ,it is not uncommon to meet among unobservant people those who regard all mountain ranges as volcanic in origin4 ,volcanoes1 however1 do not build mountain ranges4 ,they break out as more or less isolated cones or hills4 ,compare the map of the ,auvergne with that of ,switzerland2 the volcanoes of ,south ,italy with the ,apennines4 ,such great ranges as those which border with triple walls the west coast of ,north ,america are in no sense volcanic3 nor are the ,pyrenees1 the ,caucasus1 or the ,himalaya4 ,volcanic materials are poured out from the summits of the ,andes1 but the range itself is built up of folded sediments on the same architecture as the other great ranges of the ,earth4 ,before attempting an explanation of the origin of the mountains we must first become more closely acquainted with the phenomena attending mountain elevation4 ,at the present day great accumulations of sediment are taking place along the margins of the continents where the rivers reach the ocean4 ,thus1 the ,gulf of ,mexico receiving the sediment of the ,mississippi and ,rio ,grande2 #aah the northeast coast of ,south ,america receiving the sediments of the ,amazons2 the east coast of ,asia receiving the detritus of the ,chinese rivers2 are instances of such areas of deposition4 ,year by year1 century by century1 the accumulation progresses1 and as it grows the floor of the sea sinks under the load4 ,of the yielding of the crust under the burthen of the sediments we are assured2 for otherwise the many miles of vertically piled strata which are uplifted to our view in the mountains1 never could have been deposited in the coastal seas of the past4 ,the flexure and sinking of the crust are undeniable realities4 ,such vast subsiding areas are known as geosynclines4 ,from the accumulated sediments of the geosynclines the mountain ranges of the past have in every case originated2 and the mountains of the future will assuredly arise and lofty ranges will stand where now the ocean waters close over the collecting sediments4 ,every mountain range upon the ,earth enforces the certainty of this prediction4 ,the mountain-forming movement takes place after a certain great depth of sediment is collected4 ,it is most intense where the thickness of deposit is greatest4 ,we see this when we examine the structure of our existing mountain ranges4 ,at either side where the sediments thin out1 the disturbance dies away1 till we find the comparatively shallow and undisturbed level sediments which clothe the continental surface4 ,whatever be the connection between the deposition and #aai the subsequent upheaval1 the element of great depth of accumulation seems a necessary condition and must evidently enter as a factor into the ,physical ,processes involved4 ,the mountain range can only arise where the geosyncline is deeply filled by long ages of sedimentation4 ,dana's description of the events attending mountain building is impressive3 ,a mountain range of the common type1 like that to which the ,appalachians belong1 is made out of the sedimentary formations of a long preceding era2 beds that were laid down conformably1 and in succession1 until they had reached the needed thickness2 beds spreading over a region tens of thousands of square miles in area4 ,the region over which sedimentary formations were in progress in order to make1 finally1 the ,appalachian range1 reached from ,new ,york to ,alabama1 and had a breadth of #ajj to #bjj miles1 and the pile of horizontal beds along the middle was #dj1jjj feet in depth4 ,the pile for the ,wahsatch ,mountains was #fj1jjj feet thick1 according to ,king4 ,the beds for the ,appalachians were not laid down in a deep ocean1 but in shallow waters1 where a gradual subsidence was in progress2 and they at last1 when ready for the genesis1 lay in a trough #dj1jjj feet deep1 filling the trough to the brim4 ,it thus appears that epochs of mountain-making have occurred only after long intervals of quiet in the history of a continent4#a #a ,dana1 ,manual of ,geology1 third edition1 p4 #gid #abj ,on the western side of ,north ,america the work of mountain-building was1 indeed1 on the grandest scale4 ,for long ages and through a succession of geological epochs1 sedimentation had proceeded so that the accumulations of ,palaeozoic and ,mesozoic times had collected in the geosyncline formed by their own ever increasing weight4 ,the site of the future ,laramide range was in late ,cretaceous times occupied by some #ej1jjj feet of sedimentary deposits2 but the limit had apparently been attained1 and at this time the ,laramide range1 as well as its southerly continuation into the ,united ,states1 the ,rockies1 had their beginning4 ,chamberlin and ,salisbury#a estimate that the height of the mountains developed in the ,laramide range at this time was #bj1jjj feet1 and that1 owing to the further elevation which has since taken place1 from #cb1jjj to #ce1jjj feet would be their present height if erosion had not reduced them4 ,thus on either side of the ,american continent we have the same forces at work1 throwing up mountain ridges where the sediments had formerly been shed into the ocean4 ,these great events are of a rhythmic character2 the crust1 as it were1 pulsating under the combined influences of sedimentation and denudation4 ,the first involves downward movements under a gathering load1 and ultimately a reversal of the movement to one of upheaval2 the second factor1 which throughout has been in #a ,chamberlin and ,salisbury1 ,geology1 #aijf1 iii41 #afc4 #aba operation as creator of the sediments1 then intervenes as an assailant of the newly-raised mountains1 transporting their materials again to the ocean1 when the rhythmic action is restored to its first phase1 and the age-long sequence of events must begin all over again4 ,it has long been inferred that compressive stress in the crust must be a primary condition of these movements4 ,the wvork required to effect the upheavals must be derived from some preexisting source of energy4 ,the phenomenon--intrinsically one of folding of the crust--suggests the adjustment of the earth-crust to a lessening radius2 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 phenomenon4 ,the compressive stresses must be confined to the upper few miles of the crust1 for1 in fact1 the downward increase of temperature and pressure soon confers fluid properties on the medium1 and slow tangential compression results in hydrostatic pressure rather than directed stresses4 ,thus the folding visible in the mountain range1 and the lateral compression arising therefrom1 are effects confined to the upper parts of the crust4 ,the energy which uplifts the mountain is probably a surviving part of the original gravitational potential energy of the crust itself4 ,it must be assumed that the crust in following downwards the shrinking subcrustal magma1 develops immense compressive stresses in #abb its materials1 vast geographical areas being involved4 ,when folding at length takes place along the axis of the elongated syncline of deposition1 the stresses find relief probably for some hundreds of miles1 and the region of folding now becomes compressed in a transverse direction4 ,as an illustration1 the ,laramide range1 according to ,dawson1 represents the reduction of a surface-belt #ej miles wide to one of #be miles4 ,the marvellous translatory movements of crustal folds from south to north arising in the genesis of the ,swiss ,alps1 which recent research has brought to light1 is another example of these movements of relief1 which continue to take place perhaps for many millions of years after they are initiated4 ,the result of this yielding of the crust is a buckling of the surface which on the whole is directed upwards2 but depression also is an attendant1 in many cases at least1 on mountain upheaval4 ,thus we find that the ocean floor is depressed into a syncline along the western coast of ,south ,america2 a trough always parallel to the ranges of the ,andes4 ,the downward deflection of the crust is of course an outcome of the same compressive stresses which elevate the mountain4 ,the fact that the yielding of the crust is always situated where the sediments have accumulated to the greatest depth1 has led to attempts from time to time of establishing a physical connexion between the one and the other4 ,the best-known of these theories is that of ,babbage and ,herschel4 ,this seeks the connexion in the rise of the #abc geotherms into the sinking mass of sediment and the consequent increase of temperature of the earth-crust beneath4 ,it will be understood that as these isogeotherms1 or levels at which the temperature is the same1 lie at a uniform distance from the surface all over the ,earth1 unless where special variations of conductivity may disturb them1 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 depressed4 ,in other words the geotherms rise into the sinking sediments1 always1 however1 preserving their former average distance from the surface4 ,the argument is that as this process undoubtedly involves the heating up of that portion of the crust which the sediments have displaced downwards1 the result must be a local enfeeblement of the crust1 and hence these areas become those of least resistance to the stresses in the crust4 ,when this theory is examined closely1 we see that it only amounts to saying that the bedded rocks1 which have taken the place of the igneous materials beneath1 as a part of the rigid crust of the ,earth1 must be less able to withstand compressive stress than the average crust4 ,for there has been no absolute rise of the geotherms1 the thermal conductivities of both classes of materials differing but little4 ,sedimentary rock has merely taken the place of average crust-rock1 and is subjected to the same average temperature and pressure prevailing in the surrounding crust4 ,but are there any grounds for the #abd assumption that the compressive resistance of a complex of sedimentary rocks is inferior to one of igneous materials8 ,the metamorphosed siliceous sediments are among the strongest rocks known as regards resistance to compressive stress2 and if limestones have indeed plastic qualities1 it must be remembered that their average amount is only some #e per cent4 of the whole4 ,again1 so far as rise of temperature in the upper crust may affect the question1 a temperature which will soften an average igneous rock will not soften a sedimentary rock1 for the reason that the effect of solvent denudation has been to remove those alkaline silicates which confer fusibility4 ,when1 however1 we take into account the radioactive content of the sediments the matter assumes a different aspect4 ,the facts as to the general distribution of radioactive substances at the surface1 and in rocks which have come from considerable depths in the crust1 lead us to regard as certain the widespread existence of heat-producing radioactive elements in the exterior crust of the ,earth4 ,we find1 indeed1 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 inwards4 ,and we conclude that there must be a thickness of crust amounting to some miles1 containing the radioactive elements4 ,some of the most recent measurements of the quantities of radium and thorium in the rocks of igneous origin--e4g4 granites1 syenites1 diorites1 basalts1 etc41 show that the #abe radioactive heat continually given out by such rocks amounts to about one millionth part of #j4f calories per second per cubic metre of average igneous rock4 ,as we have to account for the escape of about #j4jjad calorie#a per square metre of the ,earth's surface per second 7assuming the rise of temperature downwards1 i4e4 the gradient of temperature1 to be one degree centigrade in #ce metres7 the downward extension of such rocks might1 prima facie1 be as much as #ai kilometres4 ,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 down1 i4e4 that our experiments reveal the average radioactivity of a radioactive crust4 ,there is much to be said for this assumption4 ,the rocks which enter into the measurements come from all depths of the crust4 ,it is highly probable that the less silicious1 i4e4 the more basic1 rocks1 mainly come from considerable depths2 the more acid or silica-rich rocks1 from higher levels in the crust4 ,the radioactivity determined as the mean of the values for these two classes of rock closely agrees with that found for intermediate rocks1 or rocks containing an intermediate amount of silica4 ,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 us4 #a ,the calorie referred to is the quantity of heat required to heat one gram of water1 i4e4 one cubic centimetre of water--through one degree centigrade4 #abf ,it is therefore highly probable that the value found for the mean radioactivity of acid and basic rocks1 or that found for intermediate rocks1 truly represents the radioactive state of the crust to a considerable depth4 ,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 rock4 ,this appears in the failure of a radioactive layer1 taken at a thickness of about #ai-kilometres1 to account for the deep-seated high temperatures which we find to be indicated by volcanic phenomena at many places on the surface4 ,it is not hard to show that the #ai-kilometre layer would account for a temperature no higher than about #bgj ,c4 at its base4 ,it is true that this will be augmented beneath the sedimentary deposits as we shall presently see2 and that it is just in association with these deposits that deep-seated temperatures are most in evidence at the surface2 but still the result that the maximum temperature beneath the crust in general attains a value no higher than #bgj ,c4 is hardly tenable4 ,we conclude1 then1 that some other source of heat exists beneath4 ,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 crust4 ,or1 again1 the heat may be primeval or original heat1 still escaping from a cooling world4 ,for our present purpose it does not much matter which view #abg we adopt4 ,but we must recognise that the calculated depth of #ai kilometres of crust1 possessing the average radioactivity of the surface1 is excessive2 for1 in fact1 we are compelled by the facts to recognise that some other source of heat exists beneath4 ,if the observed surface gradient of temperature persisted uniformly downwards1 at some #ce kilometres beneath the surface there would exist temperatures 7of about #ajjj ,c47 adequate to soften basic rocks4 ,it is probable1 however1 that the gradient diminishes downwards1 and that the level at which such temperatures exist lies rather deeper than this4 ,it is1 doubtless1 somewhat variable according to local conditions2 nor can we at all approximate closely to an estimate of the depth at which the fusion temperatures will be reached1 for1 in fact1 the existence of the radioactive layer very much complicates our estimates4 ,in what follows we assume the depth of softening to lie at about #dj kilometres beneath the surface of the normal crust2 that is #be miles down4 ,it is to be observed that ,prestwich and other eminent geologists1 from a study of the facts of crust-folding1 etc41 have arrived at similar estimates4#a ,as a further assumption we are probably not far wrong if we assign to the radioactive part of this crust a thickness of about #aj or #ab kilometres2 i4e4 six or seven miles4 ,this is necessarily a rough approximation only2 but the conclusions at which #a ,prestwich1 ,proc4 ,royal ,soc41 xii41 p4 #aeh et seq4 #abh we shall arrive are reached in their essential features allowing a wide latitude in our choice of data4 ,we shall speak of this part of the crust as the normal radioactive layer4 ,an important fact is evolved from the mathematical investigation of the temperature conditions arising from the presence of such a radioactive layer4 ,it is found that the greatest temperature1 due to the radioactive heat everywhere evolved in the layer--i4e4 the temperature at its base--is proportional to the square of the thickness of the layer4 ,this fact has a direct bearing on the influence of radioactivity upon mountain elevation2 as we shall now find4 ,the normal radioactive layer of the ,earth is composed of rocks extending--as we assume--approximately to a depth of #ab kilometres 7#g4e miles74 ,the temperature at the base of this layer due to the heat being continually evolved in it1 is1 say1 t#a4 ,now1 let us suppose1 in the trough of the geosyncline1 and upon the top of the normal layer1 a deposit of1 say1 #aj kilometres 7#f4b miles7 of sediments is formed during a long period of continental denudation4 ,what is the effect of this on the temperature at the base of the normal layer depressed beneath this load8 ,the total thickness of radioactive rocks is now #bb kilometres4 ,accordingly we find the new temperature t#b1 by the proportion t#a 3 t#b 33 #ab 3 #bb ,that is1 as #add to #dhd4 ,in fact1 the temperature is more than trebled4 ,it is true we here assume the radioactivity of the sediments #abi and of the normal crust to be the same4 ,the sediments are1 however1 less radioactive in the proportion of #d to #c4 ,nevertheless the effects of the increased thickness will be considerable4 ,now this remarkable increase in the temperature arises entirely from the condition attending the radioactive heating2 and involves something additional to the temperature conditions determined by the mere depression and thickening of the crust as in the ,babbage-,herschel theory4 ,the latter theory only involves a shifting of the temperature levels 7or geotherms7 into the deposited materials4 ,the radioactive theory involves an actual rise in the temperature at any distance from the surface2 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 7,pl4 ,,xv1 p4 #aah74 ,in this manner the rigid part of the crust is reduced in thickness where the great sedimentary deposits have collected4 ,a ten-kilometre layer of sediment might result in reducing the effective thickness of the crust by #cj per cent42 a fourteen-kilometre layer might reduce it by nearly #ej per cent4 ,even a four-kilometre deposit might reduce the effective resistance of the crust to compressive forces1 by #aj per cent4 ,such results are1 of course1 approximate only4 ,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 #acj of the upper crust which is bearing the simultaneously increasing compressive stresses4 ,below this geotherm long-continued stress resolves itself into hydrostatic pressure2 above it 7there is1 of course1 no sharp line of demarcation7 the crust accumulates elastic energy4 ,the final yielding and flexure occur when the resistant cross-section has been sufficiently diminished4 ,it is probable that there is also some outward hydrostaitic thrust over the area of rising temperature1 which assists in determining the upward throw of the folds4 ,when yielding has begun in any geosyncline1 and the materials are faulted and overthrust1 there results a considerably increased thickness4 ,as an instance1 consider the piling up of sediments over the existing materials of the ,alps1 which resulted from the compressive force acting from south to north in the progress of ,alpine upheaval4 ,schmidt of ,basel has estimated that from #ae to #bj kilometres of rock covered the materials of the ,simplon as now exposed1 at the time when the orogenic forces were actively at work folding and shearing the beds1 and injecting into their folds the plastic gneisses coming from beneath4#a ,the lateral compression of the area of deposition of the ,laramide1 already referred to1 resulted in a great thickening of the deposits4 ,many other cases might be cited2 the effect is always in some degree necessarily produced4 #a ,schmidt1 ,ec4 ,geol4 ,helvelix1 vol4 ix41 ,no4 #d1 p4 #eij #aca ,if time be given for the heat to accumulate in the lower depths of the crushed-up sediments1 here is an additional source of increased temperature4 ,the piled-up masses of the ,simplon might have occasioned a rise due to radioactive heating of one or two hundred degrees1 or even more2 and if this be added to the interior heat1 a total of from #hjj to #ajjj might have prevailed in the rocks now exposed at the surface of the mountain4 ,even a lesser temperature1 accompanied by the intense pressure conditions1 might well occasion the appearances of thermal metamorphism described by ,weinschenk1 and for which1 otherwise1 there is difficulty in accounting4#a ,this increase upon the primarily developed temperature conditions takes place concurrently with the progress of compression2 and while it cannot be taken into account in estimating the conditions of initial yielding of the crust1 it adds an element of instability1 inasmuch as any progressive thickening by lateral compression results in an accelerated rise of the goetherms4 ,it is probable that time sufficient for these effects to develop1 if not to their final1 yet to a considerable extent1 is often available4 ,the viscous movements of siliceous materials1 and the out-pouring of igneous rocks which often attend mountain elevation1 would find an explanation in such temperatures4 #a ,weinschenk1 ,congrs ,gol4 ,internat41 #aijj1 i41 p4 #ccb4 #acb ,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 time1 and often shifting their position but little from the first scene of sedimentation1 becomes accounted for4 ,the source of thermal energy1 as we have already remarked1 is in fact transported with the sediments--that energy which determines the place of yielding and upheaval1 and ordains that the mountain ranges shall stand around the continental borders4 ,sedimentation from this point of view is a convection of energy4 ,when the consolidated sediments are by these and by succeeding movements forced upwards into mountains1 they are exposed to denudative effects greatly exceeding those which affect the plains4 ,witness the removal during late ,tertiary times of the vast thickness of rock enveloping the ,alps4 ,such great masses are hurried away by ice1 rivers1 and rain4 ,the ocean receives them2 and with infinite patience the world awaits the slow accumulation of the radioactive energy beginning afresh upon its work4 ,the time for such events appears to us immense1 for millions of years are required for the sediments to grow in thickness1 and the geotherms to move upwards2 but vast as it is1 it is but a moment in the life of the parent radioactive substances1 whose atoms1 hardly diminished in numbers1 pursue their changes while the mountains come and go1 and the #acc rudiments of life develop into its highest consummations4 ,to those unacquainted with the results of geological investigation the history of the mountains as deciphered in the rocks seems almost incredible4 ,the recently published sections of the ,himalaya1 due to ,h4 ,h4 ,hayden and the many distinguished men who have contributed to the ,geological ,survey of ,india1 show these great ranges to be essentially formed of folded sediments penetrated by vast masses of granite and other eruptives4 ,their geological history may be summarised as follows ,the ,himalayan area in pre-,cambrian times was1 in its southwestern extension1 part of the floor of a sea which covered much of what is now the ,indian ,peninsula4 ,in the northern shallows of this sea were laid down beds of conglomerate1 shale1 sandstone and limestone1 derived from the denudation of ,archan rocks1 which1 probably1 rose as hills or mountains in parts of ,peninsular ,india and along the ,tibetan edge of the ,himalayan region4 ,these beds constitute the record of the long ,purana ,era#a and are probably coeval with the ,algonkian of ,north ,america4 ,even in these early times volcanic disturbances affected this area and the lower beds of the ,purana deposits were penetrated by volcanic outflows1 covered by sheets of lava1 uplifted1 denuded and again submerged #a ,see footnote1 p4 #aci4 #acd beneath the waters4 ,two such periods of instability have left their records in the sediments of the ,purana sea4 ,the succeeding era--the ,dravidian ,era--opens with ,haimanta 7,cambrian7 times4 ,a shallow sea now extended over ,kumaun1 ,garwal1 and ,spiti1 as well as ,kashmir and ultimately over the ,salt ,range region of the ,punjab as is shown by deposits in these areas4 ,this sea was not1 however1 connected with the ,cambrian sea of ,europe4 ,the fossil faunas left by the two seas are distinct4 ,after an interval of disturbance during closing ,haimanta times1 geographical changes attendant on further land movements occurred4 ,the central sea of ,asia1 the ,tethys1 extended westwards and now joined with the ,european ,paleozoic sea2 and deposits of ,ordovician and ,silurian age were laid down3--the ,muth deposits4 ,the succeeding ,devonian ,period saw the whole ,northern ,himalayan area under the waters of the ,tethys which1 eastward1 extended to ,burma and ,china and1 westward1 covered ,kashmir1 the ,hindu ,kush and part of ,afghanistan4 ,deposits continued to be formed in this area till middle ,carboniferous times4 ,near4 the close of the ,dravidian ,era ,kashmir became convulsed by volcanic disturbance and the ,penjal traps were ejected4 ,it was a time of worldwide disturbance and of redistribution of land and water4 ,carboniferous times had begun1 and the geographical changes in #ace the southern limits of the ,tethys are regarded as ushering in a new and last era in ,indian geological history the ,aryan ,bra4 ,india was now part of ,gondwanaland2 that vanished continent which then reached westward to ,south ,africa and eastward to ,australia4 ,a boulder-bed of glacial origin1 the ,talchir ,boulder-bed1 occurs in many surviving parts of this great land4 ,it enters largely into the ,salt ,range deposits4 ,there is evidence that extensive sheets of ice1 wearing down the rocks of ,rajputana1 shoved their moraines northward into the ,salt ,range ,sea2 then1 probably1 a southern extension of the ,tethys4 ,subsequent to this ice age the ,indian coalfields of the ,gondwana were laid down1 with beds rich in the ,glossopteris and ,gangamopteris flora4 ,this remarkable carboniferous flora extends to ,southern ,kashmir1 so that it is to be inferred that this region was also part of the main ,gondwanaland4 ,but its emergence was but for a brief period4 ,upper ,carboniferous marine deposits succeeded2 and1 in fact1 there was no important discontinuity in the deposits in this area from ,panjal times till the early ,tertiaries4 ,during the whole of which vast period ,kashmir was covered with the waters of the ,tethys4 ,the closing ,dravidian disturbances of the ,kashmir region did not1 apparently1 extend to the eastern ,himalayan area4 ,but the ,carboniferous ,period was1 in this #acf eastern area1 one of instability1 culminating1 at the close of the ,period1 in a steady rise of the land and a northward retreat of the ,tethys4 ,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 ,carboniferous1 ,devonian1 and a large part of the ,silurian and ,ordovician deposits were removed--some thousands of feet in thickness--before resubmergence in the ,tethys occurred4 ,towards the end of the ,palaeozoic ,age the ,aryan ,tethys receded westwards1 but still covered the ,himalaya and was still connected with the ,european ,palozoic sea4 ,the ,himalayan area 7as well as ,kashmir7 remained submerged in its waters throughout the entire ,mesozoic ,age4 ,during ,cretaceous times the ,tethys became greatly extended1 indicating a considerable subsidence of northwestern ,india1 ,afghanistan1 ,western ,asia1 and1 probably1 much of ,tibet4 ,the shallow-water character of the deposits of the ,tibetan ,himalaya indicates1 however1 a coast line near this region4 ,volcanic materials1 now poured out1 foreshadow the incoming of the great mountain-building epoch of the ,tertiary ,era4 ,the enormous mass of the ,deccan traps1 possessing a volume which has been estimated at as much as #f1jjj cubic miles1 was probably extruded over the ,northern ,peninsular region during late ,cretaceous times4 ,the sea now began to retreat1 and by the close of #acg the ,eocene1 it had moved westward to ,sind and ,baluchistan4 ,the movements of the ,earth's crust were attended by intense volcanic activity1 and great volumes of granite were injected into the sediments1 followed by dykes and outflows of basic lavas4 ,the ,tethys vanished to return no more4 ,it survives in the ,mediterranean of today4 ,the mountain-building movements continued into ,pliocene times4 ,the ,nummulite beds of the ,eocene were1 as the result1 ultimately uplifted #ah1ejj feet over sea level1 a total uplift of not less than #bj1jjj feet4 ,thus with many vicissitudes1 involving intervals of volcanic activity1 local uplifting1 and extensive local denudation1 the ,himalaya1 which had originated in the sediments of the ancient ,purana sea1 far back in pre-,cambrian times1 and which had developed potentially in a long sequence of deposits collecting almost continuously throughout the whole of geological time1 finally took their place high in the heavens1 where only the winds--faint at such altitudes--and the lights of heaven can visit their eternal snows4#a ,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 surface4 #a ,see ,a ,sketch of the ,geography and ,geology of the ,himalaya ,mountains and ,tibet4 ,by ,colonel ,s4 ,g4 ,burrard1 ,r4,e41 ,f4,r4,s41 and ,h4 ,h4 ,hayden1 ,f4,g4,s41 ,part ,,iv4 ,calcutta1 #aijh4 #ach ,the diagrammatic sections of the ,himalaya accompanying this brief description arc taken from the monograph of ,burrard and ,hayden 7loc4 cit47 on the ,himalaya4 ,looking at the sections we see that some of the loftiest summits are sculptured in granite and other crystalline rocks4 ,the appearance of these materials at the surface indicates the removal by denudation and the extreme metamorphism of much sedimentary deposit4 ,the crystalline rocks1 indeed1 penetrate some of the oldest rocks in the world4 ,they appear in contact with ,archaean1 ,algonkian or early ,palaeozoic rocks4 ,a study of the sections reveals not only the severe earth movements1 but also the immense amount of sedimentary deposits involved in the genesis of these alps4 ,it will be noted that the vertical scale is not exaggerated relatively to the horizontal4#a ,although there is no evidence of mountain building #a ,to those unacquainted with the terminology of ,indian geology the following list of approximate equivalents in time will be of use ,ngari ,khorsum ,beds - ,pleistocene4 ,siwalik ,series - ,miocene and ,pliocene4 ,sirmur ,series - ,oligocene4 ,kampa ,system - ,eocene and ,cretaceous4 ,lilang ,system - ,triassic4 ,kuling ,system - ,permian4 ,gondwana ,system - ,carboniferous4 ,kenawar ,system - ,carboniferous and ,devonian ,muth ,system - ,silurian4 ,haimanta ,system - ,mid4 and ,lower ,cambrian4 ,purana ,group - ,algonkian4 ,vaikrita ,system - ,archan4 ,daling ,series - ,archan4 #aci on a large scale in the ,himalayan area till the ,tertiary upheaval1 it is1 in the majority of cases1 literally correct to speak of the mountains as having their generations like organic beings1 and passing through all the stages of birth1 life1 death and reproduction4 ,the ,alps1 the ,jura1 the ,pyrenees1 the ,andes1 have been remade more than once in the course of geological time1 the dbris of a worn-out range being again uplifted in succeeding ages4 ,thus to dwell for a moment on one case only3 that of the ,pyrenees4 ,the ,pyrenees arose as a range of older ,palmozoic rocks in ,devonian times4 ,these early mountains1 however1 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 rocks4 ,and to ,carboniferous succeeded ,permian1 ,triassic1 ,jurassic and ,lower ,cretaceous sediments all laid down in conformable sequence4 ,there was then fresh disturbance and upheaval followed by denudation1 and these mountains1 in turn1 became worn out and depressed beneath the ocean so that ,upper ,greensand rocks were laid down unconforrnably on all beneath4 ,to these now succeeded ,upper ,chalk1 sediments of ,danian age1 and so on1 till ,eocene times1 when the tale was completed and the existing ranges rose from the sea4 ,today we find the folded ,nummulitic strata of ,eocene age uplifted #aa1jjj feet1 or within #bjj feet of the greatest heights of the ,pyrenees4 ,and so they stand awaiting #adj the time when once again they shall fall into the portion of outworn faces4#a ,only mountains can beget mountains4 ,great accumulations of sediment are a necessary condition for the localisation of crust-flexure4 ,the earliest mountains arose as purely igneous or volcanic elevations1 but the generations of the hills soon originated in the collection of the dbris1 under the law of gravity1 in the hollow places4 ,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 sinking1 another1 from which the sediments were derived1 surely existed4 ,through the windows in the deep-cut rocks of the ,swiss valleys we see the older ,carboniferous ,alps looking out1 revisiting the sun light1 after scores of millions of years of imprisonment4 ,we know that just as surely as the ,alps of today are founding by their muddy torrents ranges yet to arise1 so other primeval ,alps fed into the ocean the materials of these buried pre-,permian rocks4 ,this succession of events only can cease when the rocks have been sufficiently impoverished of the heat-producing substances1 or the forces of compression shall have died out in the surface crust of the earth4 ,it seems impossible to escape the conclusion that in the great development of ocean-encircling areas of #a ,see ,prestwich1 ,chemical and ,physical ,geology1 p4 #cjb4 #ada deposition and crustal folding1 the heat of radioactivity has been a determining factor4 ,we recognise in the movements of the sediments not only an influence localising and accelerating crustal movements1 but one which1 in subservience to the primal distribution of land and water1 has determined some of the greatest geographical features of the globe4 ,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 earth4 ,the association of earthquakes with the great geosynclines is well known4 ,the work of ,de ,montessus showed that over #id per cent4 of all recorded shocks lie in the geosynclinal belts4 ,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 continents4 ,similarly we may view in volcanoes phenomena referable to the same fundamental cause4 ,the volcano was1 in fact1 long regarded as more intimately connected with earthquakes than it1 probably1 actually is2 the association being regarded in a causative light1 whereas the connexion is more that of possessing a common origin4 ,the girdle of volcanoes around the ,pacific and the earthquake belt coincide4 ,again1 the ancient and modern volcanoes and earthquakes of ,europe are associated with the geosyncline of the greater ,mediterranean1 the ,tethys of ,mesozoic times4 ,there is no difficulty in understanding in a #adb general way the nature of the association4 ,the earthquake is the manifestation of rupture and slip1 and1 as ,suess has shown1 the epicentres shift along that fault line where the crust has yielded4#a ,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 surface4 ,in a recent work on the subject of earthquakes ,professor ,hobbs writes3 ,one of the most interesting of the generalisations which ,de ,montessus has reached as a result of his protracted studies1 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 history4 ,within these belts the sedimentary formations of the crust were laid down in the greatest thickness1 and the formations follow each other in relatively complete succession4 ,for almost or quite the whole of this long era it is therefore clear that the ocean covered these zones4 ,about them the formations are found interrupted1 and the lacuna indicate that the sea invaded the area only to recede from it1 and again at some later period to transgress upon it4 ,for a long time1 therefore1 these earthquake belts were the sea basins--the geosynclines4 ,they became later the rising mountains of the ,tertiary period1 and mountains they #a ,suess1 ,the ,face of the ,earth1 vol4 ii41 chap4 ii4 #adc are today4 ,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 crust4#a ,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 areas1 is an obscure and complex question4 ,we seem1 indeed1 according to the views of some authorities1 hardly in a position to affirm with certainty that such widespread movements of the land have actually occurred1 and that the phenomena are not the outcome of fluctuations of oceanic level2 that our observations go no further than the recognition of positive and negative movements of the strand4 ,however this may be1 the greater part of mechanical denudation during geological time has been done on the mountain ranges4 ,it is1 in short1 indisputable that the orogenic movements which uplift the hills have been at the basis of geological history4 ,to them the great accumulations of sediments which now form so large a part of continental land are mainly due4 ,there can be no doubt of the fact that these movements have swayed the entire history1 both inorganic and organic1 of the world in which we live4 #a ,hobbs1 ,earthquakes1 p4 #eh4 #add ,to sum the contents of this essay in the most general terms1 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 significance4 ,the heat of the earth is not internal only1 but rather a heat-source exists at the surface1 which1 as we have seen1 cannot prevail to the same degree within2 and when the conditions become favourable for the aggregation of the energy1 the crust1 heated both from beneath and from above1 assumes properties more akin to those of its earlier stages of development1 the secular heat-loss being restored in the radioactive supplies4 ,these causes of local mobility have been in operation1 shifting somewhat from place to place1 and defined geographically by the continental masses undergoing denudation1 since the earliest times4 #ade ,,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 developing4 ,the ,nummulitic limestones were being laid down in that enlarged ,mediterranean which at this period1 save for a few islands1 covered most of south ,europe4 ,of these stratified remains1 as well as of the great beds of ,cretaceous1 ,jurassic1 ,triassic1 and ,permian sediments beneath1 our hypothetical observer would probably have been regardless2 just as today we observe1 with an indifference born of our transitoriness1 the deposits rapidly gathering wherever river discharge is distributing the sediments over the sea-floor1 or the lime-secreting organisms are actively at work4 ,and yet it took but a few millions of years to uplift the deposits of the ancient ,tethys2 pile high its sediments in fold upon fold in the ,alps1 the ,carpathians1 and the ,himalayas2 and--exposing them to the rigours of denudation at altitudes where glaciation1 landslip1 and torrent prevail--inaugurate a new epoch of sedimentation and upheaval4 #adf ,in the case of the ,alps1 to which we wish now specially to refer1 the chief upheaval appears to have been in ,oligocene times1 although movement continued to the close of the ,pliocene4 ,there was thus a period of some millions of years within which the entire phenomena were comprised4 ,availing ourselves of ,sollas' computations1#a we may sum the maximum depths of sedimentary deposits of the geological periods concerned as follows3-- ,pliocene - - - - - #c1iej m4 ,miocene - - - - - #d1bej m4 ,oligocene - - - - #c1ffj m4 ,eocene - - - - - - #f1ajj m4 and assuming that the orogenic forces began their work in the last quarter of the ,eocene period1 we have a total of #ac1djj m4 as some measure of the time which elapsed4 ,at the rate of io centimetres in a century these deposits could not have collected in less than #ac4d millions of years4 ,it would appear that not less than some ten millions of years were consumed in the genesis of the ,alps before constructive movements finally ceased4 ,the progress of the earth-movements was attended by the usual volcanic phenomena4 ,the ,oligocene and ,miocene volcanoes extended in a band marked by the ,auvergne1 the ,eiffel1 the ,bohemian1 and the eastern ,carpathian eruptions2 and1 later1 towards the close of the movements in ,pliocene times1 the south border #a ,sollas1 ,anniversary ,address1 ,geol4 ,soc41 ,london1 #aiji4 #adg regions of the ,alps became the scene of eruptions such as those of ,etna1 ,santorin1 ,somma 7,vesuvius71 etc4 ,we have referred to these well-known episodes with two objects in view3 to recall to mind the time-interval involved1 and the evidence of intense crustal disturbance1 both dynamic and thermal4 ,according to views explained in a previous essay1 the energetic effects of radium in the sediments and upper crust were a principal factor in localising and bringing about these results4 ,we propose now to inquire if1 also1 in the more intimate structure of the ,alps1 the radioactive energy may not have borne a part4 ,what we see today in the ,alps is but a residue spared by denudation4 ,it is certain that vast thicknesses of material have disappeared4 ,even while constructive effects were still in progress1 denudative forces were not idle4 ,of this fact the shingle accumulations of the ,molasse1 where1 on the northern borders of the ,alps1 they stand piled into mountains1 bear eloquent testimony4 ,in the sub-,apennine series of ,italy1 the great beds of clays1 marls1 and limestones afford evidence of these destructive processes continued into ,pliocene times4 ,we have already referred to ,schmidt's estimate that the sedimentary covering must have in places amounted to from #ae1jjj to #bj1jjj metres4 ,the evidence for this is mainly tectonic or structural2 but is partly forthcoming in the changes which the materials now open to our inspection plainly reveal4 ,thus it is impos- #adh sible to suppose that gneissic rocks can become so far plastic as to flow in and around the calcareous sediments1 or be penetrated by the latter--as we see in the ,jungfrau and elsewhere--unless great pressures and high temperatures prevailed4 ,and1 according to some writers1 the temperatures revealed by the intimate structural changes of rock-forming minerals must have amounted to those of fusion4 ,the existence of such conditions is supported by the observation that where the4crystallisation is now the most perfect1 the phenomena of folding and injection are best developed4#a ,these high temperatures would appear to be unaccountable without the intervention of radiothermal effects2 and1 indeed1 have been regarded as enigmatic by observers of the phenomena in question4 ,a covering of #bj1jjj metres in thickness would not occasion an earth-temperature exceeding #ejj ,c4 if the gradients were such as obtain in mountain regions generally2 and #fjj is about the limit we could ascribe to the purely passive effects of such a layer in elevating the geotherms4 ,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 stated2 for the facts are1 indeed1 very different from the generally preconceived ideas of mountain formation4 ,nor can we wonder that many geologists for long held #a ,weinschenk1 ,c4 ,r4 ,congrs ,gol41 #aijj1 p4 #cba1 et seq4 #adi back from admitting views which appeared so extreme4 ,receptivity is the first virtue of the scientific mind2 but1 with every desire to lay aside prejudice1 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 country1 and the carriage of mountainous materials from the south of the ,alps to the north1 leaving them finally as ,alpine ranges of ancient sediments reposing on foundations of more recent date4 ,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 them4 ,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 founded4 ,the lesser mountains which stand along the northern border of the great limestone ,alps1 those known as the ,pralpes1 present the strange characteristic of resting upon materials younger than themselves4 ,such mountains as the remarkable-looking ,mythen1 near ,schwyz1 for instance1 are weathered from masses of ,triassic and ,jurassic rock1 and repose on the much more recent ,flysch4 ,in sharp contrast to the ,flysch scenery1 they stand as abrupt and gigantic erratics1 which have been transported from the central zone of the ,alps lying far to the south4 ,they are strangers petrologically1 #aej stratigraphically1 and geographically1#a to the locality in which they now occur4 ,the exotic materials may be dolomites1 limestones1 schists1 sandstones1 or rocks of igneous origin4 ,they show in every case traces of the severe dynamic actions to which they have been subjected in transit4 ,the igneous1 like the sedimentary1 klippen1 can be traced to distant sources2 to the massif of ,belladonne1 to ,mont ,blanc1 ,lugano1 and the ,tyrol4 ,the ,pralpes are1 in fact1 mountains without local roots4 ,in this last-named essential feature1 the ,pralpes do not differ from the still greater limestone ,alps which succeed them to the south4 ,these giants1 e4g4 the ,jungfrau1 ,wetterhorn1 ,eiger1 etc41 are also without local foundations4 ,they have been formed from the overthrown and drawn-out anticlines of great crust-folds1 whose synclines or roots are traceable to the south side of the ,rhone ,valley4 ,the ,bernese ,oberland originated in the piling-up of four great sheets or recumbent folds1 one of which is continued into the ,pralpes4 ,with ,lugeon#b we may see in the phenomenon of the formation of the ,pralpes a detail2 regarding it as a normal expression of that mechanism which has created the ,swiss ,alps4 ,for these limestone masses of the ,oberland are not indications of a merely local shift of the sedimentary covering of the ,alps4 ,almost the whole covering has #a ,de ,lapparent1 ,trait de ,gologie1 p4 #a1ghe4 #b ,lugeon1 ,bulletin ,soc4 ,gol4 de ,france1 #aija1 p4 #ggb4 #aea been pushed over and piled up to the north4 ,lugeonl concludes that1 before denudation had done its work and cut off the ,pralpes from their roots1 there would have been found sheets1 to the number of eight1 superimposed and extending between the ,mont ,blanc massif and the massif of the ,finsteraarhorn3 these sheets being the overthrown folds of the wrinkled sedimentary covering4 ,the general nature of the alpine structure ,fig4 #h will be understood from the presentation of it diagrammatically after ,schmidt of ,basel 7,fig4 #h74b ,the section extends from north to south1 and brings out the relations of the several recumbent folds4 ,we must imagine almost the whole of these superimposed folds now removed from the central regions of the ,alps by denudation1 #a ,lugeon1 loc4 cit4 #b ,schmidt1 ,ec4 ,geol4 ,helvetiae1 vol4 ix41 ,no4 #d4 #aeb and leaving the underlying gneisses rising through the remains of ,permian1 ,triassic1 and ,jurassic sediments2 while to the north the great limestone mountains and further north still1 the ,pralpes1 carved from the remains of the recumbent folds1 now stand with almost as little resemblance to the vanished mountains as the memories of the past have to its former intense reality4 ,these views as to the origin of the ,alps1 which are shared at the present day by so many distinguished geologists1 had their origin in the labours of many now gone2 dating back to ,studer2 finding their inspiration in the work of ,heim1 ,suess1 and ,marcel ,bertrand2 and their consummation in that of ,lugeon1 ,schardt1 ,rothpletz1 ,schmidt1 and many others4 ,nor must it be forgotten that nearer home1 somewhat similar phenomena1 necessarily on a smaller scale1 were recognised by ,lapworth1 twenty-six years ago1 in his work on the structure of the ,scottish ,highlands4 ,an important tectonic principle underlies the development of the phenomena we have just been reviewing4 ,the uppermost of the superimposed recumbent folds is more extended in its development than those which lie beneath4 ,passing downwards from the highest of the folds1 they are found to be less and less extended both in the northerly and in the southerly direction1 speaking of the special case--the ,alps--now before us4 ,this feature might be described somewhat differently4 ,we might say that those folds which had their roots farther #aec to the south were the most drawn-out towards the north3 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 fold1 in the advance of the latter to the north4 ,the anticline has advanced relatively to the syncline4 ,to this law one exception only is observed in the ,swiss ,alps2 the sheet of the ,brche 7,byecciendecke7 falls short1 in its northerly extension1 of the underlying fold1 which extends to form the ,pralpes4 ,contemplating such a generalised section as ,professor ,schmidt's1 or1 indeed1 more particular sections1 such as those in the ,mont ,blanc ,massif by ,marcel ,bertrand1#a of the ,dent de ,morcles1 ,diablerets1 ,wildhorn1 and ,massif de la ,brche by ,lugeon1#b or finally ,termier's section of the ,pelvoux ,massif1#c one is reminded of the breaking of waves on a sloping beach4 ,the wave1 retarded at its base1 is carried forward above by its momentum1 and finally spreads far up on the strand2 and if it could there remain1 the succeeding wave must necessarily find itself superimposed upon the first4 ,but no effects of inertia1 no kinetic effects1 may be called to our aid in explaining the formation of mountains4 ,some geologists have accordingly supposed that in order to account for #a ,marcel ,bertrand1 ,cong4 ,gol4 ,internat41 #aijj1 ,guide ,gol41 xiii4 a1 p4 #da4 #b ,lugeon1 loc4 cit41 p4 #ggc4 #c ,de ,lapparent1 ,traite de ,gol41 p4 #a1ggc4 #aed the recumbent folds and the peculiar phenomena of increasing overlap1 or dferlement1 an obstacle1 fixed and deep-seated1 must have arrested the roots or synclines of the folds1 and held them against translational motion1 while a movement of the upper crust drew out and carried forward the anticlines4 ,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 crust4 ,it would appear that the explanation of the phenomena of recumbent folds and their dferlement is to be obtained directly from the temperature conditions prevailing throughout the stressed pile of rocks2 and here the subject of mountain tectonics touches that with which we were elsewhere specially concerned--the geological influence of accumulated radioactive energy4 ,as already shown#a1 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 ,earth1 and the consequent upward movement of the geotherms4 ,the time element is here the most important consideration4 ,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 years4 #a ,mountain ,genesis1 p4 #abi1 et seq4 #aee ,unfortunately the full investigation of the distribution of temperature after any given time is beset with difficulties2 the conditions being extremely complex4 ,if the radioactive heating was strictly adiabatic--that is1 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 years4 ,the conditions are not1 indeed1 adiabatic2 but1 on the other hand1 the rocks upraised by lateral pressure were by no means at #j ,c4 to start with4 ,they must be assumed to have possessed such temperatures as the prior radiothermal effects1 and the conducted heat from the ,earth's interior1 may have established4 ,it would from this appear probable that if a duration of ten million years was involved1 the equilibrium radioactive temperatures must nearly have been attained4 ,the effects of heat conducted from the underlying earthcrust have to be added1 leading to a further rise in temperature of not less than #ejj or #fjj 4 ,in such considerations the observed indications of high temperatures in materials now laid bare by denudation1 probably find their explanation 7,p#a4 ,,xix74 ,the first fact that we infer from the former existence of such a temperature distribution is the improbability1 indeed the impossibility1 that anything resembling a rigid obstacle1 or deep-seated horst1 can have existed beneath the present surface-level1 and opposed the northerly movement of the deep-lying synclines4 ,for #aef 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 ,alps2 and the idea that this could retain rigidity under the prevailing temperature conditions1 must be dismissed4 ,there is no need to labour this question2 the horst cannot have existed4 ,to what1 then1 is the retardation of the lower parts of the folds1 their overthrow1 above1 to the north1 and their dferlement1 to be ascribed8 ,a little consideration shows that the very conditions of high temperature and viscosity1 which render untenable the hypothesis of a rigid obstacle1 suffice to afford a full explanation of the retardation of the roots of the folds4 ,for directed translatory movements cannot be transmitted through a fluid1 pressure in which is necessarily hydrostatic1 and must be exerted equally in every direction4 ,and this applies1 not only to a fluid1 but to a body which will yield viscously to an impressed force4 ,there will be a gradation1 according as viscosity gives place to rigidity1 between the states in which the applied force resolves itself into a purely hydrostatic pressure1 and in which it is transmitted through the material as a directed thrust4 ,the nature of the force1 in the most general case1 of course1 has to be considered2 whether it is suddenly applied and of brief duration1 or steady and long-continued4 ,the latter conditions alone apply to the present case4 ,it follows from this that1 although a tangential force #aeg or pressure be engendered by a crustal movement occurring to the south1 and the resultant effects be transmitted northwards1 these stresses can only mechanically affect the rigid parts of the crust into which they are carried4 ,that is to say1 they may result in folding and crushing1 or horizontally transporting1 the upper layers of the ,earth's crust2 but in the deeper-lying viscous materials they must be resolved into hydrostatic pressure which may act to upheave the overlying covering1 but must refuse to transmit the horizontal translatory movements affecting the rigid materials above4 ,between the regions in which these two opposing conditions prevail there will be no hard and fast line2 but with the downward increase of fluidity there will be a gradual failure of the mechanical conditions and an increase of the hydrostatic4 ,thus while the uppermost layers of the crust may be transported to the full amount of the crustal displacement acting from the south 7speaking still of the ,alps7 deeper down there will be a lesser horizontal movement1 and still deeper there is no influence to urge the viscous rock-materials in a northerly direction4 ,the consequences of these conditions must be the recumbence of the folds formed under the crust-stress1 and their dferlement towards the north4 ,to see this1 we must follow the several stages of development4 ,the earliest movements1 we may suppose1 result in flexures of the ,jura-,mountain type--that is1 in a #aeh succession of undulations more or less symmetrical4 ,as the orogenic force continues and develops1 these undulations give place to folds1 the limbs of which are approximately vertical1 and the synclinal parts of which become ever more and more depressed into the deeper1 and necessarily hotter1 underlying materials2 the anticlines being probably correspondingly elevated4 ,these events are slowly developed1 and the temperature beneath is steadily rising in consequence of the conducted interior heat1 and the steady accumulation of radioactive energy in the sedimentary rocks and in the buried radioactive layer of the ,earth4 ,the work expended on the crushed and sheared rock also contributes to the developing temperature4 ,thus the geotherms must move upwards1 and the viscous conditions extend from below2 continually diminishing the downward range of the translatory movements progressing in the higher parts4 ,while above the folded sediments are being carried northward1 beneath they are becoming anchored in the growing viscosity of the medium4 ,the anticlines will bend over1 and the most southerly of the folds will gradually become pushed or bent over those lying to the north4 ,finally1 the whole upper part of the sheaf will become horizontally recumbent2 and as the uppermost folds will be those experiencing the greatest effects of the continued displacement1 the dferlement or overlap must necessarily arise4 ,we may follow these stages of mountain evolution #aei in a diagram 7,fig4 #i7 in which we eliminate intermediate conditions1 and regard the early and final stages of development only4 ,in the upper sketch we suppose the lateral compression much developed and the upward movement of the geotherms in progress4 ,the dotted line may be assumed to be a geotherm having a temperature of viscosity4 ,if the conditions here shown persist ,fig4 #i indefinitely1 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 north4 ,the second figure is intended to show in what manner these results are evaded4 ,the geotherm of viscosity has risen4 ,all above it is affected mechanically by the continuing stress1 and borne northwards in varying #afj degree depending upon the rigidity4 ,the folds have been overthrown and drawn out2 those which lay originally most to the south have become the uppermost2 and1 experiencing the maximum amount of displacement1 overlap those lying beneath4 ,there has also been a certain amount of upthrow owing to the hydrostatic pressure4 ,this last-mentioned element of the phenomena is of highly indeterminate character1 for we know not the limits to which the hydrostatic pressure may be transmitted1 and where it may most readily find relief4 ,while1 according to some of the published sections1 the uplifting force would seem to have influenced the final results of the orogenic movements1 a discussion of its effects would not be profitable4 #afa ,,other ,,minds ,,than ,,ours8 ,,in the year #afaj ,galileo1 looking through his telescope then newly perfected by his own hands1 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 ,earth4 ,it was a revelation too great to be credited by mankind4 ,it was opposed to the doctrine of the centrality of the ,earth1 for it suggested that other worlds constituted like ours might exist in the heavens4 ,some said it was a mere optic illusion2 others that he who looked through such a tube did it at the peril of his soul--it was but a delusion of ,satan4 ,galileo converted a few of the unbelievers who had the courage to look through his telescope4 ,to the others he said1 he hoped they would see those moons on their way to heaven4 ,old as this story is it has never lost its pathos or its teaching4 ,the spirit which assailed ,galileo's discoveries and which finally was potent to overshadow his declining years1 closed in former days the mouths of those who asked the question written at the head of this lecture3 ,are we to believe that there are other minds than ours8 #afb ,today we consider the question in a very different spirit4 ,few would regard it as either foolish or improper4 ,its intense interest would be admitted by all1 and but for the limitations closing our way on every side it would1 doubtless1 attract the most earnest investigation4 ,even on the mere balance of judgment between the probable and the improbable1 we have little to go on4 ,we know nothing definitely as to the conditions under which life may originate3 whether these are such as to be rare almost to impossibility1 or common almost to certainty4 ,only within narrow limits of temperature and in presence of certain of the elements1 can life like ours exist1 and outside these conditions life1 if such there be1 must be different from ours4 ,once originated it is so constituted as to assail the energies around it and to advance from less to greater4 ,do we know more than these vague facts8 ,yes1 we have in our experience one other fact and one involving much4 ,we know that our world is very old2 that life has been for many millions of years upon it2 and that ,man as a thinking being is but of yesterday4 ,here is then a condition to be fulfilled4 ,to every world is physically assigned a limit to the period during which it is habitable according to our knowledge of life and its necessities4 ,this limit passed and rationality missed1 the chance for that world is gone for ever1 and other minds than ours assuredly will not from it contemplate the universe4 ,looking at our own world we see that the tree of life has1 #afc indeed1 branched1 leaved and1 possibly1 budded many times2 it never bloomed but once4 ,all difficulties dissolve and speculations become needless under one condition only3 that in which rationality may be inferred directly or indirectly by our observations on some sister world in space1 ,this is just the evidence which in recent years has been claimed as derived from a study of the surface of ,mars4 ,to that planet our hope of such evidence is restricted4 ,our survey in all other directions is barred by insurmountable difficulties4 ,unless some meteoric record reached our ,earth1 revelationary of intelligence on a perished world1 our only hope of obtaining such evidence rests on the observation of ,mars' surface features4 ,to this subject we confine our attention in what follows4 ,the observations made during recent years upon the surface features of ,mars have1 excusably enough1 given rise to sensational reports4 ,we must consider under what circumstances these observations have been made4 ,mars comes into particularly favourable conditions for observation every fifteen years4 ,it is true that every two years and two months we overtake him in his orbit and he is then in opposition4 ,that is1 the ,earth is between him and the sun3 he is therefore in the opposite part of the heavens to the sun4 ,now ,mars' orbit is very excentric1 sometimes he is #aci million miles from the sun1 and sometimes he as as much as #aed million miles from the sun4 ,the ,earth's orbit is1 by comparison1 almost #afd a circle4 ,evidently if we pass him when he is nearest to the sun we see him at his best2 not only because he is then nearest to us1 but because he is then also most brightly lit4 ,in such favourable oppositions we are within #ce million miles of him2 if ,mars was in aphelion we would pass him at a distance of #fa million miles4 ,opposition occurs under the most favourable circumstances every fifteen years4 ,there was one in #ahfb1 another in #ahgg1 one in #ahib1 and so on4 ,when ,mars is #ce million miles off and we apply a telescope magnifying #a1jjj diameters1 we see him as if placed #ce1jjj miles off4 ,this would be seven times nearer than we see the moon with the naked eye4 ,as ,mars has a diameter about twice as great as that of the moon1 at such a distance he would look fourteen times the diameter of the moon4 ,granting favourable conditions of atmosphere much should be seen4 ,but these are just the conditions of atmosphere of which most of the ,european observatories cannot boast4 ,it is to the honour of ,schiaparelli1 of ,milan1 that under comparatively unfavourable conditions and with a small instrument1 he so far outstripped his contemporaries in the observation of the features of ,mars that those contemporaries received much of his early discoveries with scepticism4 ,light and dark outlines and patches on the planet's surface had indeed been mapped by others1 and even a couple of the canals sighted2 but at the opposition of #ahgg ,schiaparelli first mapped any considerable #afe number of the celebrated canals and showed that these constituted an extraordinary and characteristic feature of the planet's geography4 ,he called them canali1 meaning thereby channels4 ,it is remarkable indeed that a mistranslation appears really responsible for the initiation of the idea that these features are canals4 ,in #ahhb ,schiaparelli startled the astronomical world by declaring that he saw some of the canals double--that is appearing as two parallel lines4 ,as these lines span the planet's surface for distances of many thousands of miles the announcement naturally gave rise to much surprise and1 as ,i have said1 to much scepticism4 ,but he resolutely stuck to his statement4 ,here is his map of #ahhb4 ,it is sufficiently startling4 ,in #ahib he drew a new map4 ,it adds a little to the former map1 but the doubling was not so well seen4 ,it is just the strangest feature about this doubling that at times it is conspicuous1 at times invisible4 ,a line which is distinctly seen as a single line at one time1 a few weeks later will appear distinctly to consist of two parallel lines2 like railway tracks1 but tracks perhaps #bjj miles apart and up to #c1jjj or even #d1jjj miles in length4 ,many speculations were1 of course1 made to account for the origin of such features4 ,no known surface peculiarity on the ,earth or moon at all resembles these features4 ,the moon's surface as you know is cracked and #aff streaked4 ,but the cracks are what we generally find cracks to be--either aimless1 wandering lines1 or1 if radiating from a centre1 then lines which contract in width as they leave the point of rupture4 ,where will we find cracks accurately parallel to one another sweeping round a planet's face with steady curvature for1 #d1jjj miles1 and crossing each other as if quite unhampered by one another's presence8 ,if the phenomenon on ,mars be due to cracks they imply a uniformity in thickness and strength of crust1 a homogeneity1 quite beyond all anticipation4 ,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 lines4 ,it was also suggested that the surface of the planet was covered with ice and that these were cracks in the ice4 ,this theory has even greater difficulties than the last to contend with4 ,rivers have been suggested4 ,a glance at our own maps at once disposes of this hypothesis4 ,rivers wander just as cracks do and parallel rivers like parallel cracks are unknown4 ,in time the many suggestions were put aside4 ,one only remained4 ,that the lines are actually the work of intelligence2 actually are canals1 artificially made1 constructed for irrigation purposes on a scale of which we can hardly form any conception based on our own earthly engineering structures4 ,during the opposition of #ahid1 ,percival ,lowell1 along with ,a4 ,e4 ,douglass1 and ,w4 ,h4 ,pickering1 #afg observed the planet from the summit of a mountain in ,arizona1 using an #ah-;inch refracting telescope and every resource of delicate measurement and spectroscopy4 ,so superb a climate favoured them that for ten months the planet was kept under continual observation4 ,over #ijj drawings were made and not only were ,schiaparelli's channels confirmed1 but they added #aaf to his #gi1 on that portion of the planet visible at that opposition4 ,they made the further important discovery that the lines do not stop short at the dark regions of the planet's surface1 as hitherto believed1 but go right on in many cases2 the curvature of the lines being unaltered4 ,lowell is an uncompromising advocate of the canal theory4 ,if his arguments are correct we have at once an answer to our question1 ,are there other minds than ours8 ,we must consider a moment ,lowell's arguments2 not that it is my intention to combat them4 ,you must form your own conclusions4 ,i shall lay before you another and1 as ,i venture to think1 more adequate hypothesis in explanation of the channels of ,schiaparelli4 ,we learn1 however1 much from ,lowell's book--it is full of interest4#a ,lowell lays a deep foundation4 ,he begins by showing that ,mars has an atmosphere4 ,this must be granted him till some counter observations are made4 #a ,mars1 by ,percival ,lowell 7,longmans1 ,green ,co471 #ahif1 #afh ,it is generally accepted4 ,what that atmosphere is1 is another matter4 ,he certainly has made out a good case for the presence of water as one of its constituents1 ,it was long known that ,mars possessed white regions at his poles1 just as our ,earth does4 ,the waning of these polar snows--if indeed they are such--with the advance of the ,martian summer1 had often been observed4 ,lowell plots day by day this waning4 ,it is evident from his observations that the snowfall must be light indeed4 ,we see in his map the south pole turned towards us4 ,mars in perihelion always turns his south pole towards the sun and therefore towards the ,earth4 ,we see that between the dates ,june #crd to ,august #crd--or in two months--the polar snow had almost completely vanished4 ,this denotes a very scanty covering4 ,it must be remembered that ,mars even when nearest to the sun receives but half our supply of solar heat and light4 ,but other evidence exists to show that ,mars probably possesses but little water upon his surface4 ,the dark places are not water-covered1 although they have been named as if they were1 indeed1 seas and lakes4 ,various phenomena show this4 ,the canals show it4 ,it would never do to imagine canals crossing the seas4 ,no great rivers are visible4 ,there is a striking absence of clouds4 ,the atmosphere of ,mars seems as serene as that of ,venus appears to be cloudy4 ,mists and clouds1 however1 sometime appear to veil his face and add to the difficulty of #afi making observations near the limb of the planet4 ,lowell concludes it must be a calm and serene atmosphere2 probably only one-seventh of our own in density4 ,the normal height of the barometer in ,mars would then be but four and a half inches4 ,this is a pressure far less than exists on the top of the highest terrestrial mountain4 ,a mountain here must have an altitude of about ten miles to possess so low a pressure on its summit4 ,drops of water big enough to form rain can hardly collect in such a rarefied atmosphere4 ,moisture will fall as dew or frost upon the ground4 ,the days will be hot owing to the unimpeded solar radiation2 the nights bitterly cold owing to the free radiation into space4 ,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 melt4 ,the freer radiation brings about this phenomenon among our own mountains in clear and calm weather4 ,with the progressive melting of the snow upon the pole ,lowell connected many phenomena upon the planet's surface of much interest4 ,the dark spaces appear to grow darker and more greenish4 ,the canals begin to show themselves and reveal their double nature4 ,all this suggests that the moisture liberated by the melting of the polar snow with the advancing year1 is carrying vitality and springtime over the surface of the planet4 ,but how is the water conveyed8 ,lowell believes principally by the canals4 ,these are #agj constructed triangulating the surface of the planet in all directions4 ,what we see1 according to ,lowell1 is not the canal itself1 but the broad band of vegetation which springs up on the arrival of the water4 ,this band is perhaps thirty or forty miles wide1 but perhaps much less1 for ,lowell reports that the better the conditions of observation the finer the lines appeared1 so that they may be as narrow1 possibly1 as fifteen miles4 ,it is to be remarked that a just visible dot on the surface of ,mars must possess a diameter of #cj miles4 ,but a chain of much smaller dots will be visible1 just as we can see such fine objects as spiders' webs4 ,the widening of the canals is then accounted for1 according to ,lowell1 by the growth of a band of vegetation1 similar to that which springs into existence when the floods of the ,nile irrigate the plains of ,egypt4 ,if no other explanation of the lines is forthcoming than that they are the work of intelligence1 all this must be remembered4 ,if all other theories fail us1 much must be granted ,lowell4 ,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 mercury4 ,zurbriggen has recently got to the top of ,aconcagua1 a height of #bd1jjj feet4 ,on the summit of such a mountain the barometer must stand at about ten inches4 ,why should not beings be developed by evolution with a lung capacity capable of living at two and a half times this altitude4 ,those steadily #aga curved parallel lines are1 indeed1 very unlike anything we have experience of4 ,it would be rather to be expected that another civilisation than our own would present many wide differences in its development4 ,what then is the picture we have before us according to ,lowell8 ,it is a sufficiently dramatic one4 ,mars is a world whose water supply1 never probably very abundant1 has through countless years been drying up1 sinking into his surface4 ,but the inhabitants are making a brave fight for it1 ,they have constructed canals right round their world so that the water1 which otherwise would run to waste over the vast deserts1 is led from oasis to oasis4 ,here the great centres of civilisation are placed3 their ,londons1 ,viennas1 ,new ,yorks4 ,these gigantic works are the works of despair4 ,a great and civilised world finds death staring it in the face4 ,they have had to triple their canals so that when the central canal has done its work the water is turned into the side canals1 in order to utilise it as far as possible4 ,through their splendid telescopes they must view our seas and ample rivers2 and must die like travellers in the desert seeing in a mirage the cool waters of a distant lake4 ,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 civilisation4 ,they would leave some memory of it3 they would have us witness how great was that civilisation before they perish6 ,i close this dramatic picture with the poor comfort #agb that several philanthropic people have suggested signalling to them as a mark of sympathy4 ,it is said that a fortune was bequeathed to the ,french ,academy for the purpose of communicating with the ,martians4 ,it has been suggested that we could flash signals to them by means of gigantic mirrors reflecting the light of our ,sun4 ,or1 again1 that we might light bonfires on a sufficiently large scale4 ,they would have to be about ten miles in diameter6 ,a writer in the ,pall ,mall ,gazette suggested that there need really be no difficulty in the matter4 ,with the kind cooperation of the ,london ,gas ,companies 7this was before the days of electric lighting7 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 ,london1 a signal which would be visible to the astronomers in ,mars would result4 ,he adds1 naively3 ,if only tried for an hour each night some results might be obtained4 ,,ii ,we have reviewed the theory of the artificial construction of the ,martian lines4 ,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 grounds4 ,if it is apparent that such #agc lines would be formed with great probability under certain conditions1 which conditions are themselves probable1 then the argument by exclusion for the existence of civilisation on ,mars1 at once breaks down4 ,fig4 #aj ,as a romance writer is sometimes under the necessity of transporting his readers to other scenes1 so ,i must now ask you to consent to be transported some millions #agd of miles into the region of the heavens which lies outside ,mars' orbit4 ,between ,mars and ,jupiter is a chasm of #cda millions of miles4 ,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 ,sun4 ,a society was formed at the close of the last century for the detection of the missing world4 ,on the first day of the last century1 ,piazzi--who1 by the way1 was not a member of the society--discovered a tiny world in the vacant gap4 ,although eagerly welcomed1 as better than nothing1 it was a disappointing find4 ,the new world was a mere rock4 ,a speck of about #afj miles in diameter4 ,it was obviously never intended that such a body should have all this space to itself4 ,and1 sure enough1 shortly after1 another small world was discovered4 ,then another was found1 and another1 and so on2 and now more than #djj of these strange little worlds are known4 ,but whence came such bodies8 ,the generally accepted belief is that these really represent a misbegotten world4 ,when the ,sun was younger he shed off the several worlds of our system as so many rings4 ,each ring then coalesced into a world4 ,neptune being the first born2 ,mercury the youngest born4 ,after ,jupiter was thrown off1 and the ,sun had shrunk away inwards some #bjo million miles1 he shed off another ring4 ,meaning that this offspring of his should grow up like the rest1 develop into a stable world with the #age potentiality even1 it may be1 of becoming the abode of rational beings4 ,but something went wrong4 ,it broke up into a ring of little bodies1 circulating around him4 ,it is probable on this hypothesis that the number we are acquainted with does not nearly represent the actual number of past and present asteroids4 ,it would take #abe1jjj of the biggest of them to make up a globe as big as our world4 ,they1 so far as they are known1 vary in size from #aj miles to #afj miles in diameter4 ,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 numbered1 and possibly number1 many hundreds of thousands4 ,some of these little bodies are very peculiar in respect to the orbits they move in4 ,this peculiarity is sometimes in the eccentricity of their orbits1 sometimes in the manner in which their orbits are tilted to the general plane of the ecliptic1 in which all the other planets move4 ,the eccentricity1 according to ,proctor1 in some cases may attain such extremes as to bring the little world inside ,mars' mean distance from the sun4 ,this1 as you will remember1 is very much less than his greatest distance from the sun4 ,the entire belt of asteroids--as known--lie much nearer to ,mars than to ,jupiter4 ,as regards the tilt of their orbits1 some are actually as much as #cd degrees inclined to the ecliptic1 so that in fact they are seen from the ,earth among our polar constellations4 #agf ,from all this you see that ,mars occupies a rather hot comer in the solar system4 ,is it not possible that more than once in the remote past ,mars may have encountered one of these wanderers8 ,if he came within a certain distance of the small body his great mass would sway it from its orbit1 and under certain conditions he would pick up a satellite in this manner4 ,that his present satellites were actually so acquired is the suggestion of ,newton1 of ,yale ,college4 ,mars' satellites are indeed suspiciously and most abnormally small4 ,i have not time to prove this to you by comparison with the other worlds of the solar system4 ,in fact1 they were not discovered till #ahgg--;although they were predicted in a most curious manner1 with the most uncannily accurate details1 by ,swift4 ,one of these bodies is about #cf miles in diameter4 ,this is ,phobos4 ,phobos is only #c4gjj miles from the surface of ,mars4 ,the other is smaller and further off4 ,he is named ,deimos1 and his diameter is only #aj miles4 ,he is #ab1ejj miles from ,mars' surface4 ,with the exception of ,phobos the next smallest satellite known in the solar system is one of ,saturn's--,hyperion2 almost #hjj miles in diameter4 ,the inner one goes all round ,mars in #g hours4 ,this is ,phobos' month4 ,mars turns on his axis in #bd hours and #dj minutes1 so that people in ,mars would see the rise of ,phobos twice in the course of a day and night2 lie would apparently cross the sky #agg going against the other satellite2 that is1 he would move apparently from west to east4 ,we may at least assume as probable that other satellites have been gathered by ,mars in the past from the army of asteroids4 ,some of the satellites so picked up would be direct3 that is1 would move round the planet in the direction of his axial rotation4 ,others1 on the chances1 would be retrograde3 that is1 would move against his axial rotation4 ,they would describe orbits making the same various angles with the ecliptic as do the asteroids2 and we may be sure they would be of the same varying dimensions4 ,we go on to inquire what would be the consequence to ,mars of such captures4 ,a satellite captured in this manner is very likely to be pulled into the ,planet4 ,this is a probable end of a satellite in any case4 ,it will probably be the end of our satellite too4 ,the satellite ,phobos is indeed believed to be about to take this very plunge into his planet4 ,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 planet1 it is pretty certain that its career as a satellite will be a brief one4 ,the reasons for this ,i cannot now give4 ,if1 then1 ,mars picked up satellites he is very sure to have absorbed them sooner or later4 ,sooner if they happened to be retrograde satellites1 later if direct satellites4 ,his present satellites are recent additions4 ,they are direct4 #agh ,the path of an expiring satellite will be a slow spiral described round the planet4 ,the spiral will at last1 after many years1 bring the satellite down upon the surface of the primary4 ,its final approach will be accelerated if the planet possesses an atmosphere1 as ,mars probably does4 ,a satellite of the dimensions of ,phobos--that is #cf miles in diameter--would hardly survive more than #cj to #fj years within seventy miles of ,mars' surface4 ,it will then be rotating round ,mars in an hour and forty minutes1 moving1 in fact1 at the rate of #b4b miles per second4 ,in the course of this #cj or #fj years it will1 therefore1 get round perhaps #bjj1jjj times1 before it finally crashes down upon the ,martians4 ,during this closing history of the satellite there is reason to believe1 however1 that it would by no means pursue continually the same path over the surface of the planet4 ,there are many disturbing factors to be considered4 ,being so small any large surface features of ,mars would probably act to perturb the orbit of the satellite4 ,the explanation of ,mars' lines which ,i suggest1 is that they were formed by the approach of such satellites in former times4 ,i do not mean that they are lines cut into his surface by the actual infall of a satellite4 ,the final end of the satellite would be too rapid for this1 ,i think4 ,but ,i hope to be able to show you that there is reason to believe that the mere passage of the satellite1 say at #gj miles above the surface of the planet1 will1 in itself1 give rise to effects on the crust of the planet capable #agi of accounting for just such single or parallel lines as we see4 ,in the first place we have to consider the stability of the satellite4 ,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 half1 and that the centrifugal force is less on the inner than on the outer hemisphere4 ,hence there exists a force tending to tear the satellite asunder on the equatorial section tangential ,fig4 #aa to the planet's surface4 ,if in a fluid or plastic state1 ,phobos1 for instance1 could not possibly exist near the planet's surface4 ,the forces referred to would decide its fate4 ,it may be shown by calculation1 however1 that if ,phobos has the strength of basalt or glass there would remain a considerable coefficient of safety in favour of the satellite's stability2 even when the surfaces of planet and satellite were separated by only five miles4 ,we have now to consider some things which we expect will happen before the satellite takes its final plunge into the planet4 #ahj ,this diagram 7,fig4 #aa7 shows you the satellite travelling above the surface of the planet4 ,the satellite is advancing towards1 or away from1 the spectator4 ,the planet is supposed to show its solid crust in cross section1 which may be a few miles in thickness4 ,below this is such a hot plastic magma as we have reason to believe underlies much of the solid crust of our own ,earth4 ,now there is an attraction between the satellite and the crust of the planet2 the same gravitational attraction which exists between every particle of matter in the universe4 ,let us consider how this attraction will affect the planet's crust4 ,i have drawn little arrows to show how we may consider the attraction of the satellite pulling the crust of the planet not only upwards1 but also pulling it inwards beneath the satellite4 ,i have made these arrows longer where calculation shows the stress is greater4 ,you see that the greatest lifting stress is just beneath the satellite1 whereas the greatest stress pulling the crust in under the satellite is at a point which lies out from under the satellite1 at a considerable distance4 ,at each side of the satellite there is a point where the stress pulling on the crust is the greatest4 ,of the two stresses the lifting stress will tend to raise the crust a little2 the pulling stress may in certain cases actually tear the crust across2 as at ,a and ,b4 ,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 greatest4 ,we must assume the satellite to be a certain size and density2 we must also assume the crust of #aha ,mars to be of some certain density4 ,to fix our ideas on these points ,i take the case of the present satellite ,phobos4 ,what amount of stress will he exert upon the crust of ,mars when he approaches within1 say1 #dj miles of the planet's surface8 ,we know his size approximately--he is about #cf miles in diameter4 ,we can guess his density to be between four times that of water and eight times that of water4 ,we may assume the density of ,mars' surface to be about the same as that of our ,earth's surface1 that is three times as dense as water4 ,we now find that the greatest stress tending to rend open the surface crust of ,mars will be between #d1jjj and #h1jjj pounds to the square foot according to the density we assign to ,phobos4 ,will such a stress actually tear open the crust8 ,we are not able to answer this question with any certainty4 ,much will depend upon the nature and condition of the crust4 ,thus1 suppose that we are here 7,fig4 #ab7 looking down upon the satellite which is moving along slowly relatively to ,mars' surface1 in the direction of the arrow4 ,the satellite has just passed over a weak and cracked part of the planet's crust4 ,here the stress has been sufficient to start two cracks4 ,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 beginning4 ,here the stress from the satellite has got to the edge of the crust4 ,it is greatly concentrated just at the extremities of the cracks4 ,it will1 unler such circumstances probably carry on the #ahb tear4 ,if it does not do so this time1 remember the satellite will some hours later be coming over the same place again1 and then again for1 at least1 many hundreds of times4 ,then also we are not limited to the assumption that the ,fig4 #ab satellite is as small as ,phobos4 ,suppose we consider the case of a satellite approaching ,mars which has a diameter double that of ,phobos2 a diameter still much less than that of the larger class of asteroids4 ,even at the distance #ahc of #fe miles the stress will now amount to as much as from #ae to #cj tons per square foot4 ,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 vent4 ,that is1 we might expect along these lines all the phenomena of upheaval and volcanic eruption which give rise to surface elevations4 ,the probable effect of a satellite of this dimension travelling slowly relatively to the surface of ,mars is1 then1 to leave a very conspicuous memorial of his presence behind him4 ,you see from the diagram that this memorial will consist o3 two parallel lines of disturbance4 ,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 planet4 ,if the satellite stood still above the surface the gravitational stress in the crust would1 of course1 be exerted radially outwards from the centre of the satellite4 ,it would attain at the central point beneath the satellite its maximum vertical effect1 and at some radial distance measured outwards from this point1 which distance we can calculate1 its maximum horizontal tearing effect4 ,when the satellite moves relatively to the planet's crust1 the horizontal tearing force acts differently according to whether it is directed in the line of motion or at right angles to this line4 ,in the direction of motion we see that the satellite #ahd creates as it passes over the crust a wave of rarefaction or tension as at ,d1 followed by compression just beneath the satellite and by a reversed direction of gravitational pull as the satellite passes onwards4 ,these stresses rapidly replace one another as the satellite travels along4 ,they are resisted by the inertia of the crust1 and are taken up by its elasticity4 ,the nature of this succession of alternate compressions and rarefactions in the crust possess some resemblance to those arising in an earthquake shock4 ,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 crust4 ,at each passage of the satellite the horizontal tearing stress increases to a maximum1 when it is exerted laterally1 along the line passing through the horizontal projection of the satellite and at right angles to the line of motion1 and again dies away4 ,it is always a tearing stress1 renewed again and again4 ,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 satellite4 ,the distance separating these lines depend upon the elevation of the satellite above the planet's surface4 ,such lines mark out the theoretical axes of the double canals which future crustal movements will more fully develop4 ,it is interesting to consider what the effect of such #ahe conditions would be if they arose at the surface of our own planet4 ,we assume a horizontal force in the crust adequate to set up tensile stresses of the order1 say1 of fifteen tons to the square foot and these stresses to be repeated every few hours2 our world being also subject to the dynamic effects we recognise in and beneath its crust4 ,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 movements4 ,the relief of stresses1 from whatever cause arising1 in and beneath the crust must surely take place in these regions of disturbance and along these linear areas4 ,here must become concentrated the folding movements1 which are under existing conditions brought into the geosynclines1 along with their attendant volcanic phenomena4 ,in the case of ,mars such a concentration of tectonic events would not1 owing to the absence of extensive subaerial denudation and great oceans1 be complicated by the existence of such synclinal accumulations as have controlled terrestrial surface development4 ,with the passage of time the linear features would probably develop2 the energetic substratum continually asserting its influence along such lines of weakness4 ,it is in the highest degree probable that radioactivity plays no less a part in ,martian history than in terrestrial4 ,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 history4 #ahf ,how far willl these effects resemble the double canals of ,mars8 ,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 #bbj miles apart4 ,what the distance between the lines will be1 as already stated1 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 it4 ,if the satellite does its work at a point lower down above the surface the canal produced will be narrower4 ,the stresses1 too1 will then be much greater4 ,i must also observe that once the crust has yielded to the pulling stress1 there is great probability that in future revolutions of the satellite a central fracture will result4 ,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 satellite4 ,it is thus quite possible that the passage of a satellite may give rise to triple lines4 ,there is reason to believe that the canals on ,mars are in some cases triple4 ,i have spoken all along of the satellite moving slowly over the surface of ,mars4 ,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 great4 ,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 #ahg as three miles a second or even rather more4 ,the stresses set up are1 in such cases1 very difficult to estimate4 ,it has not yet been done4 ,parallel lines of greatest stress or impulse ought to be formed as in the other case4 ,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 ,mars4 ,i may put the fresh evidence to which ,i refer1 in this way3 ,in ,lowell's map 7,p#a4 ,,xxii1 p4 #aib71 and in a less degree in ,schiaparelli's map 7ante p4 #aff71 we are given the course of the lines as fragments of incomplete curves4 ,now these curves might have been anything at all4 ,we must take them as they are1 however1 when we apply them as a test of the theory that the motion of a satellite round ,mars can strike such lines4 ,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 hypothesis4 ,we must begin by realising what sort of curves a satellite which disturbs the surface of a planet would leave behind it after its demise4 ,you might think that the satellite revolving round and round the planet must simply describe a circle upon the spherical surface of the planet3 a great circle as it is called2 that is the greatest circle which can be described upon a sphere4 ,this great circle can1 however1 only be struck1 as you will see1 when the planet is not turning upon its axis3 a condition not likely to be realised4 ,this diagram 7,,pi4 ,,xxi7 shows the surface of a globe #ahh covered with the usual imaginary lines of latitude and longitude4 ,the orbit of a supposed satellite is shown by a line crossing the sphere at some assumed angle with the equator4 ,along this line the satellite always moves at uniform velocity1 passing across and round the back of the sphere and again across4 ,if the sphere is not turning on its polar axis then this satellite1 which we will suppose armed with a pencil which draws a line upon the sphere1 will strike a great circle right round the sphere4 ,but the sphere is rotating4 ,and it is to be expected that at different times in a planet's history the rate of rotation varies very much indeed4 ,there is reason to believe that our own day was once only #b hours long1 or thereabouts4 ,after a preliminary rise in velocity of axial rotation1 due to shrinkage attending rapid cooling1 a planet as it advances in years rotates slower and slower4 ,this phenomenon is due to tidal influences of the sun or of satellites4 ,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 on4 ,the effect of the rotation of the planet will be1 of course1 that as the satellite advances with its pencil it finds the surface of the sphere being displaced from under it4 ,the line struck ceases to be the great circle but wanders off in another curve--which is in fact not a circle at all4 ,you will readily see how we find this curve4 ,suppose the sphere to be rotating at such a speed that while the satellite is advancing the distance ,oa1 the point b on the #ahi sphere will be carried into the path of the satellite4 ,the pencil will mark this point4 ,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 pencil4 ,this curve is then the track marked out by the revolving satellite4 ,you see it dotted round the back of the sphere to where it cuts the equator at a certain point4 ,the course of the curve and the point where it cuts the equator1 before proceeding on its way1 entirely depend upon the rate at which we suppose the sphere to be rotating and the satellite to be describing the orbit4 ,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 equator1 the span of the curve4 ,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 planet4 ,but the nature of events might have been somewhat different4 ,the satellite is1 in the figure1 supposed to be rotating round the sphere in the same direction as that in which the sphere is turning4 ,it might have been that ,mars had picked up a satellite travelling in the opposite direction to that in which he was turning4 ,with the velocity of planet on its axis and of satellite in its orbit the same as before1 a different curve would have been described4 ,the span of the curve due to a retrograde satellite will be greater than that due to a direct satellite4 ,the retrograde satellite will have a span more than half #aij way round the planet1 the direct satellite will describe a curve which will be less than half way round the planet3 that is a span due to a retrograde satellite will be more than #ahj degrees1 while the span due to a direct satellite will be less than #ahj degrees upon the planet's equator4 ,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 equator4 ,this only decides how far the curve marked out by the satellite will recede from the equator4 ,we find then1 so far1 that it is easy to distinguish between the direct and the retrograde curves4 ,the span of one is less1 of the other greater1 than #ahj degrees4 ,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 planet4 ,but of these two velocities that of the satellite may be taken as sensibly invariable1 when close enough to use his pencil4 ,this depends upon the law of centrifugal force1 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 centre4 ,the other velocity--that of the planet upon its axis--was1 as we have seen1 not in the past what it is now4 ,if then ,mars1 at various times in his past history1 picked up satellites1 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 only4 #aia ,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 ,mars8 ,to do this we must apply to ,lowell's map4 ,we pick out preferably1 of course1 the most complete and definite curves4 ,the chain of canals of which ,acheron and ,erebus are members mark out a fairly definite curve4 ,we produce it by eye1 preserving the curvature as far as possible1 till it cuts the equator4 ,reading the span on the equator we find' it to be #bee degrees4 ,in the first place we say then that this curve is due to a retrograde satellite4 ,we also note on ,lowell's map that the greatest rise of the curve is to a point about #cb degrees north of the equator4 ,this gives the inclination of the satellite's orbit to the plane of ,mars' equator4 ,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 satellite4 ,the final question now remains ,if we determine the curve due to this velocity of ,mars on its axis1 will this curve fit that one which appears on ,lowell's map1 and of which we have really availed ourselves of only three points8 ,to answer this question we plot upon a sphere1 the curve of a satellite1 in the manner ,i have described1 assigning to this sphere the velocity derived from the span of #bee degrees4 ,having plotted the curve on the sphere it only remains to transfer it to ,lowell's map4 ,this is easily done4 #aib ,this map 7,pl4 ,,xxii7 shows you the result of treating this1 as well as other curves1 in the manner just described4 ,you see that whether the fragmentary curves are steep and receding far from the equator2 or whether they are flat and lying close along the equator2 whether they span less or more than #ahj degrees2 the curves determined on the supposition that they are the work of satellites revolving round ,mars agree with the mapped curves2 following them with wonderful accuracy2 possessing their properties1 and1 indeed1 in some cases1 actually coinciding with them4 ,i may add that the inadmissible span of #ahj degrees and spans very near this value1 which are not well admissible1 are so far as ,i can find1 absent4 ,the curves are not great circles4 ,you will require of me that ,i should explain the centres of radiation so conspicuous here and there on ,lowell's map4 ,the meeting of more than two lines at the oases is a phenomenon possibly of the same nature and also requiring explanation4 ,in the first place the curves to which ,i have but briefly referred actually give rise in most cases to nodal1 or crossing points2 sometimes on the equator1 sometimes off the equator2 through which the path of the satellite returns again and again4 ,these nodal points will not1 however1 afford a general explanation of the many-branched radiants4 ,it is probable that we should refer such an appearance #aic as is shown at the ,sinus ,titanum to the perturbations of the satellite's path due to the surface features on ,mars4 ,observe that the principal radiants are situated upon the boundary of the dark regions or at the oases4 ,higher surface levels may be involved in both cases4 ,some marked difference in topography must characterise both these features4 ,the latter may possibly originate in the destruction of satellites4 ,or again1 they may arise in crustal disturbance of a volcanic nature1 primarily induced or localised by the crossing of two canals4 ,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 lines4 ,we must here recall what observers say of the multiplicity of the canals4 ,according to ,lowell1 ,what their number maybe lies quite beyond the possibility of count at present2 for the better our own air1 the more of them are visible4 ,such innumerable canals are just what the present theory requires4 ,an in-falling satellite will1 in the course of the last #fj or #hj years of its career1 circulate some #ajj1jjj times over ,mars' surface4 ,now what will determine the more conspicuous development of a particular canal8 ,the mass of the satellite2 the state of the surface crust2 the proximity of the satellite2 and the amount of repetition over the same ground4 ,the after effects may be taken as proportional to the primary disturbance4 #aid ,it is probable that elevated surface features will influence two of these conditions3 the number of repetitions and the proximity to the surface4 ,a tract #ajj miles in diameter and elevated #e1jjj or #aj1jjj feet would seriously perturb the orbit of such a body as ,phobos4 ,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 surface4 ,it is even to be considered if such a mass might not become nodal to the satellite's orbit1 so that this passed through or above this point at various inclinations with its primary direction4 ,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 surface4 ,the lines most conspicuous in the telescope are1 in short1 those which have been favoured by a combination of circumstances as reviewed above1 among which crustal features have1 in some cases1 played a part4 ,i must briefly refer to what is one of the most interesting features of the ,martian lines3 the manner in which they appear to come and go like visions4 ,something going on in ,mars determines the phenomenon4 ,on a particular night a certain line looks single4 ,a few nights later signs of doubling are perceived1 and later still1 when the seeing is particularly good1 not one but two lines are seen4 ,thus1 as an example1 we may take the case of ,phison and ,euphrates4 ,faint glimpses of the dual state were detected in the summer #aie and autumn1 but not till ,november did they appear as distinctly double4 ,observe that by this time the ,antarctic snows had melted1 and there was in addition1 sufficient time for the moisture so liberated to become diffused in the planet's atmosphere4 ,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 atmosphere1 by the fact that the definition appeared progressively better from the south pole upwards as the snow disappeared4 ,lowell thinks this points to vegetation springing up under the influence of moisture2 he considers1 however1 as we have seen1 that the canals convey the moisture4 ,he has to assume the construction of triple canals to explain the doubling of the lines4 ,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 vanishes4 ,we need not necessarily even suppose vegetation concerned4 ,with respect to this last possibility we may remark that the colour observations1 upon which the idea of vegetation is based1 are likely to be uncertain owing to possible fatigue effects where a dark object is seen against a reddish background4 ,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 ranges1 #aif ,we assume a serene and rare atmosphere3 the nights intensely cold1 the days hot with the unveiled solar radiation4 ,on the hill tops the cold of night will be still more intense and so1 also1 will the solar radiation by day4 ,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 melt2 and1 just as we see a heavy dew-fall darken the ground in summer1 so the melting ice will set off the elevated land against the arid plains below4 ,our valleys are more moist than our mountains only because our moisture is so abundant that it drains off the mountains into the valleys4 ,if moisture was scarce it would distil from the plains to the colder elevations of the hills4 ,on this view the accentuation of a canal is the result of meteorological effects such as would arise in the ,martian climate2 effects which must be influenced by conditions of mountain elevation1 atmospheric currents1 etc4 ,we1 thus1 follow ,lowell in ascribing the accentuation of the canals to the circulation of water in ,mars2 but we assume a simple and natural mode of conveyance and do not postulate artificial structures of all but impossible magnitude4 ,that vegetation may take part in the darkening of the elevated tracts is not improbable4 ,indeed we would expect that in the ,martian climate these tracts would be the only fertile parts of the surface4 ,clouds also there certainly are4 ,more recent observations #aig appear to have set this beyond doubt4 ,their presence obviously brings in other possible explanations of the coming and going of elevated surface features4 ,finally1 we may ask what about the reliability of the maps8 ,about this it is to be said that the most recent map--that by ,lowell--has been confirmed by numerous drawings by different observers1 and that it is1itself the result of over #ijj drawings4 ,it has become a standard chart of ,mars1 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 on1 as1 also1 the general features of the planet's surface4 ,the question of the possibility of illusion has frequently been raised4 ,what ,i have said above to a great extent answers such objections4 ,the close agreement between the drawings of different observers ought really to set the matter at rest4 ,recently1 however1 photography has left no further room for scepticism4 ,first photographed in #aije1 the planet has since been photographed many thousands of times from various observatories4 ,a majority of the canals have been so mapped4 ,the doubling of the canals is stated to have been also so recorded4#a ,the hypothesis which ,i have ventured to put before you involves no organic intervention to account for the #a ,e4 ,c4 ,slipher's paper in ,popular ,astronomy for ,march1 #aiad1 gives a good account of the recent work4 #aih details on ,mars' surface4 ,they are physical surface features4 ,mars presents his history written upon his face in the scars of former encounters--like the shield of ,sir ,launcelot4 ,some of the most interesting inferences of mathematical and physical astronomy find a confirmation in his history4 ,the slowing down in the rate of axial rotation of the primary2 the final inevitable destruction of the satellite2 the existence in the past of a far larger number of asteroids than we at present are acquainted with2 all these great facts are involved in the theory now advanced4 ,if justifiably1 then is ,mars' face a veritable ,principia4 ,to fully answer the question which heads these lectures1 we should go out into the populous solitudes 7if the term be permitted7 which lie beyond our system4 ,it is well that there is now no time left to do so2 for1 in fact1 there we can only dream dreams wherein the limits of the possible and the impossible become lost4 ,the marvel of the infinite number of stars is not so marvellous as the rationality that fain would comprehend them4 ,in seeking other minds than ours we seek for what is almost infinitely complex and coordinated in a material universe relatively simple and heterogeneous4 ,in our mental attitude towards the great question1 this fact must be regarded as fundamental4 ,i can only fitly close a discourse which has throughout weighed the question of the living thought against the unthinking laws of matter1 by a paraphrase of the words #aii of a great poet when he1 in higher and1 perhaps1 more philosophic language1 also sought to place the one in comparison with the other4#a ,richter thought that he was--with his human heart unstrengthened--taken by an angel among the universe of stars4 ,then1 as they journeyed1 our solar system was sunken like a faint star in the abyss1 and they travelled yet further1 on the wings of thought1 through mightier systems3 through all the countless numbers of our galaxy4 ,but at length these also were left behind1 and faded like a mist into the past4 ,but this was not all4 ,the dawn of other galaxies appeared in the void4 ,stars more countless still with insufferable light emerged4 ,and these also were passed4 ,and so they went through galaxies without number till at length they stood in the great ,cathedral of the ,universe4 ,endless were the starry aisles2 endless the starry columns2 infinite the arches and the architraves of stars4 ,and the poet saw the mighty galaxies as steps descending to infinity1 and as steps going up to infinity4 ,then his human heart fainted and he longed for some narrow cell2 longed to lie down in the grave that he might hide from infinity4 ,and he said to the angel3 ,angel1 ,i can go with thee no farther4 ,is there1 then1 no end to the universe of stars8 #a ,de ,quincy in his ,system of the ,heavens gives a fine paraphrase of ,richter's ,dream4 #bjj ,then the angel flung up his glorious hands to the heaven of heavens1 saying ,end is there none to the universe of ,god8 ,lo6 also there is no beginning4 #bja ,,the ,,latent ,,image #a ,my inclination has led me1 in spite of a lively dread of incurring a charge of presumption1 to address you principally on that profound and most subtle question1 the nature and mode of formation of the photographic image4 ,i am impelled to do so1 not only because the subject is full of fascination and hopefulness1 but because the wide topics of photographic methods or photographic applications would be quite unfittingly handled by the president you have chosen4 ,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 which1 as ,i submit1 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 nature4 ,but few1 if any1 instances of chemical combination or decomposition are known at so low a temperature4 ,purely chemical actions cease1 indeed1 at far higher temperatures1 fluorine being among the few bodies which still show #a ,presidential address to the ,photographic ,convention of the ,united ,kingdom1 ,july1 #aije4 ,nature1 ,vol4 #gb1 p4 #cjh4 #bjb chemical activity at the comparatively elevated temperature of -#ahj ,c4 ,in short1 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 which1 as in the case of radioactivity or fluorescence1 is not restricted to intervals of temperature over which active molecular vis viva prevails4 ,it compels us to regard with doubt the role of oxidation or other chemical action as essential1 but rather points to the view that such effects must be secondary or subsidiary4 ,we feel1 in a word1 that we must turn for guidance to some purely photo-physical effect4 ,here1 in the first place1 we naturally recall the views of ,bose4 ,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 wave1 converting it into what might be regarded as an allotropic modification of the normal bromide which subsequently responds specially to the attack of the developer4 ,the function of the sensitiser1 according to this view1 is to retard the recovery from strain4 ,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 light4 ,this theory1 whatever it may have to recommend it1 can hardly be regarded as offering a fundamental explanation4 ,in the first place1 we are left in the dark as to what #bjc the strain may be4 ,it may mean many and various things4 ,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 activity4 ,finally1 as will be seen later1 it is hardly adequate to account for the varying degrees of stability which may apparently characterise the latent image4 ,still1 there is much in ,bose's work deserving of careful consideration4 ,he has by no means exhausted the line of investigation he has originated4 ,another theory has doubtless been in the minds of many4 ,i have said we must seek guidance in some photo-physical phenomenon4 ,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 atom4 ,i refer to the phenomena of photo-electricity4 ,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 substances4 ,for long no explanation of the cause of this appeared4 ,but the electron--the ubiquitous electron--is now known with considerable certainty to be responsible4 ,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 body4 ,each electron carries away a very small charge of negative electrification4 ,if1 then1 a body is #bjd originally charged negatively1 it will be gradually discharged by this convective process4 ,if it is not charged to start with1 the electrons will still be liberated at the surface of the body1 and this will acquire a positive charge4 ,if the body is positively charged at first1 we cannot discharge it by illumination4 ,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 detected4 ,suffice it to say1 in further connection with the ,hertz effect1 that when projected among gaseous molecules the electron soon attaches itself to one of these4 ,in other words1 it ionises a molecule of the gas or confers its electric charge upon it4 ,the gaseous molecule may even be itself disrupted by impact of the electron1 if this is moving fast enough1 and left bereft of an electron4 ,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 derived4 ,similar ionisation under electric forces enters1 as we now believe1 into all the chemical effects progressing in the galvanic cell1 and1 indeed1 generally in ionised solutes4 ,an experiment will best illustrate the principles ,i wish to remind you of4 ,a clean aluminium plate1 carefully insulated by a sulphur support1 is faced by a sheet of copper-wire-gauze placed a couple of centimetres away from it4 ,the gauze is maintained at a high positive #bje potential by this dry pile4 ,a sensitive gold-leaf electroscope is attached to the aluminium plate1 and its image thrown upon the screen4 ,i now turn the light from this arc lamp upon the wire gauze1 through which it in part passes and shines upon the aluminium plate4 ,the electroscope at once charges up rapidly4 ,there is a liberation of negative electrons at the surface of the aluminium2 these1 under the attraction of the positive body1 are rapidly removed as ions1 and the electroscope charges up positively4 ,again1 if ,i simply electrify negatively this aluminium plate so that the leaves of the attached electroscope diverge widely1 and now expose it to the rays from the arc lamp1 the charge1 as you see1 is very rapidly dissipated4 ,with positive electrification of the aluminium there is no effect attendant on the illumination4 ,thus from the work of ,hertz and his successors we know that light1 and more particularly what we call actinic light1 is an effective means of setting free electrons from certain substances4 ,in short1 our photographic agent1 light1 has the power of expelling from certain substances the electron which is so potent a factor in most1 if not in all1 chemical effects4 ,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 wave1 but must turn to the probable bearing of this phenomenon on the familiar facts of photography4 ,i assume that the experiment ,i have shown you is the most #bjf fundamental photographic experiment which it is now in our power to make4 ,we must first ask from what substances can light liberate electrons4 ,there are many--metals as well as non-metals and liquids4 ,it is a very general phenomenon and must operate widely throughout nature4 ,but what chiefly concerns the present consideration is the fact that the haloid salts of silver are vigorously photo-electric1 and1 it is suggestive1 possess1 according to ,schmidt1 an activity in the descending order bromide1 chloride1 iodide4 ,this is1 in other words1 their order of activity as ionisers 7under the proper conditions7 when exposed to ultra-violet light4 ,photographers will recognise that this is also the order of their photographic sensitiveness4 ,another class of bodies also concerns our subject3 the special sensitisers used by the photographer to modify the spectral distribution of sensibility of the haloid salts1 e4g4 eosine1 fuchsine1 cyanine4 ,these again are electron-producers under light stimulus4 ,now it has been shown by ,stoletow1 ,hallwachs1 and ,elster and ,geitel that there is an intimate connection between photo-electric activity and the absorption of light by the substance1 and1 indeed1 that the particular wave-lengths absorbed by the substance are those which are effective in liberating the electrons4 ,thus we have strong reason for believing that the vigorous photo-electric activity displayed by the special sensitisers must be dependent upon their colour absorption4 ,you will recognise that this is just #bjg the connection between their photographic effects and their behaviour towards light4 ,there is yet another suggestive parallel4 ,i referred to the observation of ,sir ,james ,dewar as to the continued sensitiveness of the photographic film at the lowest attained extreme of temperature1 and drew the inference that the fundamental photographic action must be of intra-atomic nature1 and not dependent upon the vis viva of the molecule or atom4 ,in then seeking the origin of photographic action in photo-electric phenomena we naturally ask1 ,are these latter phenomena also traceable at low temperatures8 ,if they are1 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 activity4 ,i have quite recently1 with the aid of liquid air supplied to me from the laboratory of the ,royal ,dublin ,society1 tested the photo-sensibility of aluminium and also of silver bromide down to temperatures approaching that of the liquid air4 ,the mode of observation is essentially that of ,schmidt--what he terms his static method4 ,the substance undergoing observation is1 however1 contained at the bottom of a thin copper tube1 #e cm4 in diameter1 which is immersed to a depth of about #aj cm in liquid air4 ,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 pass4 ,the air within is very carefully dried by phosphorus #bjh pentoxide before the experiment4 ,the arc light is used as source of illumination4 ,it is found that a vigorous photo-electric effect continues in the case of the clean aluminium4 ,in the case of the silver bromide a distinct photo-electric effect is still observed4 ,i have not had leisure to make1 as yet1 any trustworthy estimate of the percentage effect at this temperature in the case of either substance4 ,nor have ,i determined the temperature accurately4 ,the latter may be taken as roughly about -#aej ,c1 ,sir ,james ,dewar's actual measilrements afforded twenty per cent4 of the normal photographic effect at -#ahj ,c4 and ten per cent4 at the temperature of -#beb4e ,c4 ,with this much to go upon1 and the important additional fact that the electronic discharge--as from the ,x-ray tube or from radium--generates the latent image1 ,i think we are fully entitled to suggest1 as a legitimate lead to experiment1 the hypothesis that the beginnings of photographic action involve an electronic discharge from the light-sensitive molecule2 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 haloid1 and it is upon these ionised atoms that the chemical effects of the developer are subsequently directed4 ,it may be that the liberated electrons ionise molecules not directly affected1 or it may be that in their liberation they disrupt complex molecules built up in the ripening of the #bji emulsion4 ,with the amount we have to go upon we cannot venture to particularise4 ,it will be said that such an action must be in part of the nature of a chemical effect4 ,this must be admitted1 and1 in so far as the rearrangement of molecular fabrics is involved1 the result will doubtless be controlled by temperature conditions4 ,the facts observed by ,sir ,james ,dewar support this4 ,but there is involved a fundamental process--the liberation of the electron by the electric force in the light wave1 which is a physical effect1 and which1 upon the hypothesis of its reality as a factor in forming the latent image1 appears to explain completely the outstanding photographic sensitiveness of the film at temperatures far below those at which chemical actions in general cease4 ,again1 we may assume that the electron--producing power of the special sensitiser or dye for the particular ray it absorbs is responsible1 or responsible in part1 for the special sensitiveness it confers upon the film4 ,sir ,wm4 ,abney has shown that these sensitisers are active even if laid on as a varnish on the sensitive surface and removed before development4 ,it must be remembered1 however1 that at temperatures of about -#ej these sensitisers lose much of their influence on the film2 as ,i have pointed out in a paper read before the ,photographic ,convention of #ahid4 ,it4 appears to me that on these views the curious phenomenon of recurrent reversals does not present a problem hopeless of explanation4 ,the process of photo- #baj ionisation constituting the latent image1 where the ion is probably not immediately neutralised by chemical combination1 presents features akin to the charging of a capacity--say a ,leyden jar4 ,there may be a rising potential between the groups of ions until ultimately a point is attained when there is a spontaneous neutralisation4 ,i may observe that the phenomena of reversal appear to indicate that the change in the silver bromide molecule1 whatever be its nature1 is one of gradually increasing intensity1 and finally attains a maximum when a return to the original condition occurs4 ,the maximum is the point of most intense developable image4 ,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 involved4 ,of great interest in all our considerations and theories is the recent work of ,wood on photographic reversal4 ,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 formation4 ,thus it appears that the sort of latent effect which is produced by pressure or friction is the least stable of any4 ,this may be reversed or wiped out by the application of any other known form of photographic stimulus4 ,thus an exposure to ,x-rays will obliterate it1 or a very brief exposure to light4 ,the latent image arising from ,x-rays is next in order of increasing stability4 ,light action will remove this4 ,third in order is a very brief light-shock or sudden flash4 ,this #baa cannot be reversed by any of the foregoing modes of stimulation1 but a long-continued undulatory stimulus1 as from lamp-light1 will reverse it4 ,last and most stable of all is the gradually built-up configuration due to long-continued light exposure4 ,this can only be reversed by overdoing it according to the known facts of recurrent reversal4 ,wood takes occasion to remark that these phenomena are in bad agreement with the strain theory of ,bose4 ,we have1 in fact1 but the one resource--the allotropic modification of the haloid--whereby to explain all these orders of stability4 ,it appears to me that the elasticity of the electronic theory is greater4 ,the state of the ionised system may be very various according as it arises from continued rhythmic effects or from unorganised shocks4 ,the ionisation due to ,x-rays or to friction will probably be quite unorganised1 that due to light more or less stable according to the gradual and gentle nature of the forces at work4 ,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 effects1 but that they rather fall in with what might be anticipated according to that theory4 ,when we look for further support to the views ,i have laid before you we are confronted with many difficulties4 ,i have not as yet detected any electronic discharge from the film under light stimulus4 ,this may be due to my defective experiments1 or to a fact noted by ,elster and ,geitel concerning the photo-electric properties of gelatin4 #bab ,they obtained a vigorous effect from ,balmain's luminous paint1 but when this was mixed in gelatin there was no external effect4 ,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 involved4 ,this conservative effect of the gelatin may be concerned with its efficacy as a sensitiser4 ,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 image4#a #a ,for a more detailed account of the subject1 and some ingenious extensions of the views expressed above1 see ,photo-,electricity1 by ,h4 ,stanley ,allen3 ,longmans1 ,green ,ca41 #aiac4 #bac ,,pleochroic ,,haloes #a ,,it is now well established that a helium atom is expelled from certain of the radioactive elements at the moment of transformation4 ,the helium atom or alpha ray leaves the transforming atom with a velocity which varies in the different radioactive elements1 but which is always very great1 attaining as much as #b x #aji cms4 per second2 a velocity which1 if unchecked1 would carry the atom round the earth in less than two seconds4 ,the alpha ray carries a positive charge of double the ionic amount4 ,when an alpha ray is discharged from the transforming element into a gaseous medium its velocity is rapidly checked and its energy absorbed4 ,a certain amount of energy is thus transferred from the transforming atom to the gas4 ,we recognise this energy in the gas by the altered properties of the latter2 chiefly by the fact that it becomes a conductor of electricity4 ,the mechanism by which this change is effected is in part known4 ,the atoms of the gas1 which appear to be freely penetrated by the alpha ray1 are so far dismembered as to yield charged electrons or ions2 the atoms remaining charged with an equal and opposite charge4 ,such a medium of #a ,being the ,huxley ,lecture1 delivered at the ,university of ,birmingham on ,october #cjth1 #aiab4 ,bedrock1 ,jan41 #aiac4 #bad free electric charges becomes a conductor of electricity by convection when an electromotive force is applied4 ,the gas also acquires other properties in virtue of its ionisation4 ,under certain conditions it may acquire chemical activity and new combinations may be formed or existing ones broken up4 ,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 agitation4 ,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 temperature4 ,we will review some of the facts ascertained4 ,the range or distance traversed in a gas at ordinary pressures is a few centimetres4 ,the following table1 compiled by ,geiger1 gives the range in air at the temperature of #ae ,c43 cms4 cms4 cms4 ,uranium #a - #b4ej ,thorium - #b4gb ,radioactinium #d4fj ,uranium #b - #b4ij ,radiothorium #c4hg ,actinium ,x - #d4dj ,ionium - #c4jj ,thorium ,x - #d4cj ,act ,emanation #e4gj ,radium - #c4cj ,th ,emanation #e4jj ,actinium ,a - #f4ej ,ra ,emanation #d4af ,thorium ,a - #e4gj ,actinium ,c - #e4dj ,radium ,a - #d4ge ,thorium ,c#a - #d4hj ,radium ,c - #f4id ,thorium ,c#b - #h4fj ,radium ,f - #c4gg ,it will be seen that the ray of greatest range is that proceeding from thorium ,c#b1 which reaches a distance of #h4f cms4 ,in the uranium family the fastest ray is #bae that of radium ,c4 ,it attains #f4id cms4 ,there is thus an appreciable difference between the ultimate distances traversed by the most energetic rays of the two families4 ,the shortest ranges are those of uranium #a and #b4 ,the ionisation effected by these rays is by no means uniform along the path of the ray4 ,by examining the conductivity of the gas at different points along the path of the ray1 the ionisation at these points may be determined4 ,at the limits of the range the ionisation ,fig4 #ac ceases4 ,in this manner the range is1 in fact1 determined4 ,the dotted curve 7,fig4 #ac7 depicts the recent investigation of the ionisation effected by a sheaf of parallel rays of radium ,c in air1 as determined by ,geiger4 ,the range is laid out horizontally in centimetres4 ,the numbers of ions are laid out vertically4 ,the remarkable nature of the results will be at once apparent4 ,we should have expected that the ray at the beginning of its path1 when its velocity and kinetic energy were greatest1 would have been more effective than towards the end of its range #baf when its energy had almost run out4 ,but the curve shows that it is just the other way4 ,the lagging ray1 about to resign its ionising properties1 becomes a much more efficient ioniser than it was at first4 ,the maximum efficiency is1 however1 in the case of a bundle of parallel rays1 not quite at the end of the range1 but about half a centimetre from it4 ,the increase to the maximum is rapid1 the fall from the maximum to nothing is much more rapid4 ,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 point4 ,but this evidently does not apply to the last #e or #aj mms4 of the range where the rate of ionisation and of the speed of the ray change most rapidly4 ,to what are the changing properties of the rays near the end of their path to be ascribed8 ,it is only recently that this matter has been elucidated4 ,when the alpha ray has sufficiently slowed down1 its power of passing right through atoms1 without appreciably experiencing any effects from them1 diminishes4 ,the opposing atoms begin to exert an influence on the path of the ray1 deflecting it a little4 ,the heavier atoms will deflect it most4 ,this effect has been very successfully investigated by ,geiger4 ,it is known as scattering4 ,the angle of scattering increases rapidly with the decrease of velocity4 ,now the effect of the scattering will be to cause some of the rays to complete their ranges #bag or1 more accurately1 to leave their direct line of advance a little sooner than others4 ,in the beautiful experiments of ,c4 ,t4 ,r4 ,wilson we are enabled to obtain ocular demonstration of the scattering4 ,the photograph 7,fig4 #ad471 which ,i owe to the kindness of ,mr4 ,wilson1 shows the deflection of the ray towards the end of its path4 ,in ,fig4 #ad this case the path of the ray has been rendered visible by the condensation of water particles under the influence of the ionisation2 the atmosphere in which the ray travels being in a state of supersaturation with water vapour at the instant of the passage of the ray4 ,it is evident that if we were observing the ionisation along a sheaf of parallel rays1 all starting with equal velocity1 #bah 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 range4 ,for1 in fact1 some of the rays complete their work of ionising at points in the gas before the end is reached4 ,this is the cause1 or at least an important contributory cause1 of the decline in the ionisation near the end of the range1 when the effects of a bundle of rays are being observed4 ,the explanation does not suggest that the ionising power of any one ray is actually diminished before it finally ceases to be an alpha ray4 ,the full line in ,fig4 #ac gives the ionisation curve which it may be expected would be struck out by a single alpha ray4 ,in it the ionisation goes on increasing till it abruptly ceases altogether1 with the entire loss of the initial kinetic energy of the particle4 ,a highly remarkable fact was found out by ,bragg4 ,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 atom4 ,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 air4 ,the less the ratio the greater is the stopping power4 ,the stopping power of a substance is proportional to the square root of its atomic weight4 ,the stopping power of an atom is not altered if it is in chemical union with another atom4 ,the atomic weight is the one quality of importance4 ,the physical #bai state1 whether the element is in the solid1 liquid or gaseous state1 is unimportant4 ,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 molecule4 ,this is the additive law1 and it obviously enables us to calculate what the range in any substance of known chemical composition and density will be1 compared with the range in air4 ,this is of special importance in connection with phenomena we have presently to consider4 ,it means that1 knowing the chemical composition and density of any medium whatsoever1 solid1 liquid or gaseous1 we can calculate accurately the distance to which any particular alpha ray will penetrate4 ,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 another4 ,the retardation of the alpha ray in the atom is not affected4 ,this valuable additive law1 however1 cannot be applied in strictness to the amount of ionisation attending the ray4 ,the form of the molecule1 or more generally its volume1 may have an influence upon this4 ,bragg draws the conclusion1 from this fact as well as from the notable increase of ionisation with loss of speed1 that the ionisation is dependent upon the time the ray spends in the molecule4 ,the energy of the ray is1 indeed1 found to be less efficient in producing ionisation in the smaller atomm4 #bbj ,before leaving our review of the general laws governing the passage of alpha rays through matter1 another point of interest must be referred to4 ,we have hitherto spoken in general terms of the fact that ionisation attends the passage of the ray4 ,we have said nothing as to the nature of the ionisation so produced4 ,but in point of fact the ionisation due to an alpha ray is sui generis4 ,a glance at one of ,wilson's photographs 7,fig4 #ad47 illustrates this4 ,the white streak of water particles marks the path of the ray4 ,the ions produced are evidently closely crowded along the track of the ray4 ,they have been called into existence in a very minute instant of time4 ,now we know that ions of opposite sign if left to themselves recombine4 ,the rate of recombination depends upon the product of the number of each sign present in unit volume4 ,here the numbers are very great and the volume very small4 ,the ionic density is therefore high1 and recombination very rapidly removes the ions after they are formed4 ,we see here a peculiarity of the ionisation effected by alpha rays4 ,it is linear in distribution and very local4 ,much of the ionisation in gases is again undone by recombination before diffusion leads to the separation of the ions4 ,this initial recombination is greatest towards the end of the path of the ray where the ionisation is a maximum4 ,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 investigated4 #bba ,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 atom4 ,let us glance briefly at what we have learned4 ,the radioactive atom in sinking to a lower atomic weight casts out with enormous velocity an atom of helium4 ,it thus loses a definite portion of its mass and of its energy4 ,helium which is chemically one of the most inert of the elements1 is1 when possessed of such great kinetic energy1 able to penetrate and ionise the atoms which it meets in its path4 ,it spends its energy in the act of ionising them1 coming to rest1 when it moves in air1 in a few centimetres4 ,its initial velocity depends upon the particular radioactive element which has given rise to it4 ,the length of its path is therefore different according to the radioactive element from which it proceeds4 ,the retardation which it experiences in its path depends entirely upon the atomic weight of the atoms which it traverses4 ,as it advances in its path its effectiveness in ionising the atom rapidly increases and attains a very marked maximum4 ,in a gas the ions produced being much crowded together recombine rapidly2 so rapidly that the actual ionisation may be quite concealed unless a sufficiently strong electric force is applied to separate them4 ,such is a brief summary of the climax of radioactive discovery3--the birth1 life and death of the alpha ray4 ,its advent into ,science has altered fundamentally our conception of #bbb matter4 ,it is fraught with momentous bearings upon ,geological ,science4 ,how the work of the alpha ray is sometimes recorded visibly in the rocks and what we may learn from that record1 ,i propose now to bring before you4 ,in certain minerals1 notably the brown variety of mica known as biotite1 the microscope reveals minute circular marks occurring here and there1 quite irregularly4 ,the most usual appearance is that of a circular area darker in colour than the surrounding mineral4 ,the radii of these little disc-shaped marks when well defined are found to be remarkably uniform1 in some cases four hundredths of a millimetre and in others three hundredths1 about4 ,these are the measurements in biotite4 ,in other minerals the measurements are not quite the same as in biotite4 ,such minute objects are quite invisible to the naked eye4 ,in some rocks they are very abundant1 indeed they may be crowded together in such numbers as to darken the colour of the mineral containing them4 ,they have long been a mystery to petrologists4 ,close examination shows that there is always a small speck of a foreign body at the centre of the circle1 and it is often possible to identify the nature of this central substance1 small though it be4 ,most generally it is found to be the mineral zircon4 ,now this mineral was shown by ,strutt to contain radium in quantities much exceeding those found in ordinary rock substances4 #bbc ,some other mineral may occasionally form the nucleus1 but we never find any which is not known to be specially likely to contain a radioactive substance4 ,another circumstance we notice4 ,the smaller this central nucleus the more perfect in form is the darkened circular area surrounding it4 ,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 #j4jcc mm4 ,it may sometimes be #j4jdj mm4 ,these are always the measurements in biotite4 ,in other minerals the radii are a little different4 ,we see in the photograph 7,pl4 ,,xxiii1 lower figure71 much magnified1 a halo contained in biotite4 ,we are looking at a region in a rock-section1 the rock being ground down to such a thickness that light freely passes through it4 ,the biotite is in the centre of the field4 ,quartz and felspar surround it4 ,the rock is a granite4 ,the biotite is not all one crystal4 ,two crystals1 mutually inclined1 are cut across4 ,the halo extends across both crystals1 but owing to the fact that polarised light is used in taking the photograph it appears darker in one crystal than in the other4 ,we see the zircon which composes the nucleus4 ,the fine striated appearance of the biotite is due to the cleavage of that mineral1 which is cut across in the section4 ,the question arises whether the darkened area surrounding the zircon may not be due to the influence of the radioactive substances contained in the zircon4 ,the #bbd extraordinary uniformity of the radial measurements of perfectly formed haloes 7to use the name by which they have long been known7 suggests that they may be the result of alpha radiation4 ,for in that case1 as we have seen1 we can at once account for the definite radius as simply representing the range of the ray in biotite4 ,the furthest-reaching ray will define the radius of the halo4 ,in the case of the uranium family this will be radium ,c1 and in the case of thorium it will be thorium ,c4 ,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 radiation2 for we can calculate what the range of these rays will be in biotite1 availing ourselves of ,bragg's additive law1 already referred to4 ,when we make this calculation we find that radium ,c just penetrates #j4jcc mm4 and thorium ,c #j4jdj mm4 ,the proof is complete that we are dealing with the effects of alpha rays4 ,observe now that not only is the coincidence of measurement and calculation a proof of the view that alpha radiation has occasioned the halo1 but it is a very complete verification of the important fact stated by ,bragg1 that the stopping power depends solely on the atomic weight of the atoms traversed by the ray4 ,we have seen that our examination of the rocks reveals only the two sorts of halo3 the radium halo and the thorium halo4 ,this is not without teaching4 ,for why not find an actinium halo8 ,now ,rutherford long ago suggested that this element and its derivatives were #bbe probably an offspring of the uranium family2 a side branch1 as it were1 in the formation of which relatively few transforming atoms took part4 ,on ,rutherford's theory then1 actinium should always accompany uranium and radium1 but in very subordinate amount4 ,the absence of actinium haloes clearly supports this view4 ,for if actinium was an independent element we would be sure to find actinium haloes4 ,the difference in radius should be noticeable4 ,if1 on the other hand1 actinium was always associated with uranium and radium1 then its effects would be submerged in those of the much more potent effects of the uranium series of elements4 ,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 circular1 but spherical4 ,this is so4 ,there is no such thing as a disc-shaped halo4 ,the halo is a spherical volume containing the radioactive nucleus at its centre4 ,the true radius of the halo may1 therefore1 only be measured on sections passing through the nucleus4 #bbf ,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-sphere4 ,such a diagram is seen in ,fig4 #ae4 ,it shows to relatively correct scale the limiting range of all the alpha-ray producing members of the uranium and thorium families4 ,we know that each member of a family will exist in equilibrium amount within the nucleus possessing the parent element4 ,each alpha ray leaving the nucleus will just attain its range and then cease to affect the mica4 ,within the halosphere1 there must be1 therefore1 the accumulated effects of the influences of all the rays4 ,each has its own sphere of influence1 and the spheres are all concentric4 ,the radii in biotite of the several spheres are given in the following table ,,uranium ,,family4 ,radium ,c - #j4jccj mm4 ,radium ,a - #j4jbbd mm4 ,ra ,emanation - #j4jaif mm4 ,radium ,f - #j4jagg mm4 ,radium - #j4jaef mm4 ,ionium - #j4jada mm4 ,uranium #a - #j4jacg mm4 ,uranium #b - #j4jaah mm4 ,,thorium ,,family4 ,thorium ,,ce - #j4jdj mm4 ,thorium ,a - #j4jbf mm4 ,th ,emanation - #j4jbc mm4 ,thorium ,ci - #j4jbb mm4 ,thorium ,x - #j4jbj mm4 ,radiothorium - #j4aai mm4 ,thorium - #j4jac mm4 ,in the photograph 7,pl4 ,,xxiv1 lower figure71 we see a uranium and a thorium halo in the same crystal of mica4 ,the mica is contained in a rock-section and is cut across the cleavage4 ,the effects of thorium ,ca are clearly shown #bbg as a lighter border surrounding the accumulated inner darkening due to the other thorium rays4 ,the uranium halo 7to the right7 similarly shows the effects of radium ,c1 but less distinctly4 ,haloes which are uniformly dark all over as described above are1 in point of fact1 over-exposed2 to borrow a familiar photographic term4 ,haloes are found which show much beautiful internal detail4 ,too vigorous action obscures this detail just as detail is lost in an over-exposed photograph4 ,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 trace4 ,beginning at the most under-exposed haloes we find circular dark marks having the radius #j4jab or #j4jac mm4 ,these haloes are due to uranium1 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 rays4 ,then we find haloes carried out to the radii #j4jaf1 #j4jah and #j4jai mm4 ,the last sometimes show very beautiful outer rings having radial dimensions such as would be produced by radium ,a and radium ,c4 ,finally we may have haloes in which interior detail is lost so far out as the radius due to emanation or radium ,a1 while outside this floats the ring due to radium ,c4 ,certain variations of these effects may occur1 marking1 apparently1 different stages of exposure4 ,plates ,,xxiii and ,,xxiv 7upper figure7 illustrate some of these stages2 #bbh the latter photograph being greatly enlarged to show clearly the halo-sphere of radium ,a4 ,in most of the cases mentioned above the structure evidently shows the existence of concentric spherical shells of darkened biotite4 ,this is a very interesting fact4 ,for it proves that in the mineral the alpha ray gives rise to the same increased ionisation towards the end of its range1 as ,bragg determined in the case of gases4 ,and we must conclude that the halo in every case grows in this manner4 ,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 mineral4 ,this more feeble ionisation is1 near the nucleus1 enhanced in its effects by the fact that there all the rays combine to increase the ionisation and1 moreover1 the several tracks are there crowded by the convergency to the centre4 ,hence the most elementary haloes seldom show definite rings due to uranium1 etc41 but appear as embryonic disc-like markings4 ,the photographs illustrate many of the phases of halo development4 ,rutherford succeeded in making a halo artificially by compressing into a capillary glass tube a quantity of the emanation of radium4 ,as the emanation decayed the various derived products came into existence and all the several alpha rays penetrated the glass1 darkening the walls of the capillary out to the limit of the range of radium ,c in glass4 ,plate ,,xxv shows a magnified section of the #bbi tube4 ,the dark central part is the capillary4 ,the tubular halo surrounds it4 ,this experiment has1 however1 been anticipated by some scores of millions of years1 for here is the same effect in a biotite crystal 7,pl4 ,,xxv74 ,along what are apparently tubular passages or cracks in the mica1 a solution1 rich in radioactive substances1 has moved2 probably during the final consolidation of the granite in which the mica occurs4 ,a continuous and very regular halo has developed along these conduits4 ,a string of halo-spheres may lie along such passages4 ,we must infer that solutions or gases able to establish the radioactive nuclei moved along these conduits1 and we are entitled to ask if all the haloes in this biotite are not1 in this sense1 of secondary origin4 ,there is1 ,i may add1 much to support such a conclusion4 ,the widespread distribution of radioactive substances is most readily appreciated by examination of sections of rocks cut thin enough for microscopic investigation4 ,it is1 indeed1 difficult to find1 in the older rocks of granitic type1 mica which does not show haloes1 or traces of haloes4 ,often we find that every one of the inclusions in the mica--that is1 every one of the earlier formed substances--contain radioactive elements1 as indicated by the presence of darkened borders4 ,as will be seen presently the quantities involved are generally vanishingly small4 ,for example it was found by direct determination that in one gram of the halo-rich mica of ,co4 ,carlow there was rather less than twelve billionths of a gram of radium1 ,we are #bcj entitled to infer that other rare elements are similarly widely distributed but remain undetectable because of their more stable properties4 ,it must not be thought that the under-exposed halo is a recent creation4 ,by no means4 ,all are old1 appallingly old2 and in the same rock all are1 probably1 of the same1 or neatly the same1 age4 ,the under-exposure is simply due to a lesser quantity of the radioactive elements in the nucleus4 ,they are under-exposed1 in short1 not because of lesser duration of exposure1 but because of insufficient action2 as when in taking a photograph the stop is not open enough for the time of the exposure4 ,the halo has1 so far1 told us that the additive law is obeyed in solid media1 and that the increased ionisation attending the slowing down of the ray obtaining in gases1 also obtains in solids2 for1 otherwise1 the halo would not commence its development as a spherical shell or envelope4 ,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 solid4 ,in the former1 initial recombination may obscure the intense ionisation near the end of the range4 ,we can only detect the true end-effects by artificially separating the ions by a strong electric force4 ,if this recombination happened in the mineral we should not have the concentric spheres so well defined as we see them to be4 ,what1 then1 hinders the initial recombination in the solid8 ,the answer probably is that the newly formed #bca ion is instantly used up in a fresh chemical combination4 ,nor is it free to change its place as in the gas4 ,there is simply a new equilibrium brought about by its sudden production4 ,in this manner the conditions in the complex molecule of biotite1 tourmaline1 etc41 may be quite as effective in preventing initial recombination as the most effective electric force we could apply4 ,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 halo4 ,that the shading of the rings reproduces the form of the ,bragg curve1 projected1 as it were1 upon the line of advance of the ray and reproduced in depth of shading1 shows that in yet another particular the alpha ray behaves much the same in the solid as in the gas4 ,a careful examination of the outer edge of the circles always reveals a steep but not abrupt cessation of the action of the ray4 ,now ,geiger has investigated and proved the existence of scattering of the alpha ray by solids4 ,we may1 therefore1 suppose with much probability that there is the same scattering within the mineral near the end of the range4 ,the heavy iron atom of the biotite is1 doubtless1 chiefly responsible for this in biotite haloes4 ,i may observe that this shading of the outer bounding surface of the sphere of action is found however minute the central nucleus4 ,in the case of a nucleus of considerable size another effect comes in which tends to produce an enhanced shading4 ,this will #bcb result if rays proceed from different depths in the nucleus4 ,if the nucleus were of the same density and atomic weight as the surrounding mica1 there would be little effect4 ,but its density and molecular weight are generally greater1 hence the retardation is greater1 and rays proceeding from deep in the nucleus experience more retardation than those which proceed from points near to the surface4 ,the distances reached by the rays in the mica will vary accordingly1 and so there will be a gradual cessation of the effects of the rays4 ,the result of our study of the halo may be summed up in the statement that in nearly every particular we have the phenomena1 which have been measured and observed in the gas1 reproduced on a minute scale in the halo4 ,initial recombination seems1 however1 to be absent or diminished in effectiveness2 probably because of the new stability instantly assumed by the ionised atoms4 ,one of the most interesting points about the halo remains to be referred to4 ,the halo is always uniformly darkened all round its circumference and is perfectly spherical4 ,sections1 whether taken in the plane of cleavage of the mica or across it1 show the same exactly circular form1 and the same radius4 ,of course1 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 elliptical4 ,the fact that there is no measurable ellipticity is1 ,i think1 one which on first consideration would not be expected4 #bcc ,for what are the conditions attending the passage of the ray in a medium such as mica8 ,according to crystallographic conceptions we have here an orderly arrangement of molecules1 the units composing the crystal being alike in mass1 geometrically spaced1 and polarised as regards the attractions they exert one upon another4 ,mica1 more especially1 has the cleavage phenomenon developed to a degree which transcends its development in any other known substance4 ,we can cleave it and again cleave it till its flakes float in the air1 and we may yet go on cleaving it by special means till the flakes no longer reflect visible light4 ,and not less remarkable is the uniplanar nature of its cleavage4 ,there is little cleavage in any plane but the one1 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 others4 ,in such a medium beyond all others we must look with surprise upon the perfect sphere struck out by the alpha rays1 because it seems certain that the cleavage is due to lesser attraction1 and1 probably1 further spacing of the molecules1 in a direction perpendicular to the cleavage4 ,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 paths4 ,if this is so1 we seem left to conclude that1 in spite of its unequal and polarised attractions1 there is equal retardation and equal ionisation in the molecule in whatever #bcd direction it is approached4 ,or1 again1 if the encounters indeed differ in number1 then some compensating effect must exist whereby a direction of lesser linear density involves greater stopping power in the molecule encountered1 and vice versa4 ,the nature of the change produced by the alpha rays is unknown4 ,but the formation of the halo is not1 at least in its earlier stages1 attended by destruction of the crystallographic and optical properties of the medium4 ,the optical properties are unaltered in nature but are increased in intensity4 ,this applies till the halo has become so darkened that light is no longer transmitted under the conditions of thickness obtaining in rock sections4 ,it is well known that there is in biotite a maximum absorption of a plane-polarised light ray1 when the plane of vibration coincides with the plane of cleavage4 ,a section across the cleavage then shows a maximum amount of absorption4 ,a halo seen on this section simply produces this effect in a more intense degree4 ,this is well shown in ,plate ,,xxiii 7lower figure71 on a portion of the halo-sphere4 ,the descriptive name ,pleochroic ,halo has originated from this fact4 ,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 medium4 ,the increased absorption is probably associated with some change in the chemical state of the iron present4 ,haloes are1 ,i believe1 not found in minerals from which this #bce element is absent4 ,one thing is quite certain4 ,the colouration is not due to an accumulation of helium atoms1 i4e4 of spent alpha rays4 ,the evidence for this is conclusive4 ,if helium was responsible we should have haloes produced in all sorts of colourless minerals4 ,now we sometimes see zircons in felspars and in quartz1 etc41 but in no such case is a halo produced4 ,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 quartz1 although we know that the rays must pass freely across the boundary4 ,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 helium4 ,there is1 finally1 no reason to suppose that the imprisoned helium would exhibit such a colouration1 or1 indeed1 any at all4 ,i have already referred to the great age of the halo4 ,haloes are not found in the younger igneous rocks4 ,it is probable that a halo less than a million years old has never been seen4 ,this1 prim facie1 indicates an extremely slow rate of formation4 ,and our calculations quite support the conclusions that the growth of a halo1 if this has been uniform1 proceeds at a rate of almost unimaginable slowness4 ,let us calculate the number of alpha rays which may have gone to form a halo in the ,devonian granite of ,leinster4 #bcf ,it is common to find haloes developed perfectly in this granite1 and having a nucleus of zircon less than #e x #aj-d cms4 in diameter4 ,the volume of zircon is #fe x #aj-ab c4cs4 and the mass #c x #aj-aj grm42 and if there was in this zircon #aj-h grm4 radium per gram 7a quantity about five times the greatest amount measured by ,strutt71 the mass of radium involved is #c x #aj-ah grm4 ,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 #c4d x #ajaj1 we find that three rays are shot from the nucleus in a year4 ,if1 now1 geological time since the ,devonian is #ej millions of years1 then #aej millions of rays built up the halo4 ,if geological time since the ,devonian is #djj millions of years1 then #a1bjj millions of alpha rays are concerned in its genesis4 ,the number of ions involved1 of course1 greatly exceeds these numbers4 ,a single alpha ray fired from radium ,c will produce #b4cg x #aje ions in air4 ,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 materials4 ,thus a zircon nucleus with a diameter of but #c4d x #aj-d cms4 formed a halo strongly darkened within1 and showing radium ,a and radium ,c as clear smoky rings4 ,such a nucleus1 on the assumption made above as to its radium content1 expels one ray in a year4 ,but1 again1 haloes are observed with less blackened pupils and with faint ring due to radium ,c1 formed round nuclei #bcg of rather less than #b x #aj-d cms4 diameter4 ,such nuclei would expel one ray in five years4 ,and even lesser nuclei will generate in these old rocks haloes with their earlier characteristic features clearly developed4 ,in the case of the most minute nuclei1 if my assumption as to the uranium content is correct1 an alpha ray is expelled1 probably1 no oftener than once in a century2 and possibly at still longer intervals4 ,the equilibrium amount of radium contained in some nuclei may amount to only a few atoms4 ,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 means4 ,but the delicacy of the observation is not adequately set forth in this statement4 ,we can not only tell the nature of the radioactive family with which we are dealing2 but we can recognise the presence of some of its constituent members4 ,i may say that it is not probable the zircons are richer in radium than ,i have assumed4 ,my assumption involves about #c per cent4 of uranium4 ,i know of no analyses ascribing so great an amount of uranium to zircon4 ,the variety cyrtolite has been found to contain half this amount1 about4 ,but even if we doubled our estimate of radium content1 the remarkable nature of our conclusions is hardly lessened4 ,it may appear strange that the ever-interesting question of the ,earth's age should find elucidation from the #bch study of haloes4 ,nevertheless the subjects are closely connected4 ,the circumstances are as follows4 ,geologists have estimated the age of the ,earth since denudation began1 by measurements of the integral effects of denudation4 ,these methods agree in showing an age of about rob years4 ,on the other hand1 measurements have been made of the accumulation in minerals of radioactive dbris--the helium and lead--and results obtained which1 although they do not agree very well among themselves1 are concordant in assigning a very much greater age to the rocks4 ,if the radioactive estimate is correct1 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 past4 ,such a state of things is absolutely unaccountable4 ,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 rocks4 ,both the methods referred to of finding the age assume the principle of uniformity4 ,the geologist contends for uniformity throughout the past physical history of the ,earth4 ,the physicist claims the like for the change-rates of the radioactive elements4 ,now the study of the rocks enables us to infer something as to the past history of our ,globe4 ,nothing is1 on the other hand1 known respecting the origin of uranium or thorium--the parent radioactive bodies4 ,and while not questioning the law #bci and regularity which undoubtedly prevail in the periods of the members of the radioactive families1 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 be4 ,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 rocks4 ,such atoms might have been collateral in origin with uranium from some antecedent element4 ,like helium1 lead may be a derivative from more than one sequence of radioactive changes4 ,in the present state of our knowledge the possibilities are many4 ,the rate of change is known to be connected with the range of the alpha ray expelled by the transforming element2 and the conformity of the halo with our existing knowledge of the ranges is reason for assuming that1 whatever the origin of the more active associate of uranium1 this passed through similar elemental changes in the progress of its disintegration4 ,there may1 however1 have been differences in the ranges which the halo would not reveal4 ,it is remarkable that uranium at the present time is apparently responsible for two alpha rays of very different ranges4 ,if these proceed from different elements1 one should be faster in its change rate than the other4 ,some guidance may yet be forthcoming from the study of the more obscure problems of radioactivity4 ,now it is not improbable that the halo may contribute directly to this discussion4 ,we can evidently attack #bdj the biotite with a known number of alpha rays and determine how many are required to produce a certain intensity of darkening1 corresponding to that of a halo with a nucleus of measurable dimensions4 ,on certain assumptions1 which are correct within defined limits1 we can calculate1 as ,i have done above1 the number of rays concerned in forming the halo4 ,in doing so we assume some value for the age of the halo4 ,let us take the maximum radioactive value4 ,a halo originating in ,devonian times may attain a certain central blackening from the effects of1 say1 rob rays4 ,but now suppose we find that we cannot produce the same degree of blackening with this number of rays applied in the laboratory4 ,what are we to conclude8 ,i think there is only the one conclusion open to us2 that some other source of alpha rays1 or a faster rate of supply1 existed in the past4 ,and this conclusion would explain the absence of haloes from the younger rocks2 which1 in view of the vast range of effects possible in the development of haloes1 is1 otherwise1 not easy to account for4 ,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 rocks4 ,it is now being carried out by ,professor ,rutherford under reliable conditions4 ,finally1 there is one very certain and valuable fact to be learned from the halo4 ,the halo has established the extreme rarity of radioactivity as an atomic phenomenon4 ,one and all of the speculations as to #bda the slow breakdown of the commoner elements may be dismissed4 ,the halo shows that the mica of the rocks is radioactively sensitive4 ,the fundamental criterion of radioactive change is the expulsion of the alpha ray4 ,the molecular system of the mica and of many other minerals is unstable in presence of these rays1 just as a photographic plate is unstable in presence of light4 ,moreover1 the mineral integrates the radioactive effects in the same way as a photographic salt integrates the effects of light4 ,in both cases the feeblest activities become ultimately apparent to our inspection4 ,we have seen that one ray in each year since the ,devonian period will build the fully formed halo3 an object unlike any other appearance in the rocks4 ,and we have been able to allocate all the haloes so far investigated to one or the other of the known radioactive families4 ,we are evidently justified in the belief that had other elements been radioactive we must either find characteristic haloes produced by them1 or else find a complete darkening of the mica4 ,the feeblest alpha rays emitted by the relatively enormous quantities of the prevailing elements1 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 minerals4 ,and thus we are safe in concluding that the common elements1 and1 indeed1 many which would be called rare1 are possessed of a degree of stability which has preserved them un #bdb changed since the beginning of geological time4 ,each unaffected flake of mica is1 thus1 unassailable proof of a fact which but for the halo would1 probably1 have been for ever beyond our cognisance4 ,,the ,,use ,,of ,,radium ,,in ,,medicine #a ,,it has been unfortunate for the progress of the radioactive treatment of disease that its methods and claims involve much of the marvellous4 ,up till recently1 indeed1 a large part of radioactive therapeutics could only be described as bordering on the occult4 ,it is not surprising that when1 in addition to its occult and marvellous characters1 claims were made on its behalf which in many cases could not be supported1 many medical men came to regard it with a certain amount of suspicion4 ,today1 ,i believe1 we are in a better position4 ,i think it is possible to ascribe a rational scientific basis to its legitimate claims1 and to show1 in fact1 that in radioactive treatment we are pursuing methods which have been already tried extensively and found to be of definite value2 and that new methods differ from the old mainly in their power and availability1 and little1 or not at all1 in kind4 ,let us briefly review the basis of the science4 ,radium is a metallic element chemically resembling barium4 ,it #a ,a ,lecture to ,postgraduate ,students of ,medicine in connection with the founding of the ,dublin ,radium ,institute1 delivered in the ,school of ,physic in ,ireland1 ,trinity ,college1 on ,october #bnd1 #aiad #bdd possesses1 however1 a remarkable property which barium does not4 ,its atoms are not equally stable4 ,in a given quantity of radium a certain very small percentage of the total number of atoms present break up per second4 ,by breaking up we mean their transmutation to another element4 ,radium1 which is a solid element under ordinary conditions1 gives rise by transmutation to a gaseous element--the emanation of radium4 ,the new element is a heavy gas at ordinary temperatures and1 like other gases1 can be liquified by extreme cold4 ,the extraordinary property of transmutation is entirely automatic4 ,no influence which chemist or physicist can apply can affect the rate of transformation4 ,the emanation inherits the property of instability1 but in its case the instability is more pronounced4 ,a relatively large fraction of its atoms transmute per second to a solid element designated ,radium ,a4 ,in turn this new generation of atoms breaks up--even faster than the emanation--becoming yet another element with specific chemical properties4 ,and so on for a whole sequence of transmutations1 till finally a stable substance is formed1 identical with ordinary lead in chemical and physical properties1 but possessing a slightly lower atomic weight4 ,the genealogy of the radium series of elements shows that radium is not the starting point4 ,it possesses ancestors which have been traced back to the element uranium4 ,now what bearing has this series of transmutations #bde upon medical science8 ,radium or emanation1 c41 are not in the ,pharmacopoeia as are1 say1 arsenic or bismuth4 ,the whole medicinal value of these elements resides in the very wonderful phenomena of their radiations4 ,they radiate in the process of transmuting4 ,the changing atom may radiate a part of its own mass4 ,the alpha-ray 7a-ray7 is such a material ray4 ,it is an electrified helium atom cast out of the parent atom with enormous velocity--such a velocity as would carry it1 if not impeded1 all round the earth in two seconds4 ,all alpha-rays are positively electrified atoms of the element helium1 which thereby is shown to be an integral constituent of many elements4 ,the alpha-ray is not of much value to medical science1 for1 in spite of its great velocity1 it is soon stopped by encounter with other atoms4 ,it can penetrate only a minute fraction of a millimetre into ordinary soft tissues4 ,we shall not further consider it4 ,transmuting atoms give out also material rays of another kind3 the -rays4 ,the -ray is in mass but a very small fraction of1 even1 a hydrogen atom4 ,its speed may approach that of light4 ,as cast out by radioactive elements it starts with speeds which vary with the element1 and may be from one-third to nine-tenths the velocity of light4 ,the -ray is negatively electrified4 ,it has long been known to science as the electron4 ,it is also identical with the cathode ray of the vacuum tube4 #bdf ,another and quite different kind of radiation is given out by many of the transmuting elements3--the y-ray4 ,this is not material1 it is ethereal4 ,it is known now with certainty that the y-ray is in kind identical with light1 but of very much shorter wave length than even the extreme ultraviolet light of the solar spectrum4 ,the y-ray is flashed from the transmuting atom along with the -ray4 ,it is identical in character with the x-ray but of even shorter wave length4 ,there is a very interesting connection between the y-ray and the -ray which it is important for the medical man to understand--as far as it is practicable on our present knowledge4 ,when y-rays or x-rays fall on matter they give rise to -rays4 ,the mechanism involved is not known but it is possibly a result of the resonance of the atom1 or of parts of it1 to the short light waves4 ,and it is remarkable that the y-rays which1 as we have seen1 are shorter and more penetrating waves than the x-rays1 give rise to -rays possessed of greater velocity and penetration than -rays excited by the x-rays4 ,indeed the -rays originated by y-rays may attain a velocity nearly approaching that of light and as great as that of any -rays emitted by transmuting atoms4 ,again there is demonstrable evidence that -rays impinging on matter may give rise to y-rays4 ,the most remarkable demonstration of this is seen in the x-ray tube4 ,here the x-rays originate where the stream of - or cathode-rays #bdg are arrested on the anode4 ,but the first relation is at present of most importance to us--i4e4 that the y-or x-rays give rise to -rays4 ,this relation gives us additional evidence of the identity of the physical effects of y-1 x-1 and light-rays --using the term light rays in the usual sense of spectral rays4 ,for it has long been known that light waves liberate electrons from atoms4 ,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 liberation4 ,the whole science of photo-electricity centres round this phenomenon4 ,the action of light on the photographic plate1 as well as many other physical and chemical phenomena1 find an explanation in this liberation of the electron by the light wave4 ,here1 then1 we have spectral light waves liberating electrons--i4e4 very minute negatively-charged particles1 and we find that1 as we use shorter light waves1 the initial velocity of these particles increases4 ,again1 we have x-rays which are far smaller in wave length than spectral light1 liberating much faster negatively electrified particles4 ,finally1 we have y-rays--the shortest nether waves of all-liberating negative particles of the highest velocity known4 ,plainly the whole series of phenomena is continuous4 ,we can now look closer at the actions involved in the therapeutic influence of the several rays and in #bdh this way1 also1 see further the correlation between what may be called photo-therapeutics and radioactive therapeutics4 ,the -ray1 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 atom1 is an ionising agent of wonderful power4 ,what is meant by this8 ,in its physical aspect this means that the atoms through which it passes acquire free electric charges2 some becoming positive1 some negative4 ,this can only be due to the loss of an electron by the affected atom4 ,the loss of the small negative charge carried in the electron leaves the atom positively electrified or creates a positive ion4 ,the fixing of the wandering electron to a neutral atom creates a negative ion4 ,before further consideration of the importance of the phenomenon of ionisation we must fix in our minds that the agent1 which brings this about1 is the -ray4 ,there is little evidence that the y-ray can directly create ions to any large extent4 ,but the action of liberating high-speed -rays results in the creation of many thousands of ions by each -ray liberated4 ,as an agent in the hands of the medical man we must regard the y-ray as a light wave of extremely penetrating character1 which creates high-speed -rays in the tissues which it penetrates1 these -rays being most potent ionising agents4 ,the -rays directly obtained from radioactive atoms assist in the work of ionisation4 -rays do not #bdi penetrate far from their source4 ,the fastest of them would not probably penetrate one centimetre in soft tissues4 ,we must now return to the phenomenon of ionisation4 ,ionisation is revealed to observation most conspicuously when it takes place in a gas4 ,the and - electric charges on the gas particles endow it with the properties of a conductor of electricity1 the ions moving freely in one direction and the - ions in the opposite direction under an electric potential4 ,but there are effects brought about by ionisation of more importance to the medical man than this4 ,the chemist has long come to recognise that in the ion he is concerned with the inner mechanism of a large number of chemical phenomena4 ,for with the electrification of the atom attractive and repulsive forces arise4 ,we can directly show the chemical effects of the ionising -rays4 ,water exposed to their bombardment splits up into hydrogen and oxygen4 ,and1 again1 the separated atoms may be in part recombined under the influence of the radiation4 ,ammonia splits up into hydrogen and nitrogen4 ,carbon dioxide forms carbon1 carbon monoxide1 and oxygen2 hydrochloric acid forms chlorine and hydrogen4 ,in these cases1 also1 recombination can be partially effected by the rays4 ,we can be quite sure that within the complex structure of the living cell the ionising effects which everywhere accompany the -rays must exert a profound influence4 ,the sequence of chemical events which as yet seem #bej beyond the ken of science and which are involved in metabolism cannot fail to be affected4 ,any1 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 cell4 ,it is easy to see that the feeble radiation should produce the one effect1 the strong the other4 ,in a similar way by a moderate light stimulus we create the latent image in the photographic plate2 by an intense light we again destroy this image4 ,the inner mechanism in this last case can be logically stated4#a ,there is plainly a true physical basis here for the efficacy of radioactive treatment and1 what is more1 we find when we examine it1 that it is in kind not different from that underlying treatment by spectral radiations4 ,but in degree it is very different and here is the reason for the special importance of radioactivity as a therapeutic agent4 ,the ,finsen light is capable of influencing the soft tissues to a short depth only4 ,the reason is that the wave length of the light used is too great to pass without rapid absorption through the tissues2 and1 further1 the electrons it gives rise to--i4e4 the -rays it liberates--are too slow-moving to be very efficient ionisers4 ,x-rays penetrate in some cases quite freely and give rise to much faster and more powerful -rays #a ,see ,the ,latent ,image1 p4 #bjb4 #bea than can the ,finsen light4 ,but far more penetrating than x-rays are the y-rays emitted in certain of the radioactive changes4 ,these give rise to -rays having a velocity approximate to that of light4 ,the y-rays are1 therefore1 very penetrating and powerfully ionising light waves2 light waves which are quite invisible to the eye and can beam right through the tissues of the body4 ,to the mind's eye only are they visible4 ,and a very wonderful picture they make4 ,we see the transmuting atom flashing out this light for an inconceivably short instant as it throws off the -ray4 ,and so far this little candle throws his beams in the complex system of the cells1 so far atoms shaken by the rays send out -rays2 these in turn are hurled against other atomic systems2 fresh separations of electrons arise and new attractions and repulsions spring up and the most important chemical changes are brought about4 ,our mental picture can claim to be no more than diagrammatic of the reality4 ,still we are here dealing with recognised physical and chemical phenomena1 and their description as occult in the derogatory sense is certainly not justifiable4 ,having now briefly reviewed the nature of the rays arising in radioactive substances and the rationale of their influence1 we must turn to more especially practical considerations4 ,the ,table given opposite shows that radium itself is responsible for a- and -rays only4 ,it happens that #beb ,period in whioh element is transformed4 ,,uranium #a #b a #f x #aji years4 ,,uranium ,x a #bd4f days4 ,,ionium a #h x #ajd years4 ,,radium a #b x #ajb years4 ,,emanation a #h4he days4 ,,radium ,a a #h minutes4 ,,radium ,b y #bf4g minutes4 ,,radium ,c a y #ac4e minutes4 ,,radium ,d #ae years4 ,,radium ,e y #d4h days4 ,,radium 7,polonium7 ,f a #adj days4 ,table showing the successive generations of the elements of the ,uranium-radium family1 the character of their radiations and their longevity4 #bec the -rays emitted by radium are very soft--i4e4 slow and easily absorbed4 ,the a-ray is in no case available for more than mere surface application4 ,hence we see that1 contrary to what is generally believed1 radium itself is of little direct therapeutic value4 ,nor is the next body in succession--the emanation1 for it gives only a-rays4 ,in fact1 to be brief1 it is not till we come to ,radium ,b that -rays of a relatively high penetrative quality are reached2 and it is not till we come to ,radium ,c that highly penetrative y-rays are obtained4 ,it is around this element1 ,radium ,c1 that the chief medical importance of radioactive treatment by this family of radioactive bodies centres4 ,not only are -rays of ,radium ,c very penetrating1 but the y-rays are perhaps the most energetic rays of the1 kind known4 ,further in the list there is no very special medical interest4 ,now1 how can we get a supply of this valuable element ,radium ,c8 ,we can obtain it from radium itself4 ,for even if radium has been deprived of its emanation 7which is easily done by heating it or bringing it into solution7 in a few weeks we get back the ,radium ,c4 ,one thing here we must be clear about4 ,with a given quantity of ,radium only a certain definitely limited amount of ,radium ,c1 or of emanation1 or any other of the derived bodies1 will be associated4 ,why is this8 ,the answer is because the several successive elements are themselves decaying --i4e4 changing one into the other4 ,the atomic per- #bed centage of each1 which decays in a second1 is a fixed quantity which we cannot alter4 ,now if we picture radium which has been completely deprived of its emanation1 again accumulating by automatic transmutation a fresh store of this element1 we have to remember3-- 7i7 ,that the rate of creation of emanation by the radium is practically constant2 and 7#b7 that the absolute amount of the emanation decaying per second increases as the stock of emanation increases4 ,finally1 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 second1 the amount of emanation present cannot increase4 ,this is called the equilibrium amount4 ,if fifteen members are elected steadily each year into a newly-founded society the number of members will increase for the first few years2 finally1 when the losses by death of the members equal about fifteen per annum the society can get no bigger4 ,it has attained the equilibrium number of members4 ,this applies to every one of the successive elements4 ,it takes twenty-one days for the equilibrium quantity of emanation to be formed in radium which has been completely de-emanated2 and it takes #c4h days for half the equilibrium amount to be formed4 ,again1 if we start with a stock of emanation it takes just three hours for the equilibrium amount of ,radium ,c to be formed4 #bee ,we can evidently grow ,radium ,c either from radium itself or from the emanation of radium4 ,if we use a tube of radium we have an almost perfectly constant quantity of ,radium ,c present1 for as fast as the ,radium ,c and intervening elements decay the ,radium1 which only diminishes very slowly in amount1 makes up the loss4 ,but1 if we start off with a tube of emanation1 we do not possess a constant supply of ,radium ,c1 because the emanation is decaying fairly rapidly and there is no radium to make good its loss4 ,in #c4h days about one half the emanation is transmuted and the ,radium ,c decreases proportionately and1 of course1 with the ,radium ,c the valuable radiations also decrease4 ,in another #c4h days--that is in about a week from the start--the radioactive value of the tube has fallen to one-fourth of its original value4 ,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 tube4 ,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 hospital4 ,then1 secondly1 the emanation1 being a gas1 is very convenient for subdivision into a large number of very small tubes according to the dosage required4 ,in fact the volume of the emanation is exceedingly minute4 ,the amount of emanation in equilibrium with one gramme of radium is called the curie1 and with one #bef milligramme the millicurie4 ,now1 the volume of the curie is only a little more than one half a cubic millimetre4 ,hence in dealing with emanation from twenty or forty milligrammes of radium we are dealing with very small volumes4 ,how may the emanation be obtained8 ,the process is an easy one in skilled and practised hands4 ,the salt of radium--generally the bromide or chloride--is brought into acid solution4 ,this causes the emanation to be freely given off as fast as it is formed4 ,at intervals we pump it off with a mercury pump4 ,let us see how many millicuries we will in future be able to turn out in the week in our new ,dublin ,radium ,institute4#a ,we shall have about #acj milligrammes of radium4 ,in #c4h days we get #fe millicuries from this--i4e4 half the equilibrium amount of #acj millicuries4 ,hence in the week1 we shall have about #acj millicuries4 ,this is not much4 ,many experts consider this little enough for one tube4 ,but here in ,dublin we have been using the emanation in a more economical and effective manner than is the usage elsewhere2 according to a method which has been worked out and developed in our own ,radium ,institute4 ,the economy is obtained by the very simple expedient of minutely subdividing the' dose4 ,the system in vogue1 generally1 is to treat the tumour by inserting into it one or two very active #a ,then recently established by the ,royal ,dublin ,society4 #beg tubes1 containing1 perhaps1 up to #bjj millicuries1 or even more1 per tube4 ,now these very heavily charged tubes give a radiation so intense at points close to the tube1 due to the greater density of the rays near the tube1 and1 also1 to the action of the softer and more easily absorbable rays1 that it has been found necessary to stop these softer rays--both the y and --by wrapping lead or platinum round the tube4 ,in this lead or platinum some thirty per cent4 or more of the rays is absorbed and1 of course1 wasted4 ,but in the absence of the screen there is extensive necrosis of the tissues near the tubes4 ,if1 however1 in place of one or two such tubes we use ten or twenty1 each containing one-tenth or one-twentieth of the dose1 we can avail ourselves of the softer rays around each tube with benefit4 ,thus a wasteful loss is avoided4 ,moreover a more uniform illumination of the tissues results1 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 radiation4 ,also we get what is called cross-radiation1which is found to be beneficial4 ,the surgeon knows far better what he is doing by this method4 ,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 locally4 ,finally1 not the least of the benefit arises in the easy technique of this new method4 ,the quantities of #beh emanation employed can fit in the finest capillary glass tubing and the hairlike tubes can in turn be placed in fine exploring needles4 ,there is comparatively little inconvenience to the patient in inserting these needles1 and there is the most perfect control of the dosage in the number and strength of these tubes and the duration of exposure4#a ,the first ,radium ,institute in ,ireland has already done good work for the relief of human suffering4 ,it will have1 ,i hope1 a great future before it1 for ,i venture1 with diffidence1 to hold the opinion1 that with increased study the applications and claims of radioactive treatment will increase4 #a ,for particulars of the new technique and of some of the work already accomplished1 see papers1 by ,dr4 ,walter ,c4 ,stevenson1 ,british ,medical ,journal1 ,july #dth1 #aiad1 and ,march #bjth1 #aiae4 #bei ,,skating #a ,,it is now many years ago since1 as a student1 ,i was present at a college lecture delivered by a certain learned professor on the subject of friction4 ,at this lecture a discussion arose out of a question addressed to our teacher3 ,how is it we can skate on ice and on no other substance8 ,the answer came back without hesitation3 ,because the ice is so smooth4 ,it was at once objected3 ,but you can skate on ice which is not smooth4 ,this put the professor in a difficulty4 ,obviously it is not on account of the smoothness of the ice4 ,a piece of polished plate glass is far smoother than a surface of ice after the latter is cut up by a day's skating4 ,nevertheless1 on the scratched and torn ice-surface skating is still quite possible2 on the smooth plate glass we know we could not skate4 ,some little time after this discussion1 the connection between skating and a somewhat abstruse fact in physical science occurred to me4 ,as the fact itself is one which has played a part in the geological history of the earth1 #a ,a lecture delivered before the ,royal ,dublin ,society in #aije4 #bfj and a part of no little importance1 the subject of skating1 whereby it is perhaps best brought home to every one1 is deserving of our careful attention4 ,let not1 then1 the title of this lecture mislead the reader as to the importance of its subject matter4 ,before going on to the explanation of the wonderful freedom of the skater's movements1 ,i wish to verify what ,i have inferred as to the great difference in the slipperiness of glass and the slipperiness of ice4 ,here is a slab of polished glass4 ,i can raise it to any angle ,i please so that at length this brass weight of #bej grams just slips down when started with a slight shove4 ,the angle is1 as you see1 about #ab degrees4 ,i now transfer the weight on to this large slab of ice which ,i first rapidly dry with soft linen4 ,observe that the weight slips down the surface of ice at a much lower angle4 ,it is a very low angle indeed3 ,i read it as between #d and #e degrees4 ,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 friction4 ,in this experiment1 too1 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 surface4 ,notwithstanding this1 its surface is spotted with small cavities due to bubbles and imperfections4 ,it is certain that if the glass was equally rough1 its angle of friction towards the brass weight would be higher4 #bfa ,we have1 however1 another comparative experiment to carry out4 ,i made as you saw a determination of the angle at which this weight of #bej grams just slipped on the ice4 ,the lower surface of the weight1 the part which presses on the ice1 consists of a light1 brass curtain ring4 ,this can be detached4 ,its mass is only #f grams1 the curtain ring being1 in fact1 hollow and made of very thin metal4 ,we have1 therefore1 in it a very small weight which presents exactly the same surface beneath as did the weight of #bej grams4 ,you see1 now1 that this light weight will not slip on ice at #e or #f degrees of slope1 but first does so at about io degrees4 ,this is a very important experiment as regards our present inquiry4 ,ice appears to possess more than one angle of friction according as a heavy or a light weight is used to press upon it4 ,we will make the same experiment with the plate of glass4 ,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 weight4 ,the light weight requires the same slope of #ab degrees to make it slip4 ,this last result is in accordance with the laws of friction4 ,we say that when solid presses on solid1 for each pair of substances pressed together there is a constant ratio between the force required to keep one in motion over the other1 and the force pressing the solids together4 ,this ratio is calledthe coefficient of friction4,the coefficient is1 in fact1 constant or approximately #bfb so4 ,i can determine the coefficient of friction from the angle of friction by taking the tangent of the angle4 ,the tangent of the angle of friction is the coefficient of friction4 ,if1 then1 the coefficient is constant1 so1 of course1 must the angle of friction be constant4 ,we have seen that it is so in the case of metal on glass1 but not so in the case of metal on ice4 ,this curious result shows that there is something abnormal about the slipperiness of ice4 ,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 it4 ,i have here a means of dealing with a surface of cold1 dry ice4 ,this shallow copper tank about #ah inches 7#de cms47 long1 and #d inches 7#aj cms47 wide1 is filled with a freezing 'mixture circulated through it from a larger vessel containing ice melting in hydrochloric acid at a temperature of about -#ah ,c4 ,this keeps the tank below the melting point of ice4 ,the upper surface of the tank is provided with raised edges so that it can be flooded with water4 ,the water is now frozen and its temperature is below #j ,c4 ,it is about #aj ,c4 ,i can place over the ice a roof-shaped cover made of two inclined slabs of thick plate glass4 ,this acts to keep out warm air1 and to do away with any possibility of the surface of the ice being wet with water thawed from the ice4 ,the whole tank along with its roof of glass can be adjusted to any angle1 and a1 scale at the #bfc raised end of the tank gives the angle of slope in degrees4 ,a weight placed on the ice can be easily seen through the glass cover4 ,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 it4 ,the weight rests now on a copper plate provided for the purpose at the upper end of the tank4 ,the plate being in direct contact beneath with the freezing mixture we are sure that the aluminium ring is no hotter than the ice4 ,a light jerk suffices to shake the weight on to the surface of the ice4 ,we find that this ring loaded with only the ping-pong ball1 and weighing a total of #b4ee grams does not slip at the low angles4 ,i have the surface of the ice at an angle of rather over #ac1 and only by continuous tapping of the apparatus can it be induced to slip down4 ,this is a coefficient of #j4bd1 and compares with the coefficient of hard and smooth solids on one another4 ,i now replace the empty ping-pong ball by a similar ball filled with lead shot4 ,the total weight is now #aee grams4 ,you see the angle of slipping has fallen to #g4 ,every one who has made friction experiments knows how unsatisfactory and inconsistent they often are4 ,we can only discuss notable quantities and broad results1 unless the most conscientious care be taken to eliminate errors4 ,the net result here is that ice at about -#aj ,c4 when pressed on by a very light weight possesses a #bfd coefficient of friction comparable with the usual coefficients of solids on solids1 but when the pressure is increased1 the coefficient falls to about half this value4 ,the following table embodies some results obtained on the friction of ice and glass1 using the methods ,i have shown you4 ,i add some of the more carefully determined coefficients of other observers4 ,wt4 in ,on ,plate ,on ,ice ,on ,ice ,grams4 ,glass4 at #j ,c4 at #aj ,c4 ,angle4 ,coeff4 ,angle4 ,coeff4 ,angle4 ,coeff ,aluminium #b4ee #ab #j4bb #ab #j4ba #ac #j4bd ,same #aee #ab #j4bb #f #j4aa #g #j4ab ,brass #f4e #ab #j4bb #aj #j4ag #aj #j4ah ,same #ajg #ab #j4bb #e #j4ji #f #j4aj ,steel on steel 7,morin7 - - - - #j4ad ,brass on cast iron 7,morin7 - - #j4ai ,steel on cast iron 7,morin7 - - #j4bj ,skate on ice 7,j4 ,mller7 - - - #j4jaf--j4jcb ,best-greased surfaces 7,perry7 - #j4jc--j4jcf ,you perceive from the table that while the friction of brass or aluminium on glass is quite independent of the weight used1 that of brass or aluminium on ice depends in some way upon the weight1 and falls in a very marked degree when the weight is heavy4 ,now1 ,i think that if we had been on the look out for any abnormality in the friction of hard substances on ice1 we would have rather anticipated a variation in the #bfe other direction4 ,we would have1 perhaps1 expected that a heavy weight would have given rise to the greater friction4 ,i now turn to the explanation of this extraordinary result4 ,you are aware that it requires an expenditure of heat merely to convert ice to water1 the water produced being at the temperature of the ice1 i4e4 at #j ,c41 from which it is derived4 ,the heat required to change the ice from the solid to the liquid state is the latent heat of water4 ,we take the unit quantity of heat to be that which is required to heat #a kilogram of water #a ,c4 ,then if we melt #a kilogram of ice1 we must supply it with #hj such units of heat4 ,while melting is going on1 there is no change of temperature if the experiment is carefully conducted4 ,the melting ice and the water coming from it remain at #j ,c4 throughout the operation1 and neither the thermometer nor your own sensations would tell you of the amount of heat which was flowing in4 ,the heat is latent or hidden in the liquid produced1 and has gone to do molecular work in the substance4 ,observe that if we supply only #dj thermal units1 we get only one-half the ice melted4 ,if only #aj units are supplied1 then we get only one eighth of a kilogram of water1 and no more nor less4 ,i have ventured to recall to you these commonplaces of science before considering a mode of melting ice which is less generally known1 and which involves no supply of heat on your part4 ,this method involves for its #bff understanding a careful consideration of the thermal properties of water in the solid state4 ,it must have been observed a very long time ago that water expands when it freezes4 ,otherwise ice would not float on water2 and1 what is perhaps more important in your eyes1 your water pipes would not burst in winter when the water freezes therein4 ,but although the important fact of the expansion of water on freezing was so long presented to the observation of mankind1 it was not till almost exactly the middle of the last century that ,james ,thomson1 a gifted ,irishman1 predicted many important consequences arising from the fact of the expansion of water on becoming solid4 ,the principles lie enunciated are perfectly general1 and apply in every case of change of volume attending change of state4 ,we are here only concerned with the case of water and ice4 ,james ,thomson1 following a train of thought which we cannot here pursue1 predicted that owing to the fact of the expansion of water on becoming solid1 pressure will lower the melting point of ice or the freezing point of water4 ,normally1 as you are aware1 the temperature is #j ,c4 or #cb ,f4 ,thomson said that this would be found to be the freezing point only at atmospheric pressure4 ,he calculated how much it would change with change of pressure4 ,he predicted that the freezing point would fall #j4jjge of a degree ,centigrade for each additional atmosphere of pressure applied to the water4 ,suppose1 #bfg for instance1 our earth possessed an atmosphere so heavy to as exert a thousand times the pressure of the existing atmosphere1 then water would not freeze at #j ,c41 but at -#g4e ,c4 or about #ah ,f4 ,again1 in vacuo1 that is when the pressure has been reduced to the relatively small vapour pressure of the water1 the freezing point is above #j ,c41 i4e4 at #j4jjge ,c4 ,in parts of the ocean depths the pressure is much over a thousand atmospheres4 ,fresh water would remain liquid there at temperatures much below #j ,c4 ,it will be evident enough1 even to those not possessed of the scientific insight of ,james ,thomson1 that some such fact is to be anticipated4 ,it is1 however1 easy to be wise after the event4 ,it appeals to us in a general way that as water expands on freezing1 pressure will tend to resist the turning of it to ice4 ,the water will try to remain liquid in obedience to the pressure4 ,it will1 therefore1 require a lower temperature to induce it to become ice4 ,james ,thomson left his thesis as a prediction4 ,but he predicted exactly what his distinguished brother1 ,sir ,william ,thomson--later ,lord ,kelvin--found to happen when the matter was put to the test of experiment4 ,we must consider the experiment made by ,lord ,kelvin4 ,according to ,thomson's views1 if a quantity of ice and water are compressed1 there must be a fall of temperature4 ,the nature of his argument is as follows3 #bfh ,let the ice and water be exactly at #j ,c4 to start with4 ,then suppose we apply1 say1 one thousand atmospheres pressure4 ,the melting point of the ice is lowered to -#g4e ,c4 ,that is1 it will require a temperature so low as -#g4e ,c4 to keep it solid4 ,it will therefore at once set about melting1 for as we have seen1 its actual temperature is not -#g4e ,c41 but a higher temperature1 i4e4 #j ,c4 ,in other words1 it is #g4e above its melting point4 ,but as soon as it begins melting it also begins to absorb heat to supply the #hj thermal units which1 as we know1 are required to turn each kilogram of the ice to water4 ,where can it get this heat8 ,we assume that we give it none4 ,it has only two sources1 the ice can take heat from itself1 and it can take heat from the water4 ,it does both in this case1 and both ice and water drop in temperature4 ,they fall in temperature till -#g4e is reached4 ,then the ice has got to its melting point under the pressure of one thousand atmospheres1 or1 as we may put it1 the water has reached its freezing point4 ,there can be no more melting4 ,the whole mass is down to -#g4e ,c41 and will stay there if we keep heat from flowing either into or out of the vessel4 ,there is now more water and less ice in the vessel than when we started1 and the temperature has fallen to -#g4e ,c4 ,the fall of temperature to the amount predicted by the theory was verified by ,lord ,kelvin4 ,suppose we now suddenly remove the pressure2 what will happen8 ,we have water and ice at -#g4e ,c4 #bfi and at the normal pressure4 ,water at -#g4e and at the normal pressure of course turns to ice4 ,the water will1 therefore1 instantly freeze in the vessel1 and the whole process will be reversed4 ,in freezing1 the water will give up its latent heat1 and this will warm up the whole mass till once again #j ,c4 is attained4 ,then there will be no more freezing1 for again the ice is at its melting point4 ,this is the remarkable series of events which ,james ,thomson predicted4 ,and these are the events which ,lord ,kelvin by a delicate series of experiments1 verified in every respect4 ,suppose we had nothing but solid ice in the vessel at starting1 would the experiment result in the same way8 ,yes1 it assuredly would4 ,the ice under the increased pressure would melt a little everywhere throughout its mass1 taking the requisite latent heat from itself at the expense of its sensible heat1 and the temperature of the ice would fall to the new melting point4 ,could we melt the whole of the ice in this manner8 ,again the answer is yes4 ,but the pressure must be very great4 ,if we assume that all the heat is obtained at the expense of the sensible heat of the ice1 the cooling must be such as to supply the latent heat of the whole mass of water produced4 ,however1 the latent heat diminishes as the melting point is lowered1 and at a rate which would reduce it to nothing at about #ah1jjj atmospheres4 ,mousson1 operating on ice enclosed in a conducting cylinder and cooled to -#ah at starting #bgj appears to have obtained very complete liquefaction4 ,mousson must have attained a pressure of at least an amount adequate to lower the melting point below -#ah4 ,the degree of liquefaction actually attained may have been due in part to the passage of heat through the walls of the vessel4 ,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 on4 ,i have here a simple way of demonstrating to you the fall of temperature attending the compression of ice4 ,in this mould1 which is strongly made of steel1 lined with boxwood to diminish the passage of conducted heat1 is a quantity of ice which ,i compress when ,i force in this plunger4 ,in the ice is a thermoelectric junction1 the wires leading to which are in communication with a reflecting galvanometer4 ,the thermocouple is of copper and nickel1 and is of such sensitiveness as to show by motion of the spot of light on the screen even a small fraction of a degree4 ,on applying the pressure1 you see the spot of light is displaced1 and in such a direction as to indicate cooling4 ,the balancing thermocouple is all the time imbedded in a block of ice so that its temperature remains unaltered4 ,on taking off the pressure1 the spot of light returns to its first position4 ,i can move the spot of light backwards and forwards on the screen by taking off and putting on the pressure4 ,the effects are quite instantaneous4 #bga ,the fact last referred to is very important4 ,the ice1 in fact1 is as it were automatically turned to water4 ,it is not a matter of the conduction of heat from point to point in the ice4 ,its own sensible heat is immediately absorbed throughout the mass4 ,this would be the theoretical result1 but it is probable that owing to imperfections throughout the ice and failure in uniformity in the distribution of the stress1 the melting would not take place quite uniformly or homogeneously4 ,before applying our new ideas to skating1 ,i want you to notice a fact which ,i have inferentially stated1 but not specifically mentioned4 ,pressure will only lead to the melting of ice if the new melting point1 i4e4 that due to the pressure1 is below the prevailing temperature4 ,let us take figures4 ,the ice to start with is1 say1 at -#c ,c4 ,suppose we apply such a pressure to this ice as will confer a melting point of -#b ,c4 on it4 ,obviously1 there will be no melting4 ,for why should ice which is at -#c ,c4 melt when its melting point is -#b ,c48 ,the ice is1 in fact1 colder than its melting point4 ,hence1 you note this fact3 ,the pressure must be sufficiently intense to bring the melting point below the prevailing temperature1 or there will be no melting2 and the further we reduce the melting point by pressure below the prevailing temperature1 the more ice will be melted4 ,we come at length to the object of our remarks ,i don't know who invented skating or skates4 ,it is said that in the thirteenth century the inhabitants of #bgb ,england used to amuse themselves by fastening the bones of an animal beneath their feet1 and pushing themselves about on the ice by means of a stick pointed with iron4 ,with such skates1 any performance either on inside or outside edge was impossible4 ,we are a conservative people4 ,this exhilarating amusement appears to have served the people of ,england for three centuries4 ,not till #affj were wooden skates shod with iron introduced from the ,netherlands4 ,it is certain that skating was a fashionable amusement in ,pepys' time4 ,he writes in #affb to the effect3 ,it being a great frost1 did see people sliding with their skates1 which is a very pretty art4 ,it is remarkable that it was the ,german poet ,klopstock who made skating fashionable in ,germany4 ,until his time1 the art was considered a pastime1 only fit for very young or silly people4 ,i wish now to dwell upon that beautiful contrivance the modern skate4 ,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 development4 ,for what are the principles underlying the proper construction of the skate8 ,after what ,i have said1 ,i think you will readily understand4 ,the object is to produce such a pressure under the blade that the ice will melt4 ,we wish to establish such a pressure under the skate that even on a day when the ice is below zero1 its melting #bgc point is so reduced just under the edge of the skate that the ice turns to water4 ,it is this melting of the ice under the skate which secures the condition essential to skating4 ,in the first place1 the skate no longer rests on a solid4 ,it rests on a liquid4 ,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 liquid4 ,look at the bearings of a steam engine4 ,a continuous stream of oil is fed in to interpose itself between the solid surfaces4 ,i need not illustrate so well-known a principle by experiment4 ,solid friction disappears when the liquid intervenes4 ,in its place we substitute the lesser difficulty of shearing one layer of the liquid over the other2 and if we keep up the supply of oil the work required to do this is not very different1 no matter how great we make the pressure upon the bearings4 ,compared with the resistance of solid friction1 the resistance of fluid friction is trifling4 ,here under the skate the lubrication is perhaps the most perfect which it is possible to conceive4 ,j4 ,mller has determined the coefficient by towing a skater holding on by a spring balance4 ,the coefficient is between #j4jaf and #j4jcb4 ,in other words1 the skater would run down an incline so little as #a or #b degrees2 an inclination not perceivable by the eye4 ,now observe that the larger of these coefficients is almost exactly the same as that which ,perry found in the case of well-greased surfaces4 ,but evidently no #bgd artificial system of lubrication could hope to equal that which exists between the skate and the ice4 ,for the lubrication here is1 as it were1 automatic4 ,in the machine if the lubricant gets squeezed out there instantly ensues solid friction4 ,under the skate this cannot happen for the squeezing out of the lubricant is instantly followed by the formation of another film of water4 ,the conditions of pressure which may lead to solid friction in the machine here automatically call the lubricant into existence4 ,just under the edge of the skate the pressure is enormous4 ,consider that the whole weight of the skater is born upon a mere knife edge4 ,the skater alternately throws his whole weight upon the edge of each skate4 ,but not only is the weight thus concentrated upon one edge1 further concentration is secured in the best skates by making the skate hollow-ground1 i4e4 increasing the keenness of the edge by making it less than a right angle4 ,still greater pressure is obtained by diminishing the length of that part of the blade which is in contact with the ice4 ,this is done by putting curvature on the blade or making it what is called hog-backed4 ,you see that everything is done to diminish the area in contact with the ice1 and thus to increase the pressure4 ,the result is a very great compression of the ice beneath the edge of the skate4 ,even in the very coldest weather melting must take place to some extent4 ,as we observed before1 the melting is instantaneous1 #bge ,heat has not to travel from one point of the ice to another2 immediately the pressure comes on the ice it turns to water4 ,it takes the requisite heat from itself in order that the change of state may be accomplished4 ,so soon as the skate passes on1 the water resumes the solid state4 ,it is probable that there is an instantaneous escape1 and re-freezing of some of the water from beneath the skate1 the skate instantly taking a fresh bearing and melting more ice4 ,the temperature of the water escaping from beneath the skate1 or left behind by it1 immediately becomes what it was before the skate pressed upon it4 ,thus1 a most wonderful and complex series of molecular events takes place beneath the skate4 ,swift as it passes1 the whole sequence of events which ,james ,thomson predicted has to take place beneath the blade ,compression2 lowering of the melting point below the temperature of the surrounding ice2 melting2 absorption of heat2 and cooling to the new melting point1 i4e4 to that proper to the pressure beneath the blade4 ,the skate now passes on4 ,then follow3 ,relief of pressure2 re-solidification of the water2 restoration of the borrowed heat from the congealing water and reversion of the ice to the original temperature4 ,if we reflect for a moment on all this1 we see that we do not skate on ice but on water4 ,we could not skate on ice any more than we could skate on glass4 ,we saw that with light weights and when the pressure #bgf ,diagram ,diagram showing successive states obtaining in ice1 before1 during1 and after the passage of the skate4 ,the temperatures and pressures selected for illustration are such as might occur under ordinary conditions4 ,the edge of the skate is shown in magnified cross-section4 #bgg ,was not sufficient to melt the ice1 the friction was much the same as that of metal on glass4 ,ice is not slippery4 ,it is an error to say that it is4 ,the learned professor was very much astray when he said that you could skate on ice because it is so smooth4 ,the smoothness of the ice has nothing to do with the matter4 ,in short1 owing to the action of gravity upon your body1 you escape the normal resistance of solid on solid1 and glide about with feet winged like the messenger of the ,gods2 but on water4 ,a second condition essential to the art of skating is also involved in the melting of the ice4 ,the sinking of the skate gives the skater bite4 ,this it is which enables him to urge himself forward4 ,so long as skates consisted of the rounded bones of animals1 the skater had to use a pointed staff to propel himself4 ,in creating bite1 the skater again unconsciously appeals to the peculiar physical properties of ice4 ,the pressure required for the propulsion of the skater is spread all along the length of the groove he has cut in the ice1 and obliquely downwards4 ,the skate will not slip away laterally1 for the horizontal component of the pressure is not enough to melt the ice4 ,he thus gets the resistance he requires4 ,you see what a very perfect contrivance the skate is2 and what a similitude of intelligence there is in its evolution4 ,blind intelligence1 because it is certain the true physics of skating was never held in view by #bgh the makers of skates4 ,the evolution of the skate has been truly organic4 ,the skater selected the fittest skate1 and hence the fit skate survived4 ,in a word1 the possibility of skating depends on the dynamical melting of ice under pressure4 ,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 it4 ,if ice was less bulky than the water from which it was derived1 pressure would not melt it2 it would be all the more solid for the pressure1 as it were4 ,the melting point would rise instead of falling4 ,most substances behave in this manner1 and hence we cannot skate upon them4 ,only quite a few substances expand on freezing1 and it happens that their particular melting temperatures or other properties render them unsuitable to skating4 ,the most abundant fluid substance on the earth1 and the most abundant substance of any one kind on its surface1 thus possesses the ideally correct and suitable properties for the art of skating4 ,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 time4 ,we have seen also1 that one atmosphere lowers the melting point of ice by the #a_/adj of a degree ,centigrade2 more exactly by #j4jjge4 ,let us now assume that the skate is so far sunken in the ice as to bear for a length of two inches1 and for a width of one-hundredth of an inch4 ,the skater weighs1 #bgi let us say--#aej pounds4 ,if this weight was borne on one square inch1 the pressure would be ten atmospheres4 ,but the skater rests his weight1 in fact1 upon an area of one-fiftieth of an inch4 ,the pressure is1 therefore1 fifty times as great4 ,the ice is subjected to a pressure of #ejj atmospheres4 ,this lowers the melting point to -#c4ge ,c4 ,hence1 on a day when the ice is at this temperature1 the skate will sink in the ice till the weight of the skater is concentrated as we have assumed4 ,his skate can sink no further1 for any lesser concentration of the pressure will not bring the melting point below the prevailing temperature4 ,we can calculate the theoretical bite for any state of the ice4 ,if the ice is colder the bite will not be so deep4 ,if the temperature was twice as far below zero1 then the area over which the skater's weight will be distributed1 when the skate has penetrated its maximum depth1 will be only half the former area1 and the pressure will be one thousand atmospheres4 ,an important consideration arises from the fact that under the very extreme edge of the skate the pressure is indefinitely great4 ,for this involves that there will always be some bite1 however cold the ice may be4 ,that is1 the narrow strip of ice which first receives the skater's weight must partially liquefy however cold the ice4 ,it must have happened to many here to be on ice which was too cold to skate on with comfort4 ,the #bhj skater in this case speaks of the ice as too hard4 ,in the ,engadine1 the ice on the large lakes gets so cold that skaters complain of this4 ,on the rinks1 which are chiefly used there1 the ice is frequently renewed by flooding with water at the close of the day4 ,it thus never gets so very cold as on the lakes4 ,i have been on ice in ,north ,france1 which1 in the early morning1 was too hard to afford sufficient bite for comfort4 ,the cause of this is easily understood from what we have been considering4 ,we may now return to the experimental results which we obtained early in the lecture4 ,the heavy weights slip off the ice at a low angle because just at the points of contact with the ice the latter melts1 and they1 in fact1 slip not on ice but on water4 ,the light weights on cold1 dry ice do not lower the melting point below the temperature of the ice1 i4e4 below -#aj ,c41 and so they slip on dry ice4 ,they therefore give us the true coefficient of friction of metal on ice4 ,this subject has1 more recently been investigated by ,h4 ,morphy1 of ,trinity ,college1 ,dublin4 ,the refinement of a closed vessel at uniform temperature1 in which the ice is formed and the experiment carried out1 is introduced4 ,thermocouples give the temperatures1 not only of the ice but of the aluminium sleigh which slips upon it under various loads4 ,in this way we may be certain that the metal runners are truly at the temperature of the ice4 ,i now quote from ,morphy's paper #bha ,the angle of friction was found to remain constant until a certain stage of the loading1 when it suddenly fell to about half of its original value4 ,it then remained constant for further increases in the load4 ,these results1 which confirmed those obtained previously with less satisfactory apparatus1 are shown in the table below4 ,in the first column is shown the load1 i4e4 the weight of sleigh weight of shot added4 ,in the second and third columns are shown1 respectively1 the coefficient and angle of friction1 whilst the fourth gives the temperature of the ice as determined from the galvanometer deflexions4 ,load4 ,tan y4 y4 ,temp4 #e4fh grams4 #j4cf4ja #bjcj' -#e4fe ,c4 #aj4ci -#e4fe #aa4if -#e4ge #ab4gd -#e4fj #ac4ec -#e4fe #ad4ca -#e4fe #ae4aj grams4 #j4ag4ja #i4cj'cj' -#e4fj #af4fg -#e4ee #ai4ha -#e4fj #bd4eb -#e4fj #e4fh grams4 #j4cf4ja #bjcj' -#e4fj ,these experiments were repeated on another occasion with the same result and similar results had been obtained with different apparatus4 ,as a result of the investigation the following points are clearly shown3-- #bhb 7#a7 ,the coefficient of friction for ice at constant temperature may have either of two constant values according to the pressure per unit surface of contact4 7#b7 ,for small pressures1 and up to a certain well defined limit of pressure1 the coefficient is fairly large1 having the value #j4cf4ja in the case investigated4 7#c7 ,for pressures greater than the above limit the coefficient is relatively small1 having the value #j4ag4ja in the case investigated4 ,it will be seen that ,morphy's results are similar to those arrived at in the first experimental consideration of our subject2 but from the manner in which the experiments have been carried out1 they are more accurate and reliable4 ,a great deal more might be said about skating1 and the allied sports of tobogganing1 sleighing1 curling1 ice yachting1 and last1 but by no means least1 sliding--that unpretentious pastime of the million4 ,happy the boy who has nails in his boots when ,jack-,frost appears in his white garment1 and congeals the neighbouring pond4 ,but ,i must turn away at the threshold of the humorous aspect of my subject 7for the victim of the street slide owes his injured dignity to the abstruse laws we have been discussing7 and pass to other and graver subjects intimately connected with skating4 ,james ,thomson pointed out that if we apply compressional stress to an ice crystal contained in a vessel #bhc which also contains other ice crystals1 and water at #j ,c41 then the stressed crystal will melt and become water1 but its counterpart or equivalent quantity of ice will reappear elsewhere in the vessel4 ,this is1 obviously1 but a deduction from the principles we have been examining4 ,the phenomenon is commonly called regelation4 ,i have already made the usual regelation experiment before you when ,i compressed broken ice in this mould4 ,the result was a clear1 hard and almost flawless lens of ice4 ,now in this operation we must figure to ourselves the pieces of ice when pressed against one another melting away where compressed1 and the water produced escaping into the spaces between the fragments1 and there solidifying in virtue of its temperature being below the freezing point of unstressed water4 ,the final result is the uniform lens of ice4 ,the same process goes on in a less perfect manner when you make--or shall ,i better say--when you made snowballs4 ,we now come to theories of glacier motion2 of which there are two4 ,the one refers it mainly to regelation2 the other to a real viscosity of the ice4 ,the late ,j4 ,c4 ,m',connel established the fact that ice possesses viscosity2 that is1 it will slowly yield and change its shape under long continued stresses4 ,his observations1 indeed1 raise a difficulty in applying this viscosity to explain glacier motion1 for he showed that an ice crystal is only viscous in a certain structural #bhd direction4 ,a complex mixture of crystals such1 as we know glacier ice to be1 ought1 we would imagine1 to display a nett or resultant rigidity4 ,a mass of glacier ice when distorted by application of a force must1 however1 undergo precisely the transformations which took place in forming the lens from the fragments of ice4 ,in fact1 regelation will confer upon it all the appearance of viscosity4 ,let us picture to ourselves a glacier pressing its enormous mass down a ,swiss valley4 ,at any point suppose it to be hindered in its downward path by a rocky obstacle4 ,at that point the ice turns to water just as it does beneath the skate4 ,the cold water escapes and solidifies elsewhere4 ,but note this1 only where there is freedom from pressure4 ,in escaping1 it carries away its latent heat of liquefaction1 and this we must assume1 is lost to the region of ice lately under pressure4 ,this region will1 however1 again warm up by conduction of heat from the surrounding ice1 or by the circulation of water from the suxface4 ,meanwhile1 the pressure at that point has been relieved4 ,the mechanical resistance is transferred elsewhere4 ,at this new point there is again melting and relief of pressure4 ,in this manner the glacier may be supposed to move down4 ,there is continual flux of conducted heat and converted latent heat1 hither and thither1 to and from the points of resistance4 ,the final motion of the whole mass is necessarily slow2 a few feet in the day or1 in winter1 #bhe even only a few inches4 ,and as we might expect1 perfect silence attends the downward slipping of the gigantic mass4 ,the motion is1 ,i believe1 sufficiently explained as a skating motion4 ,the skate is1 however1 fixed1 the ice moves4 ,the great ,aletsch ,glacier collects its snows among the highest summits of the ,oberland4 ,thence1 the consolidated ice makes its way into the ,rhone ,valley1 travelling a distance of some #bj miles4 ,the ice now melting into the youthful ,rhone fell upon the ,monch1 the ,jungfrau or the ,eiger in the days when ,elizabeth ruled in ,england and ,shakespeare lived4 ,the ice-fall is a common sight on the glacier4 ,in great lumps and broken pinnacles it topples over some rocky obstacle and falls shattered on to the glacier below4 ,but a little further down the wound is healed again1 and regelation has restored the smooth surface of the glacier4 ,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 state4 ,we thus have arrived at very far-reaching considerations arising out of skating and its science4 ,the tendency for snow to accumulate on the highest regions of the ,earth depends on principles which we cannot stop to consider4 ,we know it collects above a certain level even at the ,equator4 ,we may consider1 then1 that but for the operation of the laws which ,james ,thomson brought to light1 and which his illustrious brother1 #bhf ,lord ,kelvin1 made manifest1 the uplands of the ,earth could not have freed themselves of the burthen of ice4 ,the geological history of the ,earth must have been profoundly modified4 ,the higher levels must have been depressed2 the general level of the ocean relatively to the land thereby raised1 and1 it is even possible1 that such a mean level might have been attained as would result in general submergence4 ,during the last great glacial period1 we may say the fate of the world hung on the operation of those laws which have concerned us throughout this lecture4 ,it is believed the ice was piled up to a height of some #f1jjj feet over the region of ,scandinavia4 ,under the influence of the pressure and fusion at points of resistance1 the accumulation was stayed1 and it flowed southwards the accumulation was stayed1 and it flowed southwards over ,northern ,europe4 ,the ,highlands of ,scotland were covered with1 perhaps1 three or four thousand feet of ice4 ,ireland was covered from north to south1 and mighty ice-bergs floated from our western and southern shores4 ,the transported or erratic stones1 often of great size1 which are found in many parts of ,ireland1 are records of these long past events3 events which happened before ,man1 as a rational being1 appeared upon the ,earth4 #bhg ,a ,,speculation ,,as ,,to ,a ,,prematerial ,,universe #a ,and therefore444these things likewise had a birth2 for things which are of mortal body could not for an infinite time back444 have been able to set at naught the puissant strength of immeasurable age4--,,lucretius1 ,de ,rerum ,natura4 ,o fearful meditation6 ,where1 alack6 ,shall ,time's best jewel from ,time's chest lie hid8 --,,shakespeare4 ,,in the material universe we find presented to our senses a physical development continually progressing1 extending to all1 even the most minute1 material configurations4 ,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 volume4#b ,in the present essay1 these systems as having a common origin and common ending1 are merged in the same consideration as to the nature of the origin of material systems in general4 ,this present essay is occupied by the consideration of the necessity of limiting material interactions in past time4 ,the speculation originated in the difficulties which present themselves when we ascribe to these interactions infinite duration in the past4 ,these difficulties first claim our consideration4 #a ,proc4 ,royal ,dublin ,soc41 vol4 vii41 ,part ,v1 #ahib4 #b ,the ,abundance of ,life4 #bhh ,accepting the hypothesis of ,kant and ,laplace in its widest extension1 we are referred to a primitive condition of wide material diffusion1 and necessarily too of material instability4 ,the hypothesis is1 in fact1 based upon this material instability4 ,we may pursue the sequence of events assumed in this hypothesis into the future1 and into the past4 ,in the future we find finality to progress clearly indicated4 ,the hypothesis points to a time when there will be no more progressive change but a mere sequence of unfruitful events1 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 parts4 ,or1 again1 if the ether absorb the energy of material motion1 this vast and dark aggregation eternally poised and at rest within it4 ,the action is transferred to the subtle parts of the ether which suffer none of the energy to degrade4 ,this is1 physically1 a thinkable future4 ,our minds suggest no change1 and demand none4 ,more than this1 change is unthinkable according to our present ideas of energy4 ,of progress there is an end4 ,this finality parte post is instructive4 ,abstract considerations1 based on geometrical or analytical illustrations1 question the finiteness of some physical developments4 ,thus our sun may require eternal time to attain the temperature of the ether around it1 the approach to this condition being assumed to be asymptotic in #bhi character4 ,but consider the legitimate reductio ad absurdum of an ember raked from a fire #ajjj years ago4 ,is it not yet cooled down to the constant temperature of its surroundings8 ,and we may evidently increase the time a million-fold if we please4 ,it appears as if we must regard eternity as outliving every progressive change1 ,for there is no convergence or enfeeblement of time4 ,the ever-flowing present moves no differently for the occurrence of the mightiest or the most insignificant events4 ,and even if we say that time is only the attendant upon events1 yet this attendant waits patiently for the end1 however long deferred4 ,does the essentially material hypothesis of ,kant and ,laplace account for an infinite past as thinkably as it accounts for the infinite future8 ,as this hypothesis is based upon material instability the question resolves itself into this3-- ,is the assumption of an infinitely prolonged past instability a probable or possible account of the past8 ,there are1 it appears to me1 great difficulties involved in accepting the hypothesis of infinitely prolonged material instability4 ,i will refer here to three principal objections4 ,the first may be called a metaphysical objection2 the second is partly metaphysical and partly physical1 the third may be considered a physical objection1 as it is involved directly in the phenomena presented by our universe4 ,the metaphysical objection must have presented itself to every one who has considered the question4 ,it may #bij be put thus3--,if present events are merely one stage in an infinite progress1 why is not the present stage long ago passed over8 ,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 this1 and so on1 for1 by hypothesis1 there is no beginning to the progress4 ,thus1 the sum of passing events constituting the present universe should long ago have been accomplished and passed away4 ,if we consider alternative hypotheses not involving this difficulty1 we are at once struck by the fact that the future of material development is free of the objection4 ,for the eternity of unprogressive events involved in the future on ,kant's hypothesis1 is not only thinkable1 but any change is1 as observed1 irreconcilable with our ideas of energy4 ,as in the future so in the past we look to a cessation to progress4 ,but as we believe the activity of the present universe must in some form have existed all along1 the only refuge in the past is to imagine an active but unprogressive eternity1 the unprogressive activity at some period becoming a progressive activity--that progressive activity of which we are spectators4 ,to the unprogressive activity there was no beginning2 in fact1 beginning is as unthinkable and uncalled for to the unprogressive activity of the past as ending is to the unprogressive activity of the future1 when all developmental actions shall have ceased4 ,there is no beginning or ending to the activity of the universe4 #bia ,there is beginning and ending to present progressive activity4 ,looking through the realm of nature we seek beginning and ending1 but passing through nature to eternity we find neither4 ,both are justified2 the questioning of the ancient poet regarding the past1 and of the modern regarding the future1 quoted at the head of this essay4 ,the next objection1 which is in part metaphysical1 is founded on the difficulty of ascribing any ultimate reality or potency to forces diminishing through eternal time4 ,thus1 against the assumption that our universe is the result of material aggregation progressing over eternal time1 which involves the primitive infinite separation of the particles1 we may ask1 what force can have acted between particles sundered by infinite distance8 ,the gravitational force falling off as the square of the distance1 must vanish at infinity if we mean what we say when we ascribe infinite separation to them4 ,their condition is then one of neutral stability1 a finite movement of the particles neither increasing nor diminishing interaction4 ,they had then remained eternally in their separated condition1 there being no cause to render such condition finite4 ,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 elapsed4 ,in both cases we are bound to prolong the time1 from our very idea of time1 till progress is no more1 when in the one case we can imagine no mutual approximation of the #bib particles1 in the other no further cooling of the body4 ,however1 ,i will riot dwell further upon this objection1 as it does not1 ,i believe1 present itself with equal force to every mind4 ,a reason less open to dispute1 as being less subjective1 against the aggregation of infinitely remote particles as the origin of our universe1 is contained in the physical objection4 ,in this objection we consider that the appearance presented by our universe negatives the hypothesis of infinitely prolonged aggregation4 ,we base this negation upon the appearance of simultaneity presented by the heavens1 contending that this simultaneity is contrary to what we would expect to find in the case of particles gathered from infinitely remote distances4 ,whether these particles were endowed with relative motions or not is unimportant to the consideration4 ,in what respects do the phenomena of our universe present the appearance of simultaneous phenomena8 ,we must remember that the suns in space are as fires which brighten only for a moment and are then extinguished4 ,it is in this sense we must regard the longest burning of the stars4 ,whether just lit or just expiring counts little in eternity4 ,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 insect4 ,sir ,william ,herschel says of the galaxy of the milky way3-- ,we do not know the rate of progress of this mysterious chronometer1 but it is nevertheless certain that it cannot #bic last for ever1 and its past duration cannot be infinite4 ,we do not know1 indeed1 the rate of progress of the chronometer1 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 wheel4 ,hence we must regard the hosts of glittering stars as a conflagration that has been simultaneously lighted up in the heavens4 ,the enormous 7to our ideas7 thermal energy of the stars resembles the scintillation of iron dust in a jar of oxygen when a pinch of the dust is thrown in4 ,although some particles be burnt up before others become alight1 and some linger yet a little longer than the others1 in our day's work the scintillation of the iron dust is the work of a single instant1 and so in the long night of eternity the scintillation of the mightiest suns of space is over in a moment4 ,a little longer1 indeed1 in duration than the life which stirs a moment in response to the diffusion of the energy1 but only very little4 ,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 thought4 ,the latter indeed are no more lasting than 444 the labour of ants ,in the light of a million million of suns4 ,but the myriad suns themselves1 with their generations1 are the momentary gleam of lights for ever after extinguished4 #bid ,again1 science suggests that the present process of material aggregation is not finished1 and possibly will only be when it prevails universally4 ,hence the very distribution of the stars1 as we observe them1 as isolated aggregations1 indicates a development which in the infinite duration must be regarded as equally advanced in all parts of stellar space and essentially a simultaneous phenomenon4 ,for were we spectators of a system in which any very great difference of age prevailed1 this very great difference would be attended by some such appearance as the following3-- ,the aupearance of but one star1 other generations being long extinct or no others yet come into being2 or1 perhaps1 a faint nebulous wreath of aggregating matter somewhere solitary in the heavens2 or no sign of matter beyond our system1 either because ungathered or long passed away into darkness4#a ,some such appearances were to be expected had the aggregation of matter depended solely on chance encounters of particles scattered through infinite space4 ,for as1 by hypothesis1 the aggregation occupies an infinite time in consummation it is nearly a certainty that each particle encountered after immeasurable time1 and then for the first time endowed with actual gravitational potential energy1 would have long expended this energy #a ,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 life4 #bie before another particle was gathered4 ,but the fact that so many fires which we know to be of brief duration are scattered through a region of space1 and the fact of a configuration which we believe to be a transitory ore1 suggest their simultaneous aggregation here and there4 ,and in the nebulous wreaths situated amidst the stars there is evidence that these actually originated where they now are1 for in such no relative motion1 ,i believe1 has as yet been detected by the spectroscope4 ,all this1 too1 is in keeping with the nebular hypothesis of ,kant and ,laplace so long as this does not assume a primitive infinite dispersion of matter1 but the gathering of matter from finite distances first into nebulous patches which aggregating with each other have given rise to our system of stars4 ,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 heavens1 by a succession of aggregative events1 by hypothesis at intervals of nearly infinite duration1 when the events of the universe had consisted of fitful gleams lighted after eternities of time and extinguished for yet other eternities4 ,finally1 if we seek to replace the eternal instability involved in ,kant's hypothesis when extended over an infinite past1 by any hypothesis of material stability1 we at once find ourselves in the difficulty that from the known properties of matter such stability must have been #bif permanent if ever existent1 which is contrary to fact4 ,thus the kinetic inertia expressed in ,newton's first law of motion might well be supposed to secure equilibrium with material attraction1 but if primevally diffused matter had ever thus been held in equilibrium it must have remained so1 or it was maintained so imperfectly1 which brings us back to endless evolution4 ,on these grounds ,i contend that the present gravitational properties of matter cannot be supposed to have acted for all past duration4 ,universal equilibrium of gravitating particles would have been indestructible by internal causes4 ,perpetual instability or evolution is alike unthinkable and contrary to the phenomena of the universe of which we are cognisant4 ,we therefore turn from gravitating matter as affording no rational account of the past4 ,we do so of necessity1 however much we feel our ignorance of the nature of the unknown actions to which we have recourse4 ,a prematerial condition of the universe was1 we assume1 a condition in which uniformity as regards the average distribution of energy in space prevailed1 but neterogeneity and instability were possible4 ,the realization of that possibility was the beginning we seek1 and we today are witnesses of the train of events involved in the breakdown of an eternal past equilibrium4 ,we are witnesses on this hypothesis1 of a catastrophe possibly confined to certain regions of space1 but which is1 to the motions and configurations concerned1 absolutely unique1 reversible to #big its former condition of potential by no process of which we can have any conception4 ,our speculation is that we1 as spectators of evolution1 are witnessing the interaction of forces which have not always been acting4 ,a prematerial state of the universe was one of unfruitful motions1 that is1 motions unattended by progressing changes1 in our region of the ether4 ,how extended we cannot say2 the nature of the motions we know not2 but the kinetic entities differed from matter in the one important particular of not possessing gravitational attraction4 ,such kinetic configurations we cannot consider to be matter4 ,it was possible to construct matter by their summation or linkage as the configuration of the crystal is possible in the clear supersaturated liquid4 ,duration in an ether filled with such motions would pass in a succession of mere unfruitful events2 as duration1 we may imagine1 even now passes in parts of the ether similar to our own4 ,an endless 7it may be7 succession of unprogressive1 fruitless events4 ,but at one moment in the infinite duration the requisite configuration of the elementary motions is attained2 solely by the one chance disposition the stability of all must go1 spreading from the fateful point4 ,possibly the material segregation was confined to one part of space1 the elementary motions condensing upon transformation1 and so impoverishing the ether around till the action ceased4 ,again in the same sense as the #bih stars are simultaneous1 so also they may be regarded as uniform in size1 for the difference in magnitude might have been anything we please to imagine1 if at the same time we ascribe sufficient distance sundering great and small4 ,so1 too21 will a dilute solution of acetate of soda build a crystal at one point1 and the impoverishment of the medium checking the growth in this region1 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 another4 ,in a similar way the crystallizing out of matter may have given rise1 not to a uniform nebula in space1 but to detached nebula1 approximately of equal mass1 from which ultimately were formed the stars4 ,that an all-knowing ,being might have foretold the ultimate event at any preceding period by observing the motions of the parts then occurring1 and reasoning as to the train of consequences arising from these nations1 is supposable4 ,but considerations arising from this involve no difficulty in ascribing to this prematerial train of events infinite duration4 ,for progress there is none1 and we can quite as easily conceive of some part of space where the same ,infinite ,intelligence1 contemplating a similar train of unfruitful motions1 finds that at no time in the future will the equilibrium be disturbed4 ,but where evolution is progressing this is no longer conceivable1 as being contradictory to the very idea of progressive development4 ,in this case ,infinite ,intelligence #bii necessarily finds1 as the result of his contemplation1 the aggregation of matter1 and the consequences arising therefrom4 ,the negation of so primary a material property as gravitation to these primitive motions of 7or in7 the ether1 probably involves the negation of many properties we find associated with matter4 ,possibly the quality of inertia1 equally primary1 is involved with that of gravitation1 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 liquid4 ,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 vibrations2 so that the newly generated matter1 like the newly formed crystal1 began its existence in a medium richly fed with thermal radiant energy4 ,we may consider that the thermal conditions were such as would account for a primitive dissociation of the elements4 ,and1 again1 we recall how the physicist finds his estimate of the energy involved in mere gravitational aggregation inadequate to afford explanation of past solar heat4 ,it is supposable1 on such a hypothesis as we have been dwelling on1 that the entire subsequent gravitational condensation and conversion of material potential energy1 dating from the first formation of matter to the stage of star formation #cjj may be insignificant in amount compared with the conversion of etherial energy attending the crystallizing out of matter from the primitive motions4 ,and thus possibly the conditions then obtaining involved a progressively increasing complexity of material structure the genesis of the elements1 from an infra-hydrogen possessing the simplest material configuration1 resulting ultimately in such self-luminous nebula as we yet see in the heavens4 ,the late ,james ,croll1 in his ,stellar ,evolution1 finds objections to an eternal evolution1 one of which is similar to the metaphysical objection urged in this paper4 ,his way out of the difficulty is in the speculation that our stellar system originated by the collision of two masses endowed with relative motion1 eternal in past duration1 their meeting ushering in the dawn of evolution4 ,however1 the state of aggregation here assumed1 from the known laws of matter and from analogy1 calls for explanation as probably the result of prior diffusion1 when1 of course1 the difficulty is only put back1 not set at rest4 ,nor do ,i think the primitive collision in harmony with the number of relatively stationary nebula visible in space4 ,the metaphysical objection is1 ,i find1 also urged by ,george ,salmon1 late ,provost of ,trinity ,college1 in favour of the creation of the universe4--7,sermons on ,agnosticism47 ,a4 ,winchell1 in ,world ,life1 says3 ,we have not #cja the slightest scientific grounds for assuming that matter existed in a certain condition from all eternity4 ,the essential activity of the powers ascribed to it forbids the thought2 for all that we know1 and1 indeed1 as the conclusion from all that we know1 primal matter began its progressive changes on the morning of its existence4 ,finally1 in reference to the hypothesis of a unique determination of matter after eternal duration in the past1 it may not be out of place to remind the reader of the complexity which modern research ascribes to the structure of the atom4 #cjb ,,index ,a4 ,abney1 ,sir ,wm41 on sensitisers1 #baj4 ,abundance of life1 numerical1 #ih-ajj4 ,adaptation and aggressiveness of the organism1 #hj4 ,additive law1 the1 with reference to alpha rays1 #bbj4 ,age of ,earth1 comparison of denudative and radioactive methods of finding1 #bc-bi4 ,aletsch glacier1 #bhf4 ,allen1 ,grant1 on colour of ,alpine plants1 #ajd4 ,allen1 ,h4 ,stanley1 on photo-electricity1 #bjc4 ,alpha rays1 nature of1 #bad2 velocity of1 #bad2 effects of1 on gases1 #bad2 range of1 in air1 #bae2 visualised1 #bah2 ionisation curve of1 #baf2 number of1 from one gram of radium1 #bcg2 number of ions made by1 #bcg4 ,alpine flowers1 intensity of colour of1 #ajb4 ,alps1 history of1 #ada2 ,tertiary denudation of1 #adh2 depth of sedimentary covering of1 #adh2 evidence of high pressures and temperatures in1 #adi2 recent theories of formation of1 #aej et seq42 upheaval of1 #adg2 age of1 #adg2 volcanic phenomena attending elevation of1 #adg4 ,andes1 trough parallel to1 #abc2 not volcanic in origin1 #aah4 ,angle of friction on ice1 #bfa-bfe1 #bha-bhc2 on glass1 #bfa-bfe4 ,animate systems1 dynamic conditions of1 #fg2 and transfer of energy1 #ga2 and old age1 #gb2 mechanical imitation of1 #gf1 #gg4 ,animate and inanimate systems compared1 #gc-ge4 ,appalachian range1 formation of1 #abj4 ,arrhenius1 on elevation of continents1 #ag4 ,aryan ,era of ,india1 #acf4 ,asteroids1 probable origin of1 #age2 discovery of1 #age2 dimensions of1 #agf2 orbits of1 #agf2 ,mars' moons derived from1 #agg4 ,b4 ,babbage and ,herschel1 theory of mountain building1 #abc4 ,babes 7and ,cornil71 size of spores1 #ih4 ,becker1 ,g4 ,f41 age of ,earth by sodium collection1 #ad2 age of minerals by lead ratio1 #bj4 ,berthelot1 law of maximum work1 #fb4 ,bertrand1 ,marcel1 section of ,mont ,blanc ,massif1 #aed4 ,beta rays1 nature of1 #bdf2 accompanied by gamma rays1 #bdg2 production of1 by gamma rays1 #bdg2 as ionising agents1 #bdi4 ,biotite1 containing haloes1 #bbc2 pleochroism of1 #bce2 intensified pleochroism in halo1 #bce4 ,body and mind1 as manifestations of progressiveness of the organism1 #hf4 ,boltwood1 age of minerals by lead ratio1 #bj4 ,bose1 theory of latent image1 #bjc4 ,bragg and ,kleeman1 on path of the alpha ray1 #bae2 stopping power1 #bai2 laws affecting ionisation by alpha rays1 #bbj2 curve of ionisation and structure of the halo1 #bcb4 ,brecciendecke1 sheet of the1 #aed4 ,brdche1 sheet of the1 #aed4 ,burrard and ,hayden on the ,himalaya1 #ach2 sections of the ,himalaya1 #aci4 ,c4 ,canals and canali1 #aff2 curvature of1 and path of a satellite1 #ahh et seq42 double and triple accounted for1 #ahf1 #ahg2 doubling of1 #aie2 disappearance and reappearance of1 #aif-aih2 photography of1 #aih2 not due to cracks1 #afg2 not due to rivers1 #afg2 of ,mars1 double nature of1 #aff1 #agj2 crossing dark regions of planet's surface1 #afh2 of ,mars1 ,lowell's views on1 #afh et seq42 shown on ,lowell's map1 investigation of1 #aib et seq42 radiating1 explanation of1 #aic1 #aid2 number of1 #aid2 developed by secondary disturbances1 #aid2 nodal development of1 due to raised surface features1 #aie4 ,chamberlin and ,salisbury1 the ,laramide range1 #aba4 ,clarke1 ,f4 ,w41 estimate of mass of sediments1 #i2 age of ,earth by sodium collection1 #ad2 average composition of sedimentary and igneous rocks1 #db2 on average composition of the crust1 #abf2 solvent denudation of the continents1 #ag1 #dj4 ,claus1 protoplasm the test of the cell1 #fg2 abortion of useless organs1 #fi4 ,coefficient of friction1 definition of1 #bfb2 deduction of1 from angle of friction1 #bfc2 abnormal values on ice1 #bfa-bfe1 #bhb2 for various substances1 #bfe4 ,continental areas1 movements of1 #add4 ,cornil and ,babes1 size of spores1 #ih4 ,croll1 ,james1 dawn of evolution1 #cja4 ,crust of the ,earth1 average composition of1 #abf2 depth of softening in1 #abh4 ,curie1 definition of the1 #bef4 ,d4 ,dana1 on mountain building1 #abj4 ,dawson1 reduction of surface represented by ,laramide range1 #abc4 ,deccan traps1 #acg dferlement1 theory of1 #aee2 explanation of1 #aee et seq42 temperature involved in1 #aef4 ,deimos1 dimensions of1 #agg2 orbit of1 #egg4 ,de ,lapparent1 exotic nature of the ,pralpes1 #aej4 ,de ,montessus and the association of earthquakes with geosynclines1 #adb4 ,denudation as affected by continental elevation1 #ag2 factors promoting1 #cj et seg42 relative activity in mountains and on plains1 #ce-dj2 solvent1 by the sea1 #dj2 the sodium index of1 #df-ej2 thickness of rock-layer removed from the land1 #ea4 ,de ,quincy1 ,system of the ,heavens1 #bjj4 ,dewar1 ,sir ,james1 latent image formed at low temperatures1 #bjb4 ,dixon1 ,h4 ,h41 and ,a,gnadance of ,life1 #fj4 ,double canals1 formation by attraction of a satellite1 #ehe-ahg4 ,douglass1 ,a4 ,e41 observations on ,mars1 #afg4 ,dravidian ,era of ,india1 #ace4 ,e4 ,earth1 early history of1 #c1 #d2 dimensions of1 relative to surface features1 #aag4 ,earth's age determined by thickness of sediments1 #e2 determined by mass of the sediments1 #g2 determined by sodium in the ocean1 #ab2 determined by radioactive transformations1 #ai2 significance of1 #b4 ,earthquakes associated with geosynclincs1 #adb4 ,efficiency1 tendency to maximum1 in organisms1 #aac1 #aad4 ,elements1 probable wide diffusion of rare1 #bcj2 rarity of radioactive1 #bda4 ,elster and ,geitel1 photo-electric activity and absorption1 #bjg2 photo-electric properties of gelatin1 #bab2 ,emanation of radium1 therapeutic use of1 #bef-bei2 advantages of1 in medicine1 #bef2 volume of1 #beg2 how obtained1 #beg2 use of1 in needles1 #beh4 ,equilibrium amount1 meaning of1 #bed1 #bee4 ,evolution and acceleration of activity1 #gi2 of the universe not eternal a pane ante1 #bih4 ,f4 ,faraday and ionisation1 #eg4 ,finality of progress a part1 post1 #bhi4 ,flahault1 experiments on colour of flowers1 #ajh4 ,fletcher1 ,a4 ,l41 proportionality of thorium and uranium1 #bf1 ,g4 ,galileo1 discovery of ,jupiter's moons1 #afb4 ,gamma rays1 nature of1 #bdg3 production of1 by beta rays1 #bdg2 as ionising agents1 #bdi4 ,geddes and ,thomson1 hunger and living matter1 #ga4 ,geiger1 range of alpha rays in air1 #bae2 ionisation affected by alpha rays in air1 #baf2 on scattering1 #bag2 scattering and the structure of the halo1 #bcb4 ,geikie1 ,sir ,a41 uniformity in geological history1 #ae4 ,geosynclines1 #aai2 association with earthquakes and volcanoes1 #adb2 of the tethys1 #adb2 radioactive heat in1 due to sediments1 #acj2 temperature effects due to lateral compression of1 #aca4 ,glacial epoch1 phenomena of1 #bhg4 ,glacier motion1 cause of4 #bhe4 ,glossopteris and ,gangamopteris flora1 #acf4 ,gondwanaland1 #acf4 ,gradient of temperature in ,earth's surface crust1 #abf4 ,h4 ,haimanta period of ,india1 #ace4 ,halley1 ,edmund1 finding age by saltness of ocean1 #ac4 ,hallwachs1 photo-electric activity and absorption1 #bjg4 ,haloes1 pleochroic1 finding age of rocks by1 #ba2 due to uranium and thorium families1 #bbg2 radii of1 #bbg2 over-exposed and underexposed1 #bbh2 intimate structure of1 #bbi et seq42 artificial1 #bbi2 tubular1 in mica1 #bcj2 extreme age of1 #bca2 effect of nucleus on structure of1 #bcb2 inference from spherical form of1 in crystals1 #bcc2 structure of1 unaffected by cleavage1 #bce2 origin of the name pleochroic1#bce2 colouration due to iron1 #bce2 colouration not due to helium1 #bcf2 age ,of1 #bcf2 slow formation of1 #bcg1 #bch2 number of rays required to build1 #bcg2 and age of the ,earth1 #bch-bda4 ,hayden1 ,h4,h41 geology of the ,himalaya1 #acd1 #ach1 #aci4 ,heat-tendency of the universe1 #fb4 ,heat emission from the ,earth's surface1 #abf2 from average igneous rock due to radioactivity1 #abf4 ,helium and the alpha ray1 #bad1 #bbb2 colouration of halo not due to1 #bcf4 ,hering1 ,e41 and physiological or unconscious memory1 #aaa4 ,herschel and ,babbage theory of mountain building1 #abc4 ,herschel1 ,sir ,w41 on galaxy of milky way1 #bic4 ,hertz1 negative electrification discharged by light1 #bjd4 ,himalaya1 geological history of1 #acd-aci4 ,hobbs1 on association of earthquakes and geosynclines1 #adc4 ,holmes1 ,a41 original lead in minerals1 #bj2 age of ,devonian1 #ba4 ,horst concerned in ,alpine dferlement1 objections to1 #aef4 ,hyperion1 dimensions of1 #agg4 ,i4 ,ice1 melting of1 by pressure1 #bfg et seq42 expansion of water in becoming1 #bfg2 lowering of melting-point by pressure1 #bfg2 fall of temperature under pressure1 #bfh et seq42 viscosity of1 #bhd4 ,igneous rocks1 average composition of1 #dc4 ,inanimate actions1 dynamic conditions of1 #fa4 ,inanimate systems1 secondary effects in1 #fc-fe2 transfer of energy into1 #ff4 ,indian geology1 equivalent nomenclature of1 #aci4 ,initial recombination of ions due to alpha rays1 #bba1 #bbb1 #bca2 and structure of the halo1 #bca4 ,insect life in the higher ,alps1 #ajd1 #aje2 destruction of1 on the ,alpine snows1 #ajf4 ,ionisation by alpha ray1 density of1 #bba2 importance in chemical actions1 #bej2 in living cell1 #bej4 ,ions1 number of1 produced by an alpha ray1 #bcg4 ,isostasy1 #ec2 and preservation of continents1 #ec4 ,ivy1 inconspicuous blossoms of1 #ajg2 delay in ripening seed1 #ajg4 ,k4 ,kant and ,laplace1 material hypothesis of1 does not account for the past1 #bij4 ,kelvin1 ,lord1 experiment on effects of pressure on ice1 #bfh-bgj4 ,kleeman and ,bragg4 ,see ,bragg4 ,klopstock introduces skating into ,germany1 #bgc4 ,l4 ,lakes1 cause of blue colour of1 #ee4 ,land1 movements of the1 #ec1 #ed4 ,laukester1 ,ray1 the soma and reproductive cells1 #he4 ,lapworth1 structure of the ,scottish ,highlauds1 #aec4 ,latent heat of water1 #bff4 ,latent image1 formed at low temperatures1 #bjb2 ,bose's theory of1 #bjc2 photo-electric theory of1 #bjd1 #bji et seq4 ,least action1 law of1 #ff4 ,lembert and ,richards1 atomic weight of lead1 #bg4 ,length of life dependent on conditions of structural development1 #ic2 dependent on rate of reproduction1 #id4 ,life-curves of organisms having different activities1 #ib4 ,life1 length of1 #ia4 ,life waves of a cerial1 #ie2 of ,ausaeba1 #hg2 of a species1 #ij4 ,light1 effects of1 in discharging negative electrification1 #bjd2 chemical effects of1 #bje2 experiment showing effect of1 in discharging electrified body1 #bje4 ,lindemann1 ,dr41 duration of solar heat1 #bi4 ,lowell1 ,percival1 observations on ,mars1 #afg et seq42 map of ,mars1 reliability of1 #aih4 ,lucretius1 birth-time of the world1 #a4 ,lugeon1 formation of the ,pralpes1 #aga2 sections in the ,alps1 #aed4 ,lyell1 uniformity in geological history1 #ae4 ,m4 ,magee1 relative areas of deposition and denudation1 #af4 ,mars1 climate of1 #agj2 position in solar system1 #agd1 #age2 dimensions of satellites of1 #agg2 snow on1 #afi2 water on1 #afi2 clouds on1 #afi2 atmosphere of1 #agj2 melting of snow on1 #agj2 dimensions of canals1 #aga2 signal on1 #agb2 times of opposition1 #afd2 orbit of1 #afe2 distance from the ,earth1 #afe2 eccentricity of his orbit1 #afe2 observations of1 by ,schiaparelli1 #afe1 #aff2 ,lowell's observations on1 #afg et seq4 ,maxwell1 ,clerk1 changes made under constraints1 #fe2 on conservation of energy1 #fa4 ,m',connel1 ,j4 ,c41 viscosity and rigidity of ice1 #bhd4 ,memory1 physiological1 #aaa1 #aab4 ,metamorphism1 thermal1 in ,alpine rocks1 #acb1 #adi ,millicurie1 definition of1 #bef4 ,molasse1 accumulations of1 #adh4 ,morin1 coefficients of friction1 #bfe4 ,morphy1 ,h41 experiments on coefficient of friction of ice1 #bha4 ,mountain-building and the geosynclines1 #aai-aba2 conditioned by radioactive energy1 #abe2 energy for1 due to gravitation1 #abb2 reduction of surface attending1 #abc2 depression attending1 #abc2 instability due to thermal effects of compression1 #acb2 igneous phenomena attending1 #acb2 rhythmic character of1 accounted for1 #acc2 movements confined to upper crust1 #abb2 movements due to compressive stresses in crust1 #abb2 movements1 rhythmic character of1 #aba4 ,mountain ranges built of sedimentary materials1 #aah4 ,mller1 ,j41 coefficient of friction of skate on ice1 #bfe1 #bgd4 ,muth deposits of ,india1 #ace4 ,n4 ,newton1 ,professor1 of ,yale1 on origin of ,mars' satellites1 #agg4 ,nucleus1 dimensions of1 #bcg2 amount of radium in1 #bch4 ,nummulitic beds of ,himalaya1 #ach4 ,o4 ,ocean1 amount of rock salt in1 #ej2 cause of black colour of1 #ee2 estimated mass of sediments in1 #dh2 increase of bulk due to solvent denudation1 #eb2 its saltness due to denudation1 #da4 ,old age and death1 #hb-he2 not at variance with progressive activity1 #hc4 ,organic systems1 origin of1 #gh4 ,organic vibrations1 #hf et seq4 ,organism and accelerative absorption of energy1 #gi2 and economy1 #aji-aaa2 and periodic rigour of the environment1 #id1ie4 ,organism and sleep1 #ie2 ultimate explanation of rythmic events in1 #if1 #ig2 law of action of1 #fh et seq42 periodicity of2 and law of progressive activity1 #hb et seq4 ,p4 ,penjal traps1 #ace4 ,pepys and skating1 #bgc4 ,perry1 coefficient of friction of greased surfaces1 #bfe4 ,phobos1 dimensions of1 #agg2 orbit of1 #agg4 ,photoelectric activity and absorption1 #bjg2 persists at low temperatures1 #bjh1 #bji2 not affected by solution1 #bac4 ,photo-electric experiment1 #bje2 sensitiveness of the hands1 #bjg2 theory of latent image1 #bjd1 #bji et seq4 ,photographic reversal1 experiments on1 by ,wood1 #baa2 theory of1 #baj4 ,piazzi1 discovery of first ,asteroid1 #age4 ,pickering1 ,w4 ,h41 observations on ,mars1 #afg4 ,planet1 slowing of axial rotation of1 #ahi4 ,plant1 expectant attitude of1 #aji4 ,pleochroic haloes1 measurements of1 #bbd2 theory of1 #bbd et seq42 true form of1 #bbf2 radius of1 and the additive law1 #bbe2 absence of actinium haloes1 #bbe2 see also ,haloes2 mode of occurrence of1 #bbc et seq4 ,poole1 ,j4 ,h4 ,j41 proportionality of thorium and uranium1 #bf4 ,poulton1 uniformity of past climate1 #ag4 ,pratt1 ,archdeacon1 and isostasy1 #ec4 ,pralpes1 exotic nature of1 #aej1 #aea4 ,prematerial universe1 nature of a1 #big1 #cjj4 ,prestwich and thickness of rigid crust1 #abh2 history of the ,pyrenees1 #adj4 ,primitive organisms1 interference of1 #hi2 life-curves of1 #hh4 ,proctor and orbits of ,asteroids1 #agf4 ,protoplasm1 encystment of1 #fh4 ,purana ,era of ,india1 #acd4 ,pyrenees1 history of1 #adj4 ,r4 ,radioactive elements concerned in mountain building1 #abe4 ,radioactive layer1 failure to account for deep-seated temperatures1 #abg2 assumed thickness of1 #abh2 temperature at base of1 due to radioactivity1 #abi2 in the upper crust of the ,earth1 #abe2 thickness of1 #abf-abh4 ,radioactive treatment1 physical basis of1 #bea4 ,radioactivity and heat emission from average igneous rock1 #abf2 rarity of1 established by haloes1 #bda1 #bdc4 ,radium1 chemical nature and transmutation of1 #bdd-bde2 emanation of1 #bde2 rays from1 #bec1 #bed2 table of family of1 #bec2 period of1 #bec2 small therapeutic value of1 #bed4 ,radium ,c1 therapeutic value of1 #bed2 rays from4 #bed2 generation of1 #bed4 ,rationality1 conditions for development of1 #afc4 ,rays1 similarity in nature of gamma1 ,x1 and light rays1 #bdh2 effects on living cell1 #bea2 penetration of1 #bea4 ,reade1 ,t4 ,mellard1 finding age of ocean by calcium sulphate1 #ac4 ,recumbent folds1 formation of1 #aee et seq4 ,regelation1 #bhd2 affecting glacier motion1 #bhe4 ,reversal1 photographic1 explanation of1 #baa4 ,richards and ,lembert1 atomic weight of lead1 #bg4 ,richter1 ,jean ,paul1 ,dream of the ,universe1 #bjj4 ,rock salt in the ocean1 amount of1 #ac4 ,rocks1 average composition of1 #dc2 radioactive heat from1 #abf2 rate of solution of1 #cf4 ,russell1 ,i4 ,c41 river supply of sediments1 #aj4 ,rutherford1 ,sir ,e41 determination of age of minerals1 #ai1 #bj2 age of rocks by haloes1 #bb2 derivation of actinium1 #bbf2 artificial halo1 #bbi2 number of alpha rays from one gram of radium1 #bcg4 ,s4 ,salt range deposits of ,india1 #acd4 #ace4 ,saltness of the ocean due to denudation1 #da-df4 ,salisbury 7and ,chamberlin71 the ,larimide range1 #aba4 ,salmon1 ,rev4 ,george1 on creation1 #cja4 ,satellite1 velocity of1 in its orbit1 #aia2 method of finding path of1 over a rotating primary1 #ahi et seq42 direct and retrograde1 #agh2 ultimate end of1 #agh2 path of1 when falling into primary1 #agi2 effect of ,mars' atmosphere on infalling satellite1 #agi2 stability of close to primary1 #ahj2 effects of1 on crust of primary1 #ahj et seq4 ,schiaparelli1 observations on ,mars1 #afe #aff4 ,schmidt1 ,c41 original depth of ,alpine layer1 #aca-adh2 structure of the ,alps1 #aeb4 ,schmidt1 ,g4 ,c41 on photo-electricity1 #bjg1 #bjh2 effect of solution on photo-electric activity1 #bac4 ,schuchert1 ,c41 average area of ,n4 ,america during geological time1 #af4 ,sedimentary rocks1 average composition of1 #dc2 mass of1 determined by sodium index1 #dg4 ,sedimentation a convection of energy1 #acc4 ,sediments1 average river supply of1 #aa2 on ocean floor1 mass of1 #dh2 average thickness of1 #di2 precipitation of1 by dissolved salts1 #ef-eh2 radioactivity of #acj2 radioactive heat of1 influential in mountain building1 #acj1 #aca2 rate of collecting1 #g2 determination of mass of1 #h2 river supply of1 #aj2 total thickness of1 #f4 ,semper1 energy absorption of vegetable and animal systems1 #gh4 ,sensitisers1 effects of low temperature on1 #baj4 ,simplon1 radioactive temperature in rocks of1 before denudation1 #acb4 ,skates1 early forms of1 #bgc2 principles of construction of1 #bgc et seq42 action of1 on ice1 #bgf2 bite of1 #bgh-bhj4 ,skating not dependent on smoothness of ice1 #bfj2 history of1 #bgc4 ,skating only possible on very few substances1 #bgi4 ,soddy1 ,f41 on isotopes1 #bd4 ,sodium1 deficiency of1 in sediments1 #dd2 discharge of rivers1 #ad4 ,soils1 formation of1 #cg-ci2 surface area exposed in1 #ci4 ,sollas1 ,w4 ,j41 age of ,earth by sodium in ocean1 #ad2 thickness of sediments1 #f4 ,spencer1 on division of protoplasm1 #fg4 ,spores1 number of molecules in1 #ig4 ,stevenson1 ,dr4 ,walter ,c41 and technique of radioactive treatment1 #bei4 ,stoletow1 photo-electric activity anal absorption1 #bjg4 ,stopping power of substances with reference to alpha rays1 #bai4 ,struggle for existence1 dynamic basis of1 #hj4 ,strutt1 ,prof4 the ,hon4 ,r4 ,j41 age of geological periods1 #bj2 radioactivity of zircon1 #bbc4 ,sub-,apennine series of ,italy1 #adh4 ,suess1 nature of earthquakes4 #adc4 ,survival of the fittest and the organic law1 #hj4 ,t4 ,talchir boulder-bed1 #acf4 ,temperature gradient in ,earth's crust1 #abf4 ,termier1 section of the ,pelvoux ,massif1 #bed4 ,tethys1 early extent of1 #ace-acg2 geosynclines of1 #adb4 ,thermal metamorphism in ,alpine rocks1 #acb1 #adi4 ,thomson1 ,james1 prediction of melting of ice by pressure1 #bfg4 ,thorium and uranium1 proportionality of1 in older rocks1 #bf4 ,triple canals1 formation of1 by attraction of a satellite1 #ahg4 ,tyndall1 colour of ocean water1 #ee4 ,u4 ,uniformitarian view of geological history1 #ae-ah4 ,universe1 simultaneity of the1 #bic-bie4 ,uranium-radium family of elements1 table of1 #bec4 ,v4 ,val d',hrens1 earth pillars of1 #cc4 ,van ,tillo1 nature of continental rock covering1 #i4 ,vegetable and animal systems1 relative absorption of energy of1 #gh4 ,vegetative organs1 struggle between1 #aje1 #ajf4 ,volcanoes and mountain ranges1 #aah2 associated with geosynclines1 #adb2 ,oligocene and ,miocene of ,europe1 #adg4 ,w4 ,weinschenk and thermal metamorphism1 #acb1 #adi4 ,weismaun1 encystment of protoplasm1 #fh2 length of life and somatic cells1 #if2 origin of death1 #hc2 tendency to early reproductiveness1 #ih4 ,wilson1 ,c4 ,t4 ,r41 visualised alpha rays1 #bah4 ,winchell1 progressive changes of matter not eternal1 #cjb4 ,wood1 ,r4 ,w41 on photographic reversal1 #baa4 ,z4 ,zircon1 radioactivity of1 #bbc2 as nucleus of halo1 #bbc4