102 



KNOWLEDGE. 



[Apbil 1, 1897. 



and difBculties, this berth, though the salary was small, 

 suited him entirely, and afforded that opportunity for 

 which his thirst for knowledge craved — the free use of a 

 valuable library. Here he read the researches of Faraday, 

 Joule, Thomson, Tyndall, Rankiue, Darwin, and others. 

 In the spring of 1.S64, Croll independently conceived that 

 the change in the eccentricity of the earth's orbit might 

 be the real cause of the glacial epoch— a subject which at 

 the time was being discussed by geologists— and he wrote 

 a paper expressing his views, which was published in the 

 P/iihAsiipliiciil ]\[aiffi:ine fov August, 1864. The originality 

 of the ideas advanced attracted much attention, among 

 the men of note who appreciated the new departure being 

 Sir Archibald Geikie, who invited Croll to join the Scottish 

 Geological Survey, on the reorganization of the service in 

 1867. Croll, who was then forty-six years of age, had to 

 submit to the indignity of being plucked by the Civil 

 Service Commissioners because he did not succeed in 

 totting long columns of figures and writing neatly like a 

 young lad fresh from school ; but the wooden rules of red- 

 tapeism were ultimately relaxed on the strong recommen- 

 dation of Geikie, i^iurchison, and Thomson, to accept 

 Croll's great calculations regarding the eccentricity of the 

 earth's orbit and the precession of the equinoxes during 

 the last ten million years as sufficient evidence of his 

 capacity for figui-es, and big papers published in scientific 

 journals as proof of his ability to write tolerable English. 

 He accordingly entered the service on September 2nd, 

 1867, and for thirteen years conducted the correspondence 

 with the men in the field, supplied them with necessary 

 maps, instruments, and stores, etc., from a central ofBce 

 in Edinburgh — duties which were physically and mentally 

 of a light character, and consequently admitted of his 

 continuing his own private investigations in speculative 

 philosophy. Eetiring from active service in 1881, he 

 lingered on till the loth December, 1890, writing a little 

 as he was able. Such is a brief outline of Dr. Croll's life. 

 He was throughout his career a toiler for daily bread ; 

 all his purely scientific work being of the nature of a 

 hobby, and not in any sense a profession or means of 

 augmenting his resources from a pecuniary point of view. 



Dr. Croll's first literary work of any pretension was 

 " The Philosophy of Theism," 1857, a volume published 

 anonymously, and the object of which was, not to prove 

 the existence of God, but to investigate the method to be 

 pursued in order to arrive at a proof of His existence. It is 

 worthy of note that Dr. Cairns predicted that the unknown 

 writer needed only to give himself entirely to this topic — 

 or any other — to achieve distinguished success, his style 

 being conspicuous for dignity, manliness, and translucency. 

 During the next few years he contributed several interesting 

 papers to the press, which showed that he was busily 

 occupied in thinking out for himself some of the great 

 scientific problems of the day ; but it is to the year 1801 

 that we must look for the initial point in that brilliant 

 career which he ultimately carved out for himself. His 

 scientific papers maybe divided into six groups : (1) Early 

 Physical Papers; (2) "Age and Origin of the Sun"; 

 (8) " Geological Climate and Chronology"; (1) " Glacial 

 Epoch and Glaciers" ; (5) " Ocean Currents" ; (G) Mis- 

 cellaneous Papers. 



A few words from Prof. Tyndall in reply to Croll, who 

 had submitted one of his papers, will convey some idea of 

 the value of the latter's physical investigations : — " Your 

 letter was interesting to me as an illustration of power to 

 seize a definite physical image : the molecules acting as 

 hammers was capital." On another occasion, after sending 

 his paper "On Supposed Objections to the Dynamical Theory 

 of. Heat," Croll received this reply: "The very experiment 



to which you refer, of rendering a body hot by concussion, 

 is the one which most influenced my conviction that it 

 was possible to produce incandescence by invisible rays." 



Dr. Croll, in his paper " On the Physical Cause of the 

 Change of Climate during Geological Epochs," summarized 

 the theories then in vogue, and declared them to be 

 insufficient to account for the magnitude of the results. 

 He then discussed the effects of changes in the eccentricity 

 of the earth's orbit, both directly and indirectly, but 

 showed that a lack of data prevented any very definite 

 conclusions being drawn. By means of Leverrier's 

 formula;, he calculated tables of eccentricity for three 

 million years in the past and one million years in the 

 future, with the view of determining the periods of high 

 eccentricity which, according to his theory, were coincident 

 with cycles of extreme cold. The late Sir Andrew 

 Eamsay was one of the very first to perceive the 

 importance of Croll's paper, and, quite unknown to 

 the author, he wrote, lOfch August, IsOl : "I have just 

 read your article . . . and am very much struck with 

 your views. . . . If your theory be true, we may have 

 at length some hope of being able to measure geological 

 time. ... I was delighted to find the statement so 

 plainly put." In the four million years included in Croll's 

 computations three epochs of high eccentricity were 

 apparent, and at the one which occurred eight hundred and 

 fifcy thousand years ago he concluded that the Gulf Stream 

 could not have been more than half its present volume. 

 The midwinter temperature of Scotland would be 45-3° P. 

 lower than at present, owing to the greater distance from 

 the sun, while, the Gulf Stream would cause a further 

 diminution of 14^ F., giving a total diminution of 59-3 F. 

 below the present midwinter temperature of 39^ F. Thus 

 the midwinter temperature of Scotland eight hundred and 

 fifty thousand years ago was —20-3 F. If glacial con- 

 ditous occur when the eccentricity is great, then there is a 

 possibility of correlating these ice epochs with definite 

 dates ; and when the dates of the most recent glacial 

 epochs are fixed, the approximate age of the other ejoocha 

 and events of the earth's evolution can be estimated. 



By another process of reasoning. Dr. Croll studied the 

 origin and age of the sun, and he was disposed to fix the 

 limit at one hundred million years. In seeking to 

 establish the age of the stratified rocks, he based his 

 estimates on the known rates at which the Mississippi 

 carries sediment into the ocean. This fairly typical river 

 removes one foot from the surface of the land in six 

 thousand years. By this process of denudation, continents 

 are cut up into islands, and these again into smaller tracts, 

 till the whole finally disappears. In his " Stellar Evo- 

 lution," Croll elaborated a theory of the origin of suns and 

 systems which has at least secured the approval of many 

 eminent astronomers, and will find a place in the history 

 of astronomical speculation for long years, if not for all 

 time. In his last work, " The Philosophical Basis of 

 Evolution," he concludes that the universe, in all its 

 beauty, joy, and fulness of life, can never be explained in 

 terms of matter, motion, and force ; so that the whole 

 process of evolution, natural selection included, evidently 

 points to Theism. The argument, as far as it goes — so 

 says his biographer — is simply irresistible. 



The irony of fa te is nowhere more poignantly apparent 

 than in the story of this truly great philosopher's life, as 

 narrated and illustrated by the happily interpolated letters 

 from the most eminent contemporary men of science in 

 these pages. Mr. James Campbell Irons has indeed 

 produced a very realistic picture of a beautiful and useful 

 life — a life which from every point of view was strikingly 

 uncommon, pure, intellectual, noble, and generous. Mr. 



