Sir A. Geikie—Age of the Earth. 459 



When Lord Kelvin first developed his strictures on modern 

 geology he expressed his opposition in the most uncompromising 

 language. In the short paper to which reference has already been 

 made, he announced, without hesitation or palliation, that he 

 "briefly refuted " the doctrine of Uniformitarianism which had been 

 espoused and illustrated by Lyell and a long list of the ablest 

 geologists of the day. The severity of his judgment of British 

 geology was not more marked than was his unqualified reliance 

 on his own methods and results. This confident assurance of 

 a distinguished physicist, together with a formidable array of 

 mathematical formulas, produced its eflfect on some geologists and 

 palseontoiogists who were not Gallios. Thus, even after Huxley's 

 brilliant defence, Darwin could not conceal the deep impression 

 which Lord Kelvin's arguments had made on his mind. In one 

 letter he wrote that the proposed limitation of geological time was 

 one of his "sorest troubles." In another, he pronounced the physicist 

 himself to be "an odious spectre." ^ 



The same self-confidence of assertion on the part of some, at least, 

 of the disputants on the physical side has continued all through the 

 controversy. Yet when we examine the three great physical 

 arguments in themselves, we find them to rest on assumptions 

 which, though certified as " probable " or " very sure," are never- 

 theless admittedly assumptions. The conclusions to which these 

 assumptions lead must depend for their validity on the degree of 

 approximation to the truth in the premises which are postulated. 



Now it is interesting to observe that neither the assumptions nor 

 the conclusions drawn from them have commanded universal assent 

 even among physicists themselves. If they were as self-evident as 

 they have been claimed to be, they should at least receive the loyal 

 support of all those whose function it is to pursue and extend the 

 applications of physics. It will be I'emembered, however, that 

 thirteen years ago Professor George Darwin, who has so often 

 shown his inherited sympathy in geological investigation, devoted his 

 presidential address before the Mathematical Section of this Associa- 

 tion to a review of the three famous physical arguments respecting 

 the age of the earth. He summed up his judgment of them in the 

 following words: — "In considering these three arguments I have 

 adduced some reasons against the validity of the first [tidal friction] ; 

 and have endeavoured to show that there are elements of uncertainty 

 surrounding the second [secular cooling of the earth] ; nevertheless 

 they undoubtedly constitute a contribution of the first importance to 

 physical geology. Whilst, then, we may protest against the 

 precision with which Professor Tait seeks to deduce results from 

 them, we are fully justified in following Sir William Thomson, who 

 says that ' the existing state of things on the earth, life on the 

 earth — all geological history showing continuity of life, must be 

 limited within some such period of past time as 100,000,000 years.' " ^ 



More recently Professor Perry has entered the lists, from the 



1 Darwin's Life and Letters, vol. iii, pp. 115, 146. 



2 Rep. Brit. Assoc, 188G, p. 517. 



