DISSENTIENT PHYSICISTS 211 



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 nevertheless admittedly assumptions. The con- 

 clusions to which these assumptions lead must deoend 

 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 physi- 

 cists 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 phvsics. It will 

 be remembered, however, that thirteen years ago Pro- 

 fessor George Darwin, who has so often shown his 

 inherited sympathy in geological investigation, devoted 

 his presidential address before the Mathematical Section 

 of this Association to a review of the three famous 

 physical arguments respecting the age of the earth. 

 He summed up his judgment of them in the folio 

 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 



