460 Notices of Memoirs — British Association — 



pliysical side, to challenge the validity of the conclusions so 

 confidently put forward in limitation of the age of the earth. He 

 has boldly impugned each of the three physical arguments. That 

 which is based on tidal retardation, following Mr. Maxwell Close 

 and Professor Darwin, he dismisses as fallacious. In regard to the 

 argument from the secular cooling of the earth, he contends that it is 

 perfectly allowable to assume a much higher conductivity for the 

 interior of the globe, and that this assumption would vastly increase 

 our estimate of the age of the planet. As to the conclusions drawn 

 from the history of the sun, ho maintains that, on the one hand, the 

 sun may have been repeatedly fed by infalling meteorites, and that 

 on the other the earth, during former ages, may have had its heat 

 retained by a dense atmospheric envelope. He thinks that " almost 

 anything is possible as to the present internal state of the earth," and 

 he concludes in these words : " To sum up we can find no published 

 record of any lower maximum age of life on the earth, as calculated 

 by physicists, than 400 millions of years. From the three physical 

 arguments, Lord Kelvin's higher limits are 1,000, 400, and 500 

 million years. I have shown that we have reasons for believing 

 that the age, from all these, may be very considerably underestimated. 

 It is to be observed that if we exclude everything but the arguments 

 from mere physics, the pr oh able age of life on the earth is much less 

 than any of the above estimates ; but if the paleontologists have 

 good reasons for demanding much greater times, I see nothing 

 from the physicist's point of view which denies them four times the 

 greatest of these estimates." ^ 



This remarkable admission from a recognized authority on the 

 physical side re-echoes and emphasizes the warning pronounced by 

 Professor Darwin in the address already quoted — "at present our 

 knowledge of a definite limit to geological time has so little 

 precision that we should do wrong to summarily reject any theories 

 which appear to demand longer periods of time than those which 

 now appear allowable."" 



This ' wrong ' which Professor Darwin so seriously deprecated 

 has been committed not once, but again and again, in the history of 

 this discussion. Lord Kelvin has never taken any notice of the 

 strong body of evidence adduced by geologists and palaeontologists 

 in favour of a much longer antiquity than he is now disposed to 

 allow for the age of the earth. His own three physical arguments 

 have been successively restated, with such corrections and modi- 

 fications as he has found to be necessary, and no doubt further 

 alterations are in store for them. He has cut off slice after slice 

 from the allowance of time which at first he was prepared to grant 

 for the evolution of geological history, his latest pronouncement 

 being that "it was more than twenty and less than forty million 

 years, and probably much nearer twenty than forty." ^ But in none 



1 Nature, vol. li, p. 585 (April 18, 1895). 

 * Eep. Brit, Assoc. 1886. p. 518. 



' " The Age of the Earth," Presidential Address to the Victoria Institute for 1897, 

 p. 10 ; also in Phil. Mag., January, 1899. 



