414 SEE— THE NEW THEORY OF EARTHQUAKES [November 15, 



nomena noticed about the islands in the sea. It happens also that 

 some islands once built around by coral are again upraised by a 

 recurrence of the elevating movement ; yet this probably v^ould not 

 be the usual phenomenon, so that in general Darwin's observations 

 on coral reefs accord with the theory, and are what one might nat- 

 urally expect to find on an ocean-covered planet with leaky and 

 oscillating crust. 



§ 25. On the Modification of Secular Cooling by Radium. — In 

 regard to the age of the earth, it ought to be remarked that if radium 

 be taken into account, the heat resulting from its secular disintegra- 

 tion would prevent the crust from thickening, except very slowly; 

 and consequently with so thin a crust as that of our actual globe 

 the period of time since the consolidation, as calculated in the paper 

 on the " Temperature of the Earth," is too small. Accordingly 

 although we found the period to be of the order of ten million years, 

 yet if radium be introduced the duration of time might be lengthened 

 to one hundred million years, or even to a greater period. And if 

 this energy due to radium be admitted for the earth, it could not 

 well be denied for the sun, so that the period of the sun's activity 

 would be lengthened correspondingly. Hence the more moderate 

 of the immense periods of time demanded by geological phenomena 

 may be conceded. Time must decide to what extent these demands 

 are justifiable. At present we may await future developments with 

 entire confidence that the causes now known are sufficient to explain 

 all terrestrial phenomena. 



§ 26. Favorable Reception of the Present Theory by Physicists 

 and Geologists. — The lively interest awakened by the two preceding 

 papers among physicists and geologists and other men of science, 

 as shown by letters which have reached the writer, indicates a much 

 more favorable reception of the present theory than might have been 

 anticipated. Indeed its general acceptance seems fully assured, and 

 many questions are thus raised of great importance in natural phi- 

 losophy. All who have considered the question attentively seem to 

 agree that it is very improbable that the ocean bottom is water- 

 tight. One of the most eminent of living physicists expresses the 

 opinion that this cannot be true, unless the nature of the rock is 

 greatly modified by pressure. Such modification under pressure he 



