458 SCIENCE PROGRESS 



neither of them seemed to have gripped the problem. Mr. 

 Holmes tried to give reasons for thinking that uranium, one of 

 the heaviest known substances, would not be found in the interior 

 of the Earth, but would be concentrated in the outer layer. His 

 argument was based on its distribution in the acid and basic 

 rocks of the Earth's crust. He put forward as speculative the 

 idea that radioactive decay might be inhibited by great heat and 

 pressure. I think there can be no doubt that the first idea is 

 the more speculative of the two. By what conceivable means 

 could radioactive matter be concentrated in the crust to the 

 degree required by theory ? On the other hand, if we admit 

 that external conditions can inhibit radiochemical action, why 

 should it not be reversed ? Ordinary chemical actions are re- 

 versible, given the necessary change of conditions. I do not 

 mean to suggest that uranium would be built up from radium 

 and emanation, merely that it would be synthesised from other 

 elements given the necessary conditions. 



On the question of the speculative nature of the suggestion, 

 it must be admitted that, in a sense, speculative it is. We have 

 never been able, by artificial means, to vary the rate of radio- 

 active decay. But, so far as reasoning can be applied to such 

 matters, what inference is simpler ? Uranium compounds are 

 continually and slowly decaying at a constant rate. It is, 

 therefore, a temporary element. And a temporary element must 

 have had a beginning. The argument is as sound for uranium 

 as for radium. The time scale only is altered. On the sup- 

 position that the rate of decay is a constant quantity, an 

 origin of uranium is a necessary inference. If this is not the 

 origin, what is? 



Scientific men are often slow to appreciate the simple and 

 natural inferences from their discoveries. Is not the fact that 

 uranium and radium are elements in every sense but one a 

 clear indication that other elements are not elements in the old- 

 fashioned sense, but that they could be more correctly described, 

 as some one has suggested, as chemical primaries? 



The necessity for some such idea can be found in other 

 departments of science. As I have indicated elsewhere, 1 it is 



1 See Contemporary Review, June 1913, "On the Age of the Sun's Heat"; 

 Knowledge, Jan. 1910, " A Theory of the Structure of the Solar Photosphere." An 

 article by the Messrs. Jessup, in the Philosophical Magazine, January 1908, 

 though not directly dealing with the problem, is of interest in the same connection. 



