356 SCIENCE PROGRESS 



Certainly it is not mine. My idea is that the radioelements and the nebular 

 elements are both less stable than those commonly found in the crust of the 

 Earth, and than those the lines of which are found in the spectra of stars 

 approaching extinction. Mr. Holmes will find greater detail in the articles to 

 which he refers, and would do well to read them with the presupposition that 

 (with the exception of three lines obviously recast by the printer by the light of 

 nature) they are intended to mean what they say. I would add also that if 

 Mr. Holmes attributes to the experiments of Boltwood on lead ratios, which he 

 has repeated and extended, any validity whatever, he is bound to adopt some 

 hypothesis of the kind to account for the duration of solar heat. Certainly the 

 hypothesis, as stated by me, whatever criticisms may be made, is not contrary to 

 any recognised and valid law of chemical reaction. 



The present note provides an opportunity for me to modify a statement made 

 in my last article on geologic time. 1 In that article I stated that Prof. F. W. 

 Clarke had expressed doubts concerning the validity of Prof. Joly's theories of 

 geologic time based on the amount of sodium in the sea. That statement is 

 strictly accurate. 2 I have just discovered that, more recently, he has practically 

 identified himself with Prof. Joly's views, 3 by a strange coincidence, at a time 

 when Prof. Joly shows signs of abandoning them. I, therefore, make the cor- 

 rection. The argument of the article, however, stands, and I shall be greatly 

 interested to discover that either Prof. Clarke, or Prof. Joly, or any one else can 

 answer it. Prof. Clarke seemingly places no value whatever on radioactive 

 methods of investigation. 



1 This Journal, July 1914, p. 57. 



- Data of Che?>iistry, 1st edition, p. no. 



3 lb. 2nd edition, p. 138 and elsewhere. 



H. S. Shelton. 



