July 19, 1921 clarke : evolution of matter 297 



But it does not always follow that the first interpretation is the only- 

 one possible, nor even that it is the best. Now it seems to me con- 

 ceivable, that the lines of Aston's mass spectra may really belong 

 to decomposition products of the elements, produced by the disinte- 

 grating effect of the positive rays. This conclusion, I think, is more in 

 harmony with chemical evidence than the one first proposed. It 

 is, furthermore, sustained by the fact that the elements of high atomic 

 weight seem to show as a rule more lines in their mass spectra than 

 those low in the scale. The most complex elements should undergo 

 the largest amount of disintegration. If the atomic weights as 

 actually determined by the best modern methods are mere statistical 

 averages of widely differing figures, then the elements must be re- 

 garded as variable mixtures, and uniformity could hardly be expected. 

 This lack of uniformity would extend to all chemical compounds, 

 which should vary in composition and also in physical properties; 

 all chemical calculations would become inexact, and even the spectra 

 of the elements would lose much of their significance. Chaos would 

 rule instead of order. 



In point of fact the evidence in favor of definiteness of atomic 

 weight is much better than anything which has been adduced to the 

 contrary. On that subject I could make a strong argument in support 

 of my position; but I do not care to overload this paper with details. 

 In discussing the evolution of the elements, and also their decay, 

 I must take a pragmatic position and assume their integrity. Their 

 evolution follows an upward path, with which the downward path 

 of decomposition is approximately but not exactly parallel. The 

 two paths, however, coalesce in the region of hydrogen, nebulium, 

 and helium; and so the beginning and the end are the same. That 

 hydrogen and helium are the chief constituents of the elements as 

 we know them is possible, as Harkins in a long series of interesting 

 papers has attempted to show. I cannot accept all his conclusions 

 as final, although he has at least discovered some interesting rela- 

 tions. Nebulium should not be left out of account. 



On the mechanism of the process by which the elements were 

 built up I have nothing definite to say. I can only ask questions. 

 If a heavy atom, like that of gold or mercury, is formed from simpler 

 atoms, how are the latter changed? What happens to their nuclei 

 and their electrons? Is the structure of the carbon atom the same 

 in graphite and in diamond? Here the tetrahedral atom which 

 plays so important a part in stereochemistry has to be considered. 



