Constitution and Stability oj Atom Nuclei. 311 



particle, from which the nucleus is built, and not wholly by 

 the stability of the group aggregate, so this possibility 

 should be kept in mind in connexion with the considerations 

 concerning this problem introduced later in this paper. 



Previous to the development of the newer theory con- 

 cerning the relative abundance of the chemical elements and 

 of the atomic species in the years 1915 to 1917, it was 

 generally assumed, in so far as the subject was treated at all,, 

 that the most important factors in establishing the particular 

 abundance relations found in the earth's crust are those in 

 which the chemical and physical properties are effective 

 in producing segregation. While it is true that these factors 

 are of importance and should always be taken into consider- 

 ation, it is also true that the correlations between the 

 abundance relations and those concerning nuclear com- 

 position, are much more numerous and prominent than those 

 between the abundance and the Mendelejeff periodic system, 

 which is a general expression of the physical and chemical 

 relations of the chemical elements. 



In studying the relative abundance of the different atomic 

 species the ideal method would be to sample one, or preferably 

 more, solar systems at the desired stage of evolution, and to 

 make a quantitative analysis for all of the isotopes of all of 

 the 92 elements in the system of elements as it is now 

 known. Since it is at present impossible to do this, or even 

 to obtain a representative quantitative analysis of the material 

 of the earth, it might be thought that sufficiently good data 

 could be obtained from the earth's crust or the lithosphere. 



However, there are several important factors which cause 

 our knowledge of the quantitative composition of the earth's 

 crust to be of much less value for the solution of our 

 problem than it might seem to possess on first thought. In 

 the first place the quantitative analyses which have been 

 made represent the composition of only the mere skin of the 

 earth, the depth of which does not exceed the ten to twenty 

 miles caused by geologic displacements. The surface of the 

 earth has been markedly influenced both by igneous processes 

 which have resulted in maomatic differentiation, and bv 

 weathering, solution, and redeposition. 



If the sun is next considered it is found that although a 

 large area of its surface is exposed to us for spectroscopic 

 investigation, the spectroscope gives no accurate measure of 

 the quantitative composition, and that its findings are also 

 influenced by the fact that it is only the surface and not the 

 interior which is visible. 



There is, however, material available, of which accurate 



