GENESIS OF THE ELEMENTS 167 



which a is the atomic weight of the first member and d a common 

 difference, seems to represent their true relations to one another, 

 thus : 



a = 7 =Li 



a-fd = 7+16=23=Na 



a+2d=23+16=39=K, etc. 



This was the idea of Dumas three-quarters of a century ago. 



In any discussion as to the mode in which the elements may 

 have been evolved this principle must be borne in mind. It 

 leads to the conclusion that in certain families of the elements 

 the successive terms have been produced by a process which, 

 after the formation of the first term, is continued by successive 

 condensations of similar matter on the first as a nucleus. 



In other cases it may be supposed that the process was dis- 

 turbed in some way before completion, so that the result may be 

 carried along two or more independent lines. The case of the 

 metals allied to iron may be taken as an example. They are 

 probably all derived from aluminium as a basis somewhat as 

 follows : 



Al (27) 

 I 



I I I I 



So (44) Mn (55) Fc (56) Ga (70) 



Y (89) Co (59) Ni (587) In (115) 



La (139) ? Cu (63) Tl (204) 



As to the radio-active elements some have been formed by 

 disintegration of others of greater atomic weight, while some 

 may have been produced by condensation of a less deliberate 

 character than usual, so that an unstable internal arrangement 

 of electrons resulted with production of an endothermic atom. 



Helium is known to be derived from radium. Hence it seems 

 reasonable to suppose that argon and the rest which are found 

 only in very minute quantity in the atmosphere, and not in 

 minerals, may have originated in a corresponding disruption of 

 more complex atoms of elements which had only a temporary 

 existence, and have long disappeared from among terrestrial 

 materials. 



It is obvious, however, that here we reach almost the limit of 

 legitimate speculation. There can be no doubt that much 

 further light may be expected as the result of the experimental 

 researches which are going on, and to allow the imagination to 



