32 Messrs. A. 0. and A. E. Jessup on the 
monovalent element, that is to say the outer ring of corpuscles 
belonging to hydrogen contains one free electron, the whole 
constituting a stable system. We have already stated that 
the tendency of the electron is to form into stable groups of 
eight, consequently we may view the single free electrons of 
hydrogen as being possessed with a definite and measurable 
desire to complete its system of eight. It appears that in 
order to do this it adds on first a single group of eioht 
electrons. The result of this would be that the free electron 
on the hydrogen atom completes its system of eight, and that 
one electron will still be left over in the free state. This 
addition of systems of eight electrons goes on continuously 
until the next position of maximum stability is reached. This, 
however, as we have before shown, represents the element 
lithium. Now inasmuch as the addition of each group of 
eight electrons in adding itself on, forms with the free 
electrons already existing a stable group of eight, and leaves 
still one free electron on the outside, so now we see that each 
evolution product thus normally produced must have the same 
valency as the antecedent element. We therefore find that 
lithium and all the elements normally produced from hydrogen 
must be monovalent. Now without binding ourselves clown 
in any way to the actual shape of these rings, we do assume 
that there is some intimate connexion between the valency of 
a ring and its shape. We therefore point out that in the 
process of evolution from hydrogen each ring and corpuscle 
takes on the same shape as the outer ring of the hydrogen 
atom ; that is to say, that the rings of all the alkali metals 
have that shape which is typical of the ring of the hydrogen 
atom. Now this addition of rings of the same type as the 
previously existing rings is what we have already spoken of 
as the principle of heredity, that is to say, in all normal 
processes of evolution there is definite evidence of an hereditary 
principle, inasmuch as every valent element possesses the 
same shape and valency as that of its antecedent element. 
Now this process of evolution, which we have described in 
detail in the case of the alkali metals, we consider to be per- 
fectly general throughout the whole of the Periodic Table, in 
so far as what we have called " direct evolution " is concerned. 
This normal process of evolution takes place undoubtedly in 
the first three families, and in the last family of our Table. 
The next point we have to deal with, is what we have 
previously defined as " indirect evolution " ; that is to say, 
when series of elements of valency differing from that of the 
parent family are produced. In the case of the first group 
of alkali metals, the members of this family are amongst the 
