412 
Conclusion 
[CH. XVII 
cosmogony to-day. It seems probable that Laplace’s concept must be modified 
in one respect; we no longer contemplate a slow gradual shrinkage, but rather 
a contraction by spasms, a star remaining of about the same size through a 
long period of time, after which a fairly rapid contraction occurs, followed by 
another long epoch of unchanging size, another rapid contraction, and so on. 
This jerkiness of contraction is ultimately due to the fact that the atoms 
out of which the stars are built are not continuous structures. The most 
important part of an atom, the positively charged nucleus at its centre, is also 
the smallest. In this, just because of its smallness, the main mass of the atom 
resides. The atom is a very open structure, being rather more so than the solar 
system. The nucleus corresponds to the sun, and around this the other con 
stituents of the atom, the negative electrons, revolve like planets. The revolving 
electrons may form ], 2 , 3 or more rings surrounding the nucleus. At the 
high temperatures which prevail inside the stars the atoms are much broken 
up. As the temperature changes, the size of the atom necessarily changes 
by a whole ring at a time, and these jumps in the sizes of the atoms shew 
themselves in jumps in the sizes of the stars. The radii of atoms which have 
0 , 1 , 2 , 3 ,... rings of electrons revolving round their nuclei are in the proportion 
0 2 : l a : 2 2 : 3 2 : ..., and if all the stars of a given mass are graded according 
to size, we find that they fall into groups in which the radii are in something 
like these same proportions. 
This is of course not the whole story, for the volumes of stars differ sub 
stantially from the aggregate volume of the atoms of which they are formed, 
while theory and observation both shew that the groups of configurations 
corresponding to the different atomic radii remain distinct only in unusually 
massive stars. In stars of moderate mass the distinction becomes blurred, so 
that the various types of configuration merge continuously into one another, 
but we have found that the diameters of stars of large mass reflect quite 
clearly the different possible diameters of the atoms of which they are 
composed. Thus it is possible to say that in one group of stars each atom 
in the main central mass has two rings of electrons left in orbital motion 
around it, in another group of smaller size only one ring of electrons survives, 
while in another group of still smaller size, the “white dwarfs,” nearly all the 
atoms are stripped bare of electrons, and only the positive nuclei are left. 
Thus in a sense the secret of the structure of the atom is written across 
the heavens in the diameters of the stars. For instance, the great disparity 
in size between the white dwarfs and the group of stars of next larger size, 
the “main sequence” stars, provides evidence that the positive nucleus has a 
diameter far smaller than the first ring of electrons surrounding it; we have 
astronomical proof of the “openness of structure” of the atom. 
While a star shrinks, whether continuously or by jerks, its rotation increases, 
and it can run through the whole sequence of configurations just described, 
ending as a binary star.