The name is absent

The Sizes and Masses of the Stars 87
of the density of the gas, though it will increase rapidly
with the temperature. The rate of recombination of the
ions thus produced with the free electrons, to reconstitute
neutral atoms, will, however, be greatly influenced by the
density. It is obvious that the farther the atoms and elec-
trons are apart, the longer, on the average, they will have
to travel before meeting one another. Hence, though the
atoms will not enter into the ionized state oftener in the gas
of low density, they will remain in it longer, and the per-
centage of all the atoms which are ionized will increase
as the density diminishes. This will favor the absorption
of the enhanced lines at the expense of the lines of the
neutral atom. Now the lines which Adams has picked out,
on the basis of his wide experience, as characteristic of
giant stars, are almost without exception enhanced lines of
a pronounced type. The general character of the physical
process which lies behind his beautiful discovery appears
therefore to be understood. Many details remain obscure
—for example, the prominence in the giant stars of the
hydrogen lines, which belong to the neutral atom. But in
so new a field of work, the presence of such unexplained
phenomena is only a stimulus to further research, and a
comforting reminder that there are still “new worlds to
conquer.”

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