The negative
ions have much more considerable velocities than the positive ones.
The latter also seem to be of the same size as atoms; and the
first-named must, consequently, be considered as very much smaller,
and probably about a thousand times less.
Thus, for the first time in science, the idea appears that the atom is
not the smallest fraction of matter to be considered. Fragments a
thousand times smaller may exist which possess, however, a negative
charge. These are the electrons, which other considerations will again
bring to our notice.
Sec. 3. HOW IONS ARE PRODUCED
It is very seldom that a gaseous mass does not contain a few ions.
They may have been formed from many causes, for although to give
precision to our studies, and to deal with a well ascertained case, I
mentioned only ionisation by the X rays in the first instance, I ought
not to give the impression that the phenomenon is confined to these
rays. It is, on the contrary, very general, and ionisation is just as
well produced by the cathode rays, by the radiations emitted by
radio-active bodies, by the ultra-violet rays, by heating to a high
temperature, by certain chemical actions, and finally by the impact of
the ions already existing in neutral molecules.
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