There is general agreement amongst all chemists, physicists, and
mathematicians upon the conclusions which we have so far given. We know
that the atoms of matter are constantly--either spontaneously or under
stimulation--giving off electrons, or breaking up into electrons; and
they therefore contain electrons. Thus we have now complete proof of the
independent existence of atoms and also of electrons.
When, however, the man of science tries to tell us _how_ electrons
compose atoms, he passes from facts to speculation, and very difficult
speculation. Take the letter "o" as it is printed on this page. In a
little bubble of hydrogen gas no larger than that letter there are
_trillions_ of atoms; and they are not packed together, but are
circulating as freely as dancers in a ball-room. We are asking the
physicist to take one of these minute atoms and tell us how the still
smaller electrons are arranged in it. Naturally he can only make mental
pictures, guesses or hypotheses, which he tries to fit to the facts, and
discards when they will _not_ fit.
At present, after nearly twenty years of critical discussion, there are
two chief theories of the structure of the atom. At first Sir J. J.
Thomson imagined the electrons circulating in shells (like the layers of
an onion) round the nucleus of the atom. This did not suit, and Sir E.
Rutherford and others worked out a theory that the electrons circulated
round a nucleus rather like the planets of our solar system revolving
round the central sun. Is there a nucleus, then, round which the
electrons revolve? The electron, as we saw, is a disembodied atom of
electricity; we should say, of "negative" electricity. Let us picture
these electrons all moving round in orbits with great velocity. Now it
is suggested that there is a nucleus of "positive" electricity
attracting or pulling the revolving electrons to it, and so forming an
equilibrium, otherwise the electrons would fly off in all directions.
This nucleus has been recently named the proton. We have thus two
electricities in the atom: the positive = the nucleus; the negative =
the electron. Of recent years Dr. Langmuir has put out a theory that the
electrons do not _revolve round_ the nucleus, but remain in a state of
violent agitation of some sort at fixed distances from the nucleus.
[Illustration: PROFESSOR SIR J. J. THOMSON
Experimental discoverer of the electronic constitution of matter, in the
Cavendish Physical Laboratory, Cambridge. A great investigator, noted
for the imaginative range of his hypotheses and his fertility in
experimental devices.]
[Illustration: _From the Smithsonian Report_, 1915.