But we will confine ourselves here to the facts, and leave the
contending theories to scientific men. It is now pretty generally
accepted that an atom of matter consists of a number of electrons, or
charges of negative electricity, held together by a charge of positive
electricity. It is not disputed that these electrons are in a state of
violent motion or strain, and that therefore a vast energy is locked up
in the atoms of matter. To that we will return later. Here, rather, we
will notice another remarkable discovery which helps us to understand
the nature of matter.
A brilliant young man of science who was killed in the war, Mr. Moseley,
some years ago showed that, when the atoms of different substances are
arranged in order of their weight, _they are also arranged in the order
of increasing complexity of structure_. That is to say, the heavier the
atom, the more electrons it contains. There is a gradual building up of
atoms containing more and more electrons from the lightest atom to the
heaviest. Here it is enough to say that as he took element after
element, from the lightest (hydrogen) to the heaviest (uranium) he found
a strangely regular relation between them. If hydrogen were represented
by the figure one, helium by two, lithium three, and so on up to
uranium, then uranium should have the figure ninety-two. This makes it
probable that there are in nature ninety-two elements--we have found
eighty-seven--and that the number Mr. Moseley found is the number of
electrons in the atom of each element; that is to say, the number is
arranged in order of the atomic numbers of the various elements.
§ 7