There is at least one manifestation in nature, and so late as twenty
years ago it seemed to be one of the most mysterious manifestations of
all, which has been in great measure explained by the new discoveries.
Already, at the beginning of this century, we spoke of our "age of
electricity," yet there were few things in nature about which we knew
less. The "electric current" rang our bells, drove our trains, lit our
rooms, but none knew what the current was. There was a vague idea that
it was a sort of fluid that flowed along copper wires as water flows in
a pipe. We now suppose that it is _a rapid movement of electrons from
atom to atom_ in the wire or wherever the current is.
Let us try to grasp the principle of the new view of electricity and see
how it applies to all the varied electrical phenomena in the world about
us. As we saw, the nucleus of an atom of matter consists of positive
electricity which holds together a number of electrons, or charges of
negative electricity.[4] This certainly tells us to some extent what
electricity is, and how it is related to matter, but it leaves us with
the usual difficulty about fundamental realities. But we now know that
electricity, like matter, is atomic in structure; a charge of
electricity is made up of a number of small units or charges of a
definite, constant amount. It has been suggested that the two kinds of
electricity, i.e. positive and negative, are right-handed and
left-handed vortices or whirlpools in ether, or rings in ether, but
there are very serious difficulties, and we leave this to the future.
[4] The words "positive" and "negative" electricity belong to the
days when it was regarded as a fluid. A body overcharged with the
fluid was called positive; an undercharged body was called negative.
A positively-electrified body is now one whose atoms have lost some
of their outlying electrons, so that the positive charge of
electricity predominates. The negatively-electrified body is one
with more than the normal number of electrons.
§ 10