The Electron is an atom, of disembodied electricity; it occupies an
exceedingly small volume, and its "mass" is entirely electrical. These
electrons are the key to half the mysteries of matter. Electrons in
rapid motion, as we shall see, explain what we mean by an "electric
current," not so long ago regarded as one of the most mysterious
manifestations in nature.
"What a wonder, then, have we here!" says Professor R. K. Duncan. "An
innocent-looking little pinch of salt and yet possessed of special
properties utterly beyond even the fanciful imaginings of men of past
time; for nowhere do we find in the records of thought even the hint of
the possibility of things which we now regard as established fact. This
pinch of salt projects from its surface bodies [i.e. electrons]
possessing the inconceivable velocity of over 100,000 miles a second, a
velocity sufficient to carry them, if unimpeded, five times around the
earth in a second, and possessing with this velocity, masses a thousand
times smaller than the smallest atom known to science. Furthermore,
they are charged with negative electricity; they pass straight through
bodies considered opaque with a sublime indifference to the properties
of the body, with the exception of its mere density; they cause bodies
which they strike to shine out in the dark; they affect a photographic
plate; they render the air a conductor of electricity; they cause clouds
in moist air; they cause chemical action and have a peculiar
physiological action. Who, to-day, shall predict the ultimate service to
humanity of the beta-rays from radium!"
§ 6