ices that with the aid of this formula,
by merely measuring the actual descent of the top of a vapor cloud,
Professor Thompson was able to find the volume of the drops and thence
the number of particles. The number of particles being known, the
charge of electricity carried by each could be determined, as already
suggested. Experiments were made with air, hydrogen, and carbonic acid,
and it was found that the particles had the same charge in all of these
gases. "A strong argument," says Professor Thompson, "in favor of
the atomic character of electricity." When we add that the charge in
question was found to be the same as the unit charge of an ion in a
liquid, it will be seen that the experiment has other points of interest
and suggestiveness.

Even more interesting in some regards were the results of computation
as to the actual masses of the charged particles in question. Professor
Thompson found that the carrier of a negative charge could have only
about one-thousandth part of the mass of a hydrogen atom, which latter
had been regarded as the smallest mass able to have an independent
existence. Professor Thompson gave the name corpuscle to these units
of negative electricity; they are now more generally termed electrons.
"These corpuscles," he says, "are the same however the electrification
may have risen or wherever they may be found. Negative electricity in a
gas at a low pressure has thus a structure analogous to that of a gas,
the corpuscles taking the place of the molecules. The 'negative electric
fluid,' to use the old notation, resembles the gaseous fluid with a
corpuscular instead of a molecular structure.'" Professor Thompson does
not hesitate to declare that we now "know more about 'electric fluid'
than we know about such fluids as air or water."*3* The results of his
studies lead him, he declares, "to a view of electrification which
has a striking resemblance to that of Franklin's _One Fluid Theory of
Electricity_. Instead of taking, as Franklin did, the electric fluid
to be positive electricity," he says, "we take it to be negative. The
'electric fluid' of Franklin corresponds to an assemblage of corpuscles,
negative electrification being a collection of these corpuscles. The
transference of electrification from one place to another is effected
by the motion of corpuscles from the place where there is a gain of
positive electrification to the place where there is a gain of
negative. A positively electrif