t, in
other words, when work is performed electricity may result. When two
bodies are rubbed together, electricity is produced, so also is it when
two connected metals are immersed in water and one of them is dissolved,
or when one of the junctions of two metals is raised to a higher
temperature than the other junction. I will go further than this, so far,
in fact, as to maintain that there is a reasonable ground for supposing
that every movement, whether it be of the mass or among the constituent
particles, is attended by a change of electrical distribution; and if this
is true, it may easily be conceived that inasmuch as motion is the rule of
the universe, there must be a constant series of electrical changes. Now,
these changes do not all operate in one direction, nor are they all of
similar character, whence it is that not only are there earth currents of
feeble electro-motive force, but that this E.M.F. is constantly varying,
and that, furthermore, electricity of high E.M.F. is to be met with in
various parts of the atmosphere.

With earth currents we have here very little to do. The rotation of the
earth is in itself sufficient to generate small currents, and the fact
that they vary in strength at regular periods of the day and of the year
enforces the suggestion that the sun exerts considerable electrical
influence on the earth. Letting it be granted, however, that the earth is
variously charged, how comes it that the air is also charged, and with
electricity of greater tension than that of the earth itself? It was
pointed out by Sir W. Grove that if the extremities of a piece of platinum
wire be placed in a candle flame, one at the bottom and the other near the
top, an electric current will flow through the wire, indicating the
presence of electricity. If an electrified body be heated, the electricity
escapes more rapidly as the temperature rises. If a vessel of water be
electrified, and the water then converted into steam, the electric charge
will be rapidly dissipated. If a vessel containing water be electrified,
and the water allowed to escape drop by drop, electricity will escape with
each drop, and the vessel will soon be discharged.

We regard it as an established fact that the earth has always a greater or
less charge; whence it is safe to assume that in the process of
evaporation which is going on all over the surface of the globe, more
particularly in equatorial regions, every particle of water, as it r