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 rises
into the air, carries with it its portion, however minute that portion may
be, of the earth's electric charge. This small charge distributes itself
over the surface of the aqueous particle, and the vapor rises higher and
higher until it reaches that point above which the air is too rare to
support it.
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