s they have been, by vivid lightning
discharges of a more or less hurtful nature. The list of disasters
published in _Knowledge_, No. 143, might be very materially augmented were
we to record such damage as has been wrought since that list was compiled.

There is not, I suppose, in the mind of any intelligent man at the present
day a doubt as to the electrical origin of a lightning flash. The
questions to be considered are rather whence comes the electricity, and in
what way is the thunderstorm brought about. In attempting to answer these
questions, sight must not be lost of the fact that the very nature of
electricity is in itself almost sufficient to baffle any effort put forth
to ascertain from lightning, as such, its whence and its whither.

It is possible, however, with the aid of our knowledge of static
electricity, to arrive at hypotheses of a more than chimerical nature. In
the first place, that our sphere is a more or less electrified body is
generally admitted. More than this, it is demonstrated that the different
parts of the earth's surface and its enveloping atmosphere are variously
charged. As a consequence of these varying charges, there is a constant
series of currents flowing through the various parts of the earth, which
show themselves in such telegraph wires as may lie in the direction
followed by the currents. Such currents are known as earth currents, and
present phenomena of a highly interesting nature. But, apart from these
electrical manifestations, there is generally a difference of electrical
condition between the various parts of the earth's surface and those
portions of the atmosphere adjacent to or above them. Inasmuch as air is
one of the very best insulators, this difference of condition (or
potential) in any particular region is in most cases incapable of being
neutralized or equilibrated by an electric flow. Consequently the air
remains more or less continually charged. With these points admitted as
facts, the question arises, Whence this electricity? There have been very
many and various opinions expressed as to the cause of terrestrial
electricity, but far the greater portion of such theories lack fundamental
probability, and indicate causes which cannot be regarded as sufficiently
extensive or operative to produce such tremendous effects as are
occasionally witnessed. I take it that we may safely regard the evolution
of electricity as one of the ways in which force exhibits itself, tha