To conceive justly of the nature of thunder and lightning, we have only
to view the effects of a common electrical machine, and its apparatus,
in an apartment. These experiments mimic the great, wonderful and
terrific phenomena of nature. The stream, or spark, from the machine to
the hand, represents the shaft of lightning from the clouds to the
earth; and the snapping noise of the diminutive spark corresponds with
the explosion produced by the lightning, which we call thunder. In what
manner the clouds become electrified, and, in short, what is the nature
of electricity itself, our present range of experiments so little
qualify us to determine, that a century will perhaps elapse before a
philosophical precision can be attained. At present we only know for
certain that the electrical power displays itself merely on the surface
of bodies; and whether it is a fluid =per se=, a vacuum restoring
itself, or whatever its nature may be, the state of experimental
knowledge does not enable us to determine.
The obvious analogy between lightning and electricity, had long been
suspected, and was placed beyond a doubt by Franklin, who was the first
to conceive the practicability of drawing down lightning from the
clouds. Having found by previous experiments, that the electric fluid is
attracted _by points_, he apprehended that lightning might likewise
possess the same quality; although the effects of the latter would in
that case surpass those of the former in an astonishing degree. Flashes
of lightning, he likewise observed, are generally seen crooked and
waving in the air; and the electric spark drawn _from_ an irregular body
at some distance, when it is drawn _by_ an irregular body, or through a
space in which the best conductors are disposed in an irregular manner,
always exhibits the same appearance.
Lightning strikes the highest and most pointed objects in its way, in
preference to others, as high hills, trees, spires, masts, &c.; and all
pointed conductors receive and throw off the electric fluid more readily
than those which are terminated by flat surfaces. Lightning is observed
to take the best and readiest conductor; and this is also the case with
electricity, in the discharge of the Leyden phial; whence Franklin
inferred that, in a thunder-storm, it would be safer for a person to
have his clothes wet than dry. Lightning burns, dissolves metals, rends
some particular bodies, such as the roots and branches of trees, strikes
persons with blindness, destroys animal life, deprives magnets of their
virtue and reverses their poles; and these are well known properties of
electricity. Lightning not only gives polarity to the magnetic needle,
but to all bodies which have any portion of iron in them, as brick, &c.;
and, by observing which way the poles of these bodies lie, the direction
in which the stroke has passed may be known with the utmost certainty.
In order to demonstrate, by actual experiment, the identity of the
electric fluid with the matter of lightning, Franklin contrived to bring
lightning from the heavens by means of an electrical kite, which he
raised on the approach of a thunder-storm; and, with the electricity
thus obtained, charged phials, kindled spirits, and performed all other
electrical experiments, as they are usually exhibited by an excited
globe or tube. This happened in 1752, a month after the French
electricians, pursuing the method which he had proposed, had verified
the same theory; but without any knowledge on his part of what they had
done. On the following year, he further discovered that the air is
sometimes electrified positively, and sometimes negatively; and that in
the course of one thunder-storm, the clouds change from positive to
negative electricity several times. He was not long in perceiving that
this important discovery was capable of being applied to practical use;
and proposed a method, which he soon accomplished, of securing buildings
from being damaged by lightning, by means of conductors, or
lightning-rods, the use of which is now universally known.
From a number of judicious experiments made by him, Signor Beccaria
concluded that the clouds serve as conductors to convey the electric
fluid from those parts of the earth which are overloaded with it, to
those where it is exhausted. The same cause by which a cloud is first
raised, from vapors dispersed in atmosphere, draws to it those which are
already formed, and still continues to form new ones, till the whole
collected mass extends so far as to reach a part of the earth where
there is a deficiency of the electric fluid, and where the electric
matter will discharge itself on the earth. A channel of communication
being thus produced, a fresh supply of electric matter is raised from
the overloaded part, which continues to be conveyed by the medium of the
clouds, till the equilibrium of the fluid is restored between the two
places of the earth. He further observes that as the wind constantly
blows from the place where the thunder-cloud proceeds, the sudden
accumulation of such a prodigious quantity of vapors must displace the
air, and repel it on all sides. Indeed, many observations of the descent
of lightning confirm his theory of the mode of its ascent; for it often
throws before it the parts of conducting bodies, and distributes them
along the resisting medium through which it must force its passage; and
on this principle the longest flashes of lightning seem to be produced,
by its forcing in its way part of the vapors in the air. One of the
chief reasons why the report of these flashes is so much protracted, is
the vast length of the vacuum made by the passage of the electric
matter; for although the air collapses the moment after it has passed,
and the vibration, on which the sound depends, commences at the same
moment, still, when the flash is directed toward the person who hears
the report, the vibrations excited at the nearer end of the track will
reach his ear much sooner than those from the remote end, and the sound
will, without any echo or repercussion, continue till all the vibrations
have successively reached him. The rattling noise of the thunder, which
makes it seem as if it passed through arches or were variously broken,
is probably owing to the sound being excited among clouds hanging over
one another, and the agitated air passing irregularly between them.
Among other precautions pointed out by Franklin, he recommends to those
who happen to be in the fields, at the time of a thunder-storm, to place
themselves within a few yards of a tree, but not quite near it. Signor
Beccaria, however, cautions persons not to depend on a higher, or, in
all cases, a better conductor than their own body; since, according to
his repeated observations, the lightning by no means descends in one
undivided track, but bodies of various kinds conduct their share of it
at the same time, in proportion to their quantity and conducting power.
The late Earl of Stanhope, in his principles of electricity, observes
that damage may be done by lightning, not only by the main stroke and
lateral explosion, but likewise by what he calls _the returning stroke_;
that is, by the sudden violent return of that part of the natural share
of electricity of any conducting body, or any combination of conducting
bodies, which had been gradually expelled from such body or bodies
respectively, by the superinduced elastic electrical pressure of a
thunder-cloud’s electrical atmospheres.
Among the awful phenomena of nature, none have excited more terror than
thunder and lightning. It is recorded of several of the profligate Roman
emperors, who had procured themselves to be deified, that when they
heard the thunder, they tremblingly concealed themselves, acknowledging
a divine power greater than their own; _a Jupiter thundering in the
heavens_.