Encyclopaedia Britannica > Volume 8, DIA-England

ELECTRICITY. 619
enome- wrapped round with copper wire. On the 7th June 1753
a and this kite was elevated to the height of 550 feet, by means
Laws. 0f a string 700 feet long, and inclined 45° nearly. A
silk cord three feet and a half long was fixed to its extre¬
mity, and suspended a large stone to govern the motion
of the kite. A tube of white iron, about a foot long and
an inch in diameter, was placed near the junction of the
string and the silk cord, as a conductor, from which the
sparks were to be drawn. From this conductor the spec¬
tators drew sparks with their fingers, keys, canes, and
swords ; and M. Romas having presented his knuckle,
received a shock which struck him in the elbows, shoul¬
ders, breast, knees, and ankles. Seven or eight persons
joined hands, and the shock struck the feet even of the
fifth person. The storm now increased, and black clouds
gathered in the zenith. At the distance of six inches
sparks two inches long were obtained by a discharging
rod. The electricity continuing to increase, flashes of
fire about a foot long, three inches wide, and three lines
in diameter, were frequently received, and the noise of
them was audible at the distance of 500 feet. At this
time he felt the sensation of a spider’s web on his face
when he was five feet from the string. The kite was now
650 feet high, and the wind blowing strong from the east,
when M. Romas saw on the ground, about three feet
from the white-iron tube, three straws dancing up and
down below it. One straw was twelve, another five, and
the third four inches long. The electricity having in¬
creased still more, the longest straw was attracted by the
tube, accompanied with* three loud sounds, which some
compared to the crack of a postilion’s whip, and others to
that of a large pot of earthenware dashed in pieces on a
pavement. This crash was heard even in the centre of
the town, and the accompanying flash had the form of a
spindle eight inches long and four or five lines in diame¬
ter. The long straw followed the string of the kite, and
was seen moving with great rapidity even at the distance
of ninety or a hundred yards, now attracted and now re¬
pelled by the string, each attraction being attended with
long plates of fire and constant explosions. A phos¬
phoric smell was distinctly felt. A permanent cylinder
of light, about three or four inches in diameter, surround¬
ed the string.
M. Romas again raised his kite on the 16th August,
and though the storm was not severe, yet in an hour he
obtained thirty beams of fire, nine or ten feet long, and
about an inch thick, each accompanied by a noise like that
of a pistol. When the glass of his discharging-rod was
two feet long, he was able to conduct beams of fire six or
seven feet long as easily as he had done those of seven or
eight inches, without feeling the slightest shock. On this
occasion the string of the kite was above a thousand feet
long, and the metallic wire which was coiled round it was
continuous throughout.
use of It is obvious, from the preceding facts, that the well-
- rolling known phenomenon of thunder and lightning is entirely an
1‘unden. electrical one, the lightning being the electric spark, and
the thunder the sound which accompanies it prolonged
by successive echoes from among the clouds. That the
clouds are capable of reflecting sound was determined by
direct obsezvation on the sound of cannon, made by Messrs
Arago, Matthieu, and Prony. They observed that in
a perfectly serene sky the explosions of their guns were
always single and sharp, whereas when the sky was over¬
cast, or when a cloud came in sight and covered any con¬
siderable portion of the horizon, the sound of the gun
was attended by a long-continued roll like thunder; and
sometimes a double sound was heard from a single shot.
Sir John Herschel, however, has pointed out another
cause for the rolling of thunder, as well as for its sudden
and capricious bursts and variations of intensity. “ To Phenome-
understand this cause,” says he, “ we must premise that, naand
cceteris paribus, the estimated intensity of a sound will be t ^aws-
proportional to the quantity of it (if we may so express
ourselves) which reaches the ear in a given time. Two
blows, equally loud, at precisely the same distance fi'om
the ear, will sound as one of double the intensity; an hun¬
dred struck in an instant of time will sound as one blow
a hundred times more intense than if they followed in such
slow succession that the ear could appreciate them singly.”
Now let us conceive two equal flashes of lightning,
each four miles long, both beginning at points equi-dis-
tant from the auditoi’, but the one running out in a straight
line directly away from him, the other describing an arc
of a circle having him in its centre. Since the velocity of
electricity is incomparably greater than that of sound,
the thunder may be regarded as originating at one and
the same instant in evezy point of the course of either
flash. But it will reach tlze ear under very different cir¬
cumstances in the two cases. In that of the circular
flash, the sound from every point will az-rive at the same
instant, and affect the ear as a single explosion of stun¬
ning loudness. In that of the rectilinear flash, on the
other hand, the sound from the nearest point will arrive
sooner than from those at a greater distance ; and those
from different points will arrive in succession, occupying
altogether a time equal to that required by sound to run
over four zniles, or about twenty seconds. Thus the same
amount of sound is in the latter case distributed uniform¬
ly over twenty seconds of time, which in the former ar¬
rives at a sinale burst; of course it will have the effect of
a long roar, diminishing zn intenszty as it comes from a
greater and greater distance. If the flash be inclined
in direction, the sound will reach the ear more com¬
pactly (i. e. in shorter time from its commencement), and
proportionally more intense. If (as is almost always the
case) the flash be zigzag, and composed of broken recti¬
linear and curvilinear poz’tions, some concave, sozne con¬
vex to the ear; and if, especially, the principal trunk se¬
parates into many branches, each bz'eaking its own way
through the air, and each becoming a separate souz-ce of
thunder, all the varieties of that awful sound are easily
accounted for.
The distance of the point in the atmosphere where the Distance of
lightning is generated, may be readily computed by mul- thunder,
tiplying 109° by the number of seconds which elapse
between the flash and the first stroke of thunder. The
pi’oduct will give in feet the distance required.
The general phenomenon of thunder and lightning oc¬
curs during the passage of electricity between two clouds
oppositely electrified, or one of which has an inferior
charge of the same kind of electricity; but it appears in
its most appalling forzn when the accumulated electricity
of the clouds descends to the earth, shivering the strong¬
est oak in its passage, rending the thickest wralls, setting
fiz’e to houses, or stacks, or foz-ests, and instantly destzmy-
izzg animal life, when the frail tenement of man or of beast
happens to obstruct its path, or afford to it a more easy
transit. Soznetimes, however, the thunderbolt passes Ascending
from the earth to the clouds, and in this case it is called thunder-
the ascending thunderbolt. The Marquis Mafici was the K) t‘
first who observed this curious phenomenon. He distinct¬
ly saw during a storm the lightning issue fz'ozn the ground
with a loud noise. The Abbe Lioni and M. Seguier ol
Nisznes saw the lightning rise in the form of a flame six
feet high, followed by a loud noise.
One of the most interesting cases of the ascending bolt
has been recorded by John M illiams, Esq. It took place
upon the hills above the village of Great Malvern, on
the 1st of July 1826. A party had taken refuge from the