<306 
electricity. 
part while it is negative in another, he ad- 
verts to the fall ot great quantities of sand, 
and other light substances, which are often 
carried into the air, and scattered uniformly 
over a large tract of country, when there 
is no wind to effect this phenomenon ; and 
even when there was, they have been car- 
ried against the wind; lie therefore supposes, 
that these light bodies are raised by a large 
quantity of electrical matter issuing from 
the earth. 
This comparatively rare phenomenon, lie 
thinks, exhibits both a perfect image and de- 
monstration of the manner in which the va- 
pours of the atmosphere are raised to form 
thunder clouds. The same electric matter, 
wherever it issues, attracts to it, and carries 
into the higher regions of the air, the watery 
particles dispersed in the atmosphere. The 
electric matter ascends, being solicited bv 
the less resistance it finds there than in the 
common mass of the earth, which at those 
times is generally very dry, and consequent- 
ly highly electric. The uniformity with 
which thunder clouds spread themselves, 
and swell into arches, must be owing to their 
being affected by some cause which, like 
the electric matter, diffuses itself uniformly 
wherever it acts, and to the resistance they 
meet with in ascending through the air. 
The same cause which first raised a cloud 
from vapours dispersed in the atmosphere, 
draws it to those already formed, and con- 
tinues to form new ones, till the whole col- 
lected mass extends so far as to reach a part 
of the earth where there is a deficiency of 
electric fluid ; thither also they will be at- 
tracted, and thus the mass serves as a con- 
ductor. When the clouds are attracted in 
their passage by those parts ot the earth, 
where there is a deficiency of the fluid, those 
detached fragments are formed, and also 
those uniform depending protuberances, 
which are probably the cause of water- 
spouts. 
A wind always blows from the place 
whence a thunder cloud proceeds ; and the 
wind is more or less violent in proportion to 
the sudden appearance of the thunder cloud, 
the rapidity of its expansion, and the velocity 
with which the adscititious clouds join it. 
The sudden condensation of such a prodigi- 
ous quantity of vapour must displace the air, 
and agitate it on all sides. 
In three states of the air, says the author 
above quoted, I could find no electricity in 
it. 1st. In windy weather. 2d. When the 
sky was covered with distinct and black 
clouds, which had a slow motion. 3d. In 
moist weather, not actually raining. 
In rainy weather, without lightning, his 
apparatus was always electrified a little time 
before the rain fell, and during the time of 
rain, but ceased a little before, the rain was 
over. 
The higher his rods reached, or his kites 
flew, the stronger signs they gave of being 
electrified. 
It has been intimated that the clouds are 
sometimes positively, and sometimes nega- 
tively electrified. In the latter case, the 
lightning is supposed, upon the Franklinean 
theory, to proceed from the earth to the 
cloud. The general effects of lightning are 
precisely the same with those of the electric 
shock, only greatly magnified. It may not 
be improper in this place to notice an old 
error, namely, the melting of metals by what 
has been called the cold fusion. The error 
is found to rest upon certain ill-attested re- 
lations of swords being melted in the scab- 
bard, by lightning, and money in a bag, 
without injuring the scabbard or the bag. A 
variety of experiments have been accurately 
made to determine the fact ; the results of 
which have been, that the thin edge of the 
sword, or of the money, might have been 
instantaneously melted, and yet so instanta- 
neously cooled, as neither to affect the scab- 
bard nor the bag. A very sifiall wire will 
instantly melt and instantly cool in the flame 
of a common candle. 
Mr. Kinnesley inclosed a small wire in a 
goose quill filled with loose grains of gun- 
powder, which took lire as readily as if they 
had been touched by a red-hot poker ; tinder 
was kindled when tied to a piece of the same 
wire ; but no such effects could be produced 
with a wire twice as large. Hence it ap- 
pears, as Mr. Kinnesley remarks, that 
though the electrical matter has no sensible 
heat when in a state of rest, it will, in pass- 
ing through bodies, produce heat in them, 
provided they are.proportionably small-. Thus, 
in passing through tire small wire, the par- 
ticles are confined to a narrower passage, 
and, crowding close together, act with a more 
condensed force, and produce sensible heat. 
I he discovery ot Dr. Franklin, which es- 
tablished the identity of lightning with the 
electrical fluid, suggested an invention, for 
which we are indebted to the same philoso- 
pher, for securing buildings from this most 
formidable enemy. The reader will per- 
ceive that we allude to that of metallic con- 
ductors. 
7 1 ' e effects of the electric matter, when it 
strikes a building, and the method of pre- 
venting it, are exemplified by an instrument 
called the thunder-house, representing the 
side of a house, either furnished with a me- 
tallic conductor, or not. A (figure 27) 
is a board about three quarters of an inch 
thick, and shaped like the gable-end of a 
house. T his board is fixed perpendicularly 
upon the bottom board B, upon which the 
perpendicular glass pillar C is also fixed, in 
a hole about eight inches distant from the 
basis of A. A small hole ILMK, about a 
quarter of an inch deep, and nearly one inch 
wide, is made in thq boaid A, and is filled 
with a square piece of wood, nearly of the 
same dimensions. It should be nearly of the 
same dimensions, because it must go so easily 
into the hole that it may drop off by the 
least shaking of the instrument. A wire I K, 
is fastened diagonally to this square piece of 
wood. Another wire L H, of the same 
thickness, having a brass ball II screwed on 
its pointed extremity, is fastened on the 
board A ; so also the wire M N, which is 
shaped in a ring ht N. From the upper ex- 
tremity of the glass pillar C, a crooked wire 
proceeds, having a spring socket F, through 
which a double-knobbed wire slips perpendi- 
cularly, the lower knob G of which falls just 
above the knob H. The glass pillar C must 
not be made very fast in the bottom board ; 
but it must be fixed so that it may be easily 
moved round its own axis, by which means 
the brass ball G may be brought either near- 
er or farther from the ball 11, without touch- 
ing the part E F G. Now, when a square 
piece of wood L M I K (which may repre- 
sent the slmtter of a windo-w or the like) is 
fixed into the hole, so that the wire I K 
stands in the direction L M, then the me- 
tallic communication from H to N is com- 
plete, and the instrument represents a house 
furnished with a proper metallic conductor ; 
but if the square piece of wood L M I Iv is 
fixed so that the wire I K stands in the di- 
rection I K as represented in the figure, 
then the metallic conductor 11 N from the 
top ot the house to its bottom, is interrupted 
at L M : in w hich case the house is not pro- 
perly secured. 
Fix the piece of wood L M I K, so that its 
wire may be as represented in the figure, in 
which case the metallic conductor 11 N is 
discontinued. Let the ball G be fixed at 
about half an inch perpendicular distance 
from the ball Ii : then, by turning the glass 
pillar C, remove the former ball from the 
latter ; by a wire or chain, connect the wire 
E F with the wire Q of the jar P, and let 
another wire or chain, fastened to the hook 
N, touch the outside coating of the jar. 
Connect the wire Q with the prime conduc- 
tor, and charge the jar : then, by turning 
the glass pillar C, 'let the ball G come 
gradually near the ball H, and when they 
are arrived sufficiently near one another, 
you will observe that the jar explodes, and 
the piece of wood LM1K is pushed out 
ot the hole to a considerable distance from 
the thunder-house. Now the ball G in this 
experiment, represents an electrified cloud, 
which, when it is arrived sufficiently near 
the top of the house A, the electricity strikes; 
and as the house is not secured wfth a 
proper conductor, the explosion breaks part 
of it, i. e. knocks off the piece of wood 
IM. 
Repeat the experiment with only this va- 
riation, viz. that this piece of wood I M is 
situated so that the wire 1 K may stand in 
the situation L M, in which case the conduc- 
tor H N is not discontinued ; and you will 
observe, that the explosion will have no ef- 
fect upon the piece* of wood L M, this re- 
maining in the hole unmoved ; which shews 
the usefulness of the metallic conductor. 
Further, unscrew the brass ball H from 
the wire II L, so that this may remain point- 
ed, and with only this difference in the ap- 
paratus, repeat both the above experiments ; 
and you will find the piece of wood L M 
is in neither case moved from its place, nor 
will any explosion be heard. 
The conductor E F G in this experiment 
is supposed to represent a thunder cloud 
discharging its contents on a weathercock, 
or any other metal, at the top of a building ; 
and it may be inferred from this experiment, 
that if there is a connection of metal to con- 
duct the electric fluid down to the earth, 
the building will receive no damage; but 
where the connection is imperfect, it will 
strike from one part to another, and thus 
endanger the whole building. 
Elevated conductors, applied to buildings 
to secure them from lightning, will in this 
manner discharge the electricity from a 
cloud that passes over them, and a greater 
quantity of the discharge will pass through 
a painted conductor than through one which 
terminates with a ball ; but whether the dis- 
charge will be made by a gradual current, or 
by explosion, will depend upon the sudden- 
ness of the discharge, on the nearness and 
