423 
ELECTRICITY, 
pearance - with his theory of plus and minus eleCtricity, 
but does not exprefs himf'elf well fatisfied with any ex¬ 
planation which had occurred to him. From the begin¬ 
ning, he faw that he could not confider the dream of 
wind as a proof of the efcape of the electric fluid, be- 
eaufe the fame dream is obferved to iflue from a-(harp 
negative point ; which, according to his theory, is not 
dif'perfing, but abforbing it. The Hon. Mr. Cavendiflt 
feems to have given the firft fatisfaCtofy account of this 
phenomenon. To fee it in its full force, the phenomenon 
itfelf muft be carefully obferved. The dream of wind 
is plainly produced by the cfcape of fomeihing from the 
point itfelf, which hurries the air along with it; and this 
alfo draws a great deal of the furrounding air, efpecially 
from behind, in the fame manner as the very (lender 
thread of air from a blow-pipe hurries along with it the 
furrounding air and flame from a con(idei*able furface on 
all fules. It is in this manner that it gathers the whole 
of a large flame into one mafs, and, at lad, into a very 
point. If the fmoke of a little rofin thrown on a live 
coal be made to rife quietly round a point projecting from 
an electrified body, continually fupplied from an electri¬ 
cal machine, the vortices of this fmoke may be obferved 
to curl in from all Tides, along the wire, forming a current 
of which the wire is the axis, and it goes ob' completely 
by the point. But if the wire be made to pafs through 
a cork fixed in the bottom of a wide glafs tube, and if 
its point projeCt not beyond the mouth of the tube, the 
afflux of the air from behind is prevented, and we have 
no dream ; but if the cork be removed, and the wire dill 
occupy the axis of the tube, but without touching the 
Tides, we have the dream very diftinCtly; and fmoke 
which rifes round the far end of the tube is drawn into 
it, and goes off at the point of the wire. Now it is of 
importance to obferve, that whatever prevents the for¬ 
mation of this dream of wind prevents the diffipation of 
eleCtricity from the point. If the point project a quarter 
of an inch beyond the tube, or if the tube be open be¬ 
hind, the dream is drong, and the difflpation lo rapid, 
that even a very good machine is not able to raii'e a 
Henley’s electrometer, banding on a conductor, a very 
few degrees. If the ttibe be Hipped forward, fo that the 
point is jub even with its mouth, the diffipation of elec¬ 
tricity is next to nothing, and does not exceed what might 
be produced by fuch air as can be collected by a fuper- 
ficial point. If the tube be made to advance half an 
inch beyond the point which it furrounds, the diffipation 
becomes infenfible. All thefe faCts put it beyond a 
doubt that the air is the caufe, or, at lead, the occalion 
of- the difflpation, and carries tiie eleCtricity off with it, 
in this manner rendering electrical the whole air of a room. 
It has been demonftrated that two fpheres, connected 
by an infinitely extended, but (lender, conducting canal, 
are in eleCtrical equilibrium, if their furfaces contain 
fluid in the proportion of their diameters. In this cafe, 
the fuperficial denfity of the fluid and its tendency to 
efcape are inverfely as the diameters. Now if, in imagi¬ 
nation, we gradually diminilh the diameter of one of the 
fpheres, the tendency to efcape will increafe in a greater 
proportion titan any that we can name. We know, that 
when the prime conductor of a powerful table-machine 
lias a wire of a few inches in length projecting from its 
end, and terminating in a ball of half an inch in diame¬ 
ter, we cannot eleCtrify it beyond a certain degree ; for 
when arrived at this degree, the eleCtricity flies off in 
fucceffive burds from this ball. Being much more over¬ 
charged than any other part of the body, the air fur¬ 
rounding the ball becomes more overcharged by commu¬ 
nication, and is repelled, and its place fupplied by other 
air, not fo much overcharged, which furrounded the 
other parts of the body, and is prelfed forwards into this 
ipace by the general repullion of the conductor and the 
confining preffure of the attnofphere ; otherwife, being 
alfo overcharged,, it would have no tendency to come to 
Ibis place. Half a turn of the cylinder is fufficient to 
accumulate to a degree fufficient for producing oae of 
thefe expiofions, and we have two of them for every turn 
of the cylinder. A point may be compared to an incom¬ 
parably fmaller ball. The conflipation of the fluid, and 
its tendency to efcape, muft be greater in the fame uiw 
meafurable proportion. This-denfity and mutual re pul- 
lion cannot be diminifhed, and muft even be increafed, 
by the matter of the wire forming a cone, of which the - 
point is the apex ; therefore, if there were no other caufe, 
we muft fee that it is almoft impoffible to confine a col¬ 
lection of particles, mutually repelling, and confiipated, 
as thefe are,, in a fine point. 
But the chief caufe feems to be a.certain chemical- 
union which takes place between the eleftric fluid and a 
correfponding ingredient of the air. In this ftate of con- 
ftipation, almoft completely furrounded by the air, the 
little mafs of fluid muft attract and be attracted with very 
great force, and more readily overcome the force w hich 
keeps the eleCtric fluid attached to the laft feries of par¬ 
ticles of the wire. It unites with tlie air, rendering it 
eleCtric in the higheft degree of redundancy. It is there- , 
fore ftrongly repelled by the mafs of conftipated fluid 
which fucceeds it within the point. Thus is the electri¬ 
fied air continually thrown off, in a ftate of eleChifica- 
tion, that muft rapidly diminilh the eleCtricity of the con¬ 
ductor. Hence the uninterrupted flow, without noife or 
much light, when the point is made very fine. When 
the point is blunt, a little accumulation is neceffary before 
it attains the degree requifite for even this minute explo- 
fion ; but this is foon done, and thefe little, expiofions - 
l'ucceed each other rapidly, accompanied by a fputtering 
noife, and trains of bright fparks. The noife is undoubt¬ 
edly owing to the atoms of the highly eleclrified fluid.. 
Thefe are, in all probability, rarefied of a fudden, in the 
aCt of electrification, and immediately collapfe again ia 
the aCt of chemical union, which caufes a fonorous agi¬ 
tation of the air. This electrified air is thus thrown off, 
and its place is immediately fupplied by air from behind, 
not yet electrified, and therefore ftrongly drawn forward 
to the point, from which they are thrown off in thein 
turn. This rapid expanfion and fubfequent collapfing oF 
the air is verified by the experiments of Mr. Kinnerfly, 
related by Dr. Franklin, and is feen in numberlefs expe¬ 
riments made with other views in later times, and not at¬ 
tended to. Perhaps it is produced by the great heat, 
which accompanies, or is generated in, the transference- 
of eleCtricity, and it is of the fame kind with what occa- 
fions the burfting of (tones, fplitting of trees, exploding 
of metals, &c. by eleCtricity. The expanfion is either 
inconfiderable, or it is fucceifively produced in very fmall 
portions of the fubftance expanded ; for when metai is 
exploded in clofe veffels, or under water, there is but a 
minute portion of gafeous matter produced; and in the 
diffipation by a very fine point, fufficiently great to give 
full employment to a powerful machine, the dream of 
wind is but very faint, and nine-tenths of this has been 
dragged along by the really-eleCtrified thread of wind ia 
the middle. 
From a collation of all the appearances of eleCtricity, 
we muft form the fame conception of the forces which'- 
operate round a point that is negatively eleClrified, not 
difperfing, but drawing in, eleCtric fluid. It is more com¬ 
pletely under-charged titan any other part of a body, and 
attracts the fluid in the furrounding air, and the air in 
which it is retained, with incomparably greater force. 
It therefore deprives the contiguous air of its fluid, then 
repels it, and produces a.dream like the over-charged 
point. 
If a conducting body be brought near to any part of an 
overcharged body, the fronting part of the firft is ren¬ 
dered undercharged ; and this increafes the charge of the 
oppofite part of the overcharged body. It becomes 
more overcharged in that part, and fooner attains that 
degree of conflipation that enables the fluid to quit the 
fuperfieial feries of particles, and to eleCtrify ftrongly the 
i contiguous. 
