ELECTRICITY. 
euliar to each, below which its power of 
conducting electricity may be insensible. 
Conductors of electricity, at the usual 
temperature of the atmosphere, are metals, 
charcoal, water, and very rare air; non- 
conductors are glass, gems, resins, amber, 
sulphur, silk, very dry wood, oils, dry air of 
the usual density, and the barometrical va- 
cuum. 
Electricity, or the cause of electric phe- 
nomena, is admitted by all philosophers to 
consist in some peculiar matter capable of 
being transmitted from place to place 
through conducting bodies. The most 
usual method of producing a strong electric 
state consists in rubbing a conducting body 
against a non-conductor, such, for example, 
as the hand, or a leather cushion, against a 
tube or cylinder of glass; for the conditions 
of which see Excitation. The surface 
of the glass thus becomes electrified, and 
will afford the electric state by communi- 
cation to other bodies. An insulated me- 
tallic conductor, called the prime conductor, 
composes part of the machine used for this 
purpose. See Machine, electric. 
When the rubber is insulated, it is found 
to acquire an electric state as well as the 
cylinder; but the states appear to be of dif- 
ferent and opposite natures. For, though 
the cushion and bodies electrified by com- 
munication from it are observed to attract 
and repel small bodies, and to emit sparks 
to uninsulated conductors, in very nearly 
the same manner as is done by the cylinder, 
and such bodies as have been electrified by 
it ; yet, with regard to each other they are 
so different, that communication between 
the two electricities puts an end to the ef- 
fects of both; and bodies which, having 
been electrified by the cylinder, are in a 
state to be repelled by it, are so far from 
being affected in the same way by the 
cusliion, that they are, on the contrary, 
attracted by it, and vice versa. 
When sealing-wax is rubbed by the hand, 
it acquires upon its surface the opposite 
electricity to that which glass obtains by 
the same treatment; and hence the two 
electricities have been called the vitreous 
and resinous electricities by philosophers 
whose attention was directed principally to 
the non-conductor. But Dr. Franklin, who 
took notice of the state of the insulated 
rubber, adopted the hypothesis of one single 
electric fluid, and supposed it to be redun- 
dant, or positive, on the glass ; and deficient, 
m negative, en tlie rubber. 
In each hypothesis the matter of all 
bodies is supposed to attract the electric 
matter, and each single fluid to be repulsive 
of itself. In the hypothesis of two electric 
fluids, these are supposed to attract each 
other, and to become neutralized by union 
or combination. Each of these hypotheses 
will agree with most of the phenomena ; and 
each presents its difficulties : but there are 
no decisive experiments which can entitle 
either to a preference. We shall use the 
terms positive and negative in this work, 
because most commonly adopted. 
The kind of electricity produced by fric- 
tion on the surface of the non-conductor de- 
pends, apparently, much less on the pecu- 
liar nature of the body, than on the mecha- 
nical structure of the surfaces. Thus the 
same rubber will produce the positive state 
on smooth glass, and the negative on rough, 
or unpolished glass; and sealing-wax w'ill 
acquire the positive state, if rubbed by the 
amalgamed leather usually applied in our 
machines. 
A body electrified in one state tends to 
produce the opposite state in another body, 
if brought near it so as not to communi- 
cate ; and these opposite states diminish 
each other’s apparent power or intensity, 
so as to admit of a much greater accumu- 
lation of electricity than could else have 
taken place. This may be better described 
by stating the fact along with one of the 
hypotheses. Suppose, for example, an in- 
sulated conductor to be positively electri- 
fied, or to contain more than the natural or 
ordinary quantity of electricity, this sur- 
plus will repel some of the natural quantity 
from another insulated conductor brought 
near it, and will drive that surplus out, if a 
communication be made with the earth ; 
and in consequence of the negative state 
thus produced in this last, there will be an 
accumulation on the side of the first con- 
ductor nearest to tlie second, by virtue of 
the diminished repulsion of its electricity. 
The first conductor may, therefore, be made 
to receive still more ; and this effect may be 
carried on until a spark or explosion shall 
take place through the non-conducting aii-. 
If glass be interposed, the spark will be ren- 
dered more difficult, and the accumulation, 
winch is called the charge, may be made 
still greater. And if the conductors be re- 
moved, the charge may still remain at the 
surfaces of the glass ; that is to say, the ac- 
cumulation on the one surface, and the de- 
ficiency on the other, by a want of what 
