ELECTRICITY. 



sition, so there may be in all bodies 

 some temperature peculiar to eacb, be- 

 low which its power of conducting elec- 

 tricity may be insensible. 



Conductors of electricity at the usual 

 temperature of the atmosphere are, me- 

 tals, charcoal, water, and very rare air ; 

 Bon-conductors are, glass, gems, resins, 

 amber, sulphur, silk, very dry wood oils, 

 dry air of the usual density, and the ba- 

 rometrical vacuum. 



Electricity, or the cause of electric 

 phenomena, is admitted by all philoso- 

 phers 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-conduc- 

 tor, such, for example, as the hand, or a 

 leather cushion, against a tube or cylin- 

 der of glass; for the conditions of which 

 see EXCITATION. The surface of the 

 glass thus becomes electrified, and will 

 afford the electric state by communica- 

 tion to other bodies. An insulated me- 

 tallic conductor, called the prime con- 

 ductor, composes part of the machine 

 used for this purpose. See MACHISTE, 

 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 different and opposite i natures. 

 For, though the cushion and bodies elec- 

 trified by communication from it are ob- 

 served to attract and repel small bodies, 

 and to emit sparks to uninsulated con- 

 ductors, in very nearly the same manner 

 as is done by the cylinder, and such bo- 

 dies 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 

 effects of both ; and bodies, which, hav- 

 ing 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 cushion, that they are, on the con- 

 trary, 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 electri- 

 cities by philosophers, whose attention 

 was directed principally to the non-con- 

 ductor. But Dr. Franklin, who took no- 

 tice of the state of the insulated rubber, 

 adopted the hypothesis of one single 



electric fluid, and supposed it to be re- 

 dundant, or positive, on the glass ; amd 

 deficient, or negative, on the rubber. 



In each hypothesis the matter of all 

 bodies is supposed to attract the eleciric 

 matter, and each single fluid to be repul- 

 sive of itself. In the hypothesis of two 

 electric fluids, these are supposed ijo at- 

 tract each other, and to become neutral- 

 ized by union or combination. Each of 

 these hypotheses will agree with m ost of 

 the phenomena ; and each presents its 

 difficulties : but there are no decisi re ex- 

 periments which can entitle either to a 

 preference. We shall Use' the terms 

 positive and negative in this wo fk, be- 

 cause most commonly adopted. 



The kind of electricity produced by 

 friction on the surface of the ruon-con^ 

 ductor depends, apparently, im ich less 

 on the peculiar nature of the body, than 

 on the mechanical structure of the sur- 

 faces. Thus the same rubber will pro- 

 duce the positive state on smootl glass, 

 and the negative on rough or ui jpolish- 

 ed glass; and sealing-Vax will acquire 

 the positive state, if ' rubbed by the 

 amalgamed leather usually applie< J 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 

 communicate ; and these opposite states 

 diminish each other's apparent power or 

 intensity, so as to admit of a much greater 

 accumulation of electricity than could 

 else have taken place. This may be bet- 

 ter described by stating the fact along 

 with one of the hypotheses. S uppose, 

 for example, an insulated condi ictor to 

 be positively electrified, or to contain 

 more than the natural or ordinal y quan- 

 tity of electricity, this surplus wi 11 repel 

 some of the natural quantity from ano- 

 ther insulated conductor brought" near it, 

 and will drive that surplus out, if a com- 

 munication be made with the eairth ; and 

 in consequence of the negative state 

 thus produced in this last, there will be 

 an accumulation on the side of 'che first 

 conductor nearest to the second, by vir- 

 tue 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 air. If glass 

 be interposed, the spark will be render- 

 ed more difficult, and the accum illation, 

 which is called the charge, may bo made 

 still greater. And if the conductors be 



