ELECTRICITY. 



, so Uiere may be in all bodies 

 some temperature peculiar to each, be- 

 low wliicli its power of conducting elec- 

 tricity may be insensible. 



Conductors of electricity at the usual 

 temperature of the, atmosphere an.-, me- 

 tals, charcoal, water, and very rare air ; 

 non-conductors arc, 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 

 aflbrd 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 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 different and opposite 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- 

 dimdant or positive on the glass; ami 

 deficient, or negative, on the rubber. 



In each h\po;hcsis the matter of all 

 bodies is supposed to attract the electric 

 mutter, and each single fluid to be repul- 

 sive of itself. In the hypothesis of two 

 electric fluids, these are supposed to at- 

 tract each other, and to become neutra- 

 lized by union or combination. Eacli of 

 these hypotheses will agree with most of 

 the phenomena ; and each presents its 

 difficulties : but there are no decisive ex- 

 periments which can entitle either to a 

 preference. We shall use the terms 

 positive and negative in this work, be- 

 cause most commonly adopted. 



The kind of electricity produced by 

 friction on the surface of the non-con- 

 ductor depends, apparently, much 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 smooth glass, 

 and the negative on rough, or unpolish- 

 ed glass; and sealing-wax will 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 

 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. Suppose, 

 for example, an insulated conductor to 

 be positively electrified, or to contain 

 more than the natural or ordinary quan- 

 tity of electricity, this surplus will 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 earth ; and 

 in consequence of the negative state 

 thus produced in this last, there will be 

 an accumulation on the side of the 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 u 

 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 accumulation, 

 which is called the charge, may be made 

 still greater And if the conductors be 



