VOL. XLIV.^ PHILOSOPHICAL TRANSACTIONS. 40g 



Prop. 1. — In common with light, electricity pervades glass, but suffers no 

 refraction from it; having, from the most exact observations, found its direction 

 to be in right lines, and that through glasses of different forms, included one 

 within the other, and large spaces left between each glass. 



Carol. — This rectilineal direction is observable only as far as the electricity can 

 penetrate through unexcited originally-electrics, and those perfectly dry: nor is 

 it at all material, whether these substances are transparent, as glass, semidia- 

 phanous, as porcelain, or thin cakes of wax; or quite opaque, as thick woollen 

 cloth, as well as woven silk of various colours; it is only necessary that they be 

 originally-electrics. But the case is widely different with regard to non-electrics ; 

 in which the direction, given to the electricity by the excited originally-electric, 

 is altered as soon as it touches the surface of a non-electric, and is propagated 

 with a degree of swiftness scarcely to be measured, in all possible directions, to 

 impregnate the whole non-electric mass in contact with it, or nearly so, however 

 diff^erent in itself, and which must of necessity be terminated by an originally- 

 electric, before the electricity exerts the least attraction; and then this power is 

 observed first at that part of the non-electric the most remote from the originally- 

 electric. Thus, for example, by an excited tube held over it, leaf-gold will be 

 attracted through glass, cloth, &c. held horizontally in the hand of a man 

 standing on the floor, and this attraction is exerted to a considerable distance. 

 On the contrary, the rubbed tube will not attract leaf-gold, or other light bodies, 

 however near, through silver, tin, the thinnest board, paper, or any other non- 

 electric, held in the manner beforementioned. But if you rub the paper over 

 with wax melted, and by that means introduce the originally-electric therein, you 

 observe the electricity acts in right lines, and attracts powerfully. 



Prop. 3. — Electricity, in common with light likewise, when its forces are 

 collected, and a proper direction given to it on a proper object, produces fire. 

 and flame. 



Coral. — The fire of electricity is extremely delicate, and sets on fire, as far as 

 yet experienced, only inflammable vapours. Nor is this flame at all heightened 

 by being superinduced on an iron rod, red-hot with coarser culinary fire, as in a 

 preceding experiment ; nor diminished by being directed on cold water. How- 

 ever, to know if this flame would be affected by a still greater degree of cold; he 

 made an artificial cold, by which the mercury, in a very nice thermometer ad- 

 justed to Fahrenheit's scale, was depressed in about 4 minutes, from 15 degrees 

 above the freezing point to 30 degrees below it: that is, the mercury fell 45 de- 

 grees. From this cold mixture, when electrified, the flashes were as powerful, 

 and the stroke as smart, as from the red-hot iron. This experiment seems to 

 indicate, that the fire of electricity is affected neither by the presence nor absence 

 of other fire. For, as red-liot iron, by Sir Isaac Newton's scale of heat, is fixed 



VOL. IX. 3 G 



