Page:Encyclopædia Britannica, Ninth Edition, v. 8.djvu/17

Rh HISTORY.] ELECTRICITY formed part of his apparatus, when a tremendous thunder clap burst over the neighbourhood. Richman bent to ob serve the electrometer; while in this position, his head being a foot from the iron rod, Sokolow saw a globe of bluish fire about the size of the fist shoot from the iron rod to the professor s head, with a report like that of a pistol. The shock was fatal ; Richman fell back upon a chest and instantly expired. Sokolow was stupified and benumbed, and the red hot fragments of a metallic wire struck his clothes, and covered them with burnt marks. One of the most diligent labourers in the field of electri cal science was an Englishman, John Canton (Phil. Trans., 1753-54:). Before his time k had been assumed as indis putable that the same kind of electricity was invariably pro duced by the friction of the same electric, that glass, for example, yielded always vitreous, and amber always resin ous electricity. Having roughened a glass tube by grind ing its surface with emery and sheet lead, he found that it possessed vitreous or positive electricity when excited with oiled silk, but resinous electricity when excited with new flannel. He found, in short, that vitreous or resinous electricity might, in certain cases, be developed at will in the same tube, by altering the surfaces of the tube and the exciting rubber. Removing the polish from one half of the tube, he excited the different electricities with the same rubber at a single stroke, and, curiously enough, the rubber was found to move much more easily over the rough than over the polished half. Canton likewise dis covered that glass, arnbsr, sealing-wax, and calcareous spar were all electrified positively when taken out of mercury ; and hence he was led to the important practical discovery that an amalgam of mercury and tin was most efficacious in exciting glass when applied to the surface of the rubber. Canton discovered, and to a certain extent ex plained by the then prevalent theory of &quot; electrical atmo spheres,&quot; the fundamental fact of electrification by induc tion. He also found that the air in a room could be electrified positively or negatively, and might remain thus electrified for a considerable time. Beccaria, a celebrated Italian physicist, kept up the .spirit of electrical discovery in Italy. He showed that water is a very imperfect conductor of electricity, that its conducting power is proportional to its quantity, and that a small quantity of water opposes a powerful resist ance to the passage of electricity. He succeeded in making the electric spark visible in water, by discharging shocks through wires that nearly met in tubes filled with water. In this experiment the tubes, though sometimes eight or ten lines thick, were burst in pieces. Beccaria likewise demonstrated that air adjacent to an electrified body gradually acquired the same electricity, that the electricity of the body is diminished by that of the air, and that the air parts with its electricity very slowly. He con sidered that there was a mutual repulsion between the particles of the electric fluid and those of air, and that in the passage of the former through the latter a temporary vacuum was formed. Beccaria s experiments on atmosphe rical electricity are of the greatest interest to the meteor ologist. For farther account of his work, see his Lettere dell Elettr., 1758; Experimenta, 1772; and letters, &c., in Phil. Trans, about 1770. The science of electricity owes several practical as well as theoretical observations to Robert Symmer (Phil. Trans., about 175 J). In pulling off his stockings in the even ing, he had often remarked that they not only gave a crackling noise, but even emitted sparks in the dark. The electricity was most powerful when a silk and a worsted stocking had been worn on the same leg, and it was best exhibited by putting the hand between the leg and the stockings, and pulling them off together. The one stock ing being then drawn out of the other, they appeared more or less inflated, and exhibited the attractions and repulsions of electrified bodies. Two white silk stockings, or two black ones, when put on the same leg and taken off, gave no electrical indications. When a black and a white stock ing were put on the same leg, and after ten minutes taken off, they were so much inflated when pulled asunder, that each showed the entire shape of the leg, and at the dis tance of a foot and a half they rushed to meet each other. &quot; But what appears most extraordinary is, that when they are separated, and removed at a certain distance from each other, their electricity does not appear to have been in the least impaired by the shock they had in meeting. They are again inflated, again attract and repel, and are as ready to rush together as before. When this experiment is performed with two black stockings in one hand, and two white in the other, it exhibits a very curious spectacle; the repulsion of those of the same colour, and the attraction of those of different colours, throws them into an agitation that is not un- entertaining, and makes them catch each at that of its opposite colour, at a greater distance than one would expect. When allowed to come together, they all unite in one mass. When separated, they resume their former appearance, and admit of the repetition of the experiment as often as you please, till their electricity, gradu ally wasting, stands iu need of being recruited. Symmer likewise found that a Leyden jar could be charged by the stockings either positively or negatively, according as the wire from the neck of the jar was pre sented to the black or the white stocking. When the electricity of the white stocking was thrown into the jar, and then the electricity of the black one, or vice lersa, the jar was not electrified at all. With the electricity of two stockings he charged the jar to such a degree that the shock from it reached both his elbows ; and by means of the electricity of four silk stockings he kindled spirits of wine in a tea-spoon which he held in his hand, and the shock was at the same time felt from the elbows to the breast. Symmer has the merit of having first maintained the theory of two distinct fluids, not independent of each other, as Dufay supposed them to be, but co-existent, and, by counteracting each other, producing all the pheno mena of electricity. He conceived that when a body is said to be positively electrified, it is not simply that it is pos sessed of a larger share of electric matter than in a natural state, nor, when it is said to be negatively electrified, of a less ; but that, in the former case, it is possessed of a larger portion of one kind of electricity, and in the latter, of a larger portion of the other ; while a body, in its natural state, remains unelectrified, because there is an equal amount of the two everywhere within it. Contemporary with Symmer were Delaval, Wilson, Cigna, Kinnersley, Wilcke, and Priestley (for the works of these electricians consult Young). Del aval found that the sides of vessels that were perfect conductors were non conductors, and that animal and vegetable bodies lost their conducting power when reduced to ashes. Wilson con cluded that when two electrics are rubbed together, the harder of the two is generally electrified positively and the other negatively, the electricities always being opposite. Cigna made many curious experiments by using silk ribbands in place of the silk stockings of Symmer. Kin nersley, the friend of Franklin, made some important experiments on the elongation and fusion of iron wires, when a strong charge was passed through them in a state of tension (Phil. Trans., 1763); he also experimented on the disruptive discharge in air. Wilcke brought to light many phenomena respecting the electrification pro duced by the melting of electric substances. The pyro-electricity of minerals, or the faculty possessed by some minerals of becoming electric by heat, and of elec exhibiting negative and positive poles, now began to attrac the notice of philosophers. There is reason to believe that the lyncurium of the ancients, which, according to