ELECTRICITY. 



823 



which actuate the particles of the developed electrici- 

 ties they contain. e. Facts relating to induction. 

 Wherever one of the electricities exists in an active 

 statf, it must repel all the particles of the same elec- 

 tricity in all surrounding bodies, and attract those of 

 the opposite species. Thus the law of induction is 

 seen to be a direct consequence of the hypothesis we 

 are considering. Thus far we have proceeded upon 

 the hypothesis of two distinct electric fluids. It was, 

 however, discovered by Franklin, that it is equally 

 easy to account for all the phenomena, on the sup- 

 position of their resulting from the agency of a single 

 electric fluid. This theory supposes, that the single 

 agent in question, and which we shall call the 

 electric fluid, is highly elastic or repulsive of its own 

 particles, the repulsion taking place with a force 

 varying inversely as the square of the distance ; that 

 its particles attract and are attracted by the particles 

 of all other matter, following the same law of the in- 

 verse square of the distance ; that this fluid is dis- 

 persed through the pores of bodies, and moves 

 through them with various degrees of facility, accor- 

 ding as they are Conductors or non-conductors. 

 Bodies are said to bt u their natural state, with re- 

 gard to this fluid, when the repulsion of the fluid they 

 contain of a particle of fluid at a distance, is exactly 

 balanced by the attraction of the matter in the body 

 for the same particle ; and, under these circum- 

 stances, they exhibit no electrical phenomena. But 

 if subjected to certain operations, as friction, the 

 equilibrium is destroyed, and they acquire more or 

 less than when in their natural state. Whenever they 

 acquire a quantity of fluid greater than in their natu- 

 ral state, they are said to be positively electrified, or 

 to be electrified plus, and present the phenomena 

 ascribed to what was called vitreous electricity. 

 When, on the other hand, there is a quantity less 

 than what is required in order to be in their natural 

 state, they are said to be negatively electrified, or to be 

 electrified minus ; in which case they correspond with 

 the state of resinous electricity. The state of positive 

 electricity, then, consists in a redundance of the 

 lectric fluid, or in matter over-saturated witli this 

 f.uid ; that of negative electricity, in a deficiency of 

 fluid, or in matter under-saturated, or, what may be 

 considered the same thing, in redundant matter. In 

 considering the mutual electrical actions of bodies, 

 the portions in which the matter and the fluid mutu- 

 ally saturate each other, need not be taken into ac- 

 count, since their actions, as we have seen, are per- 

 fectly neutralized ; and we need only attend to those 

 of the redundant fluid and the redundant matter. 

 When a body contains more than its natural propor- 

 tion of electric fluid, the surplus will, by the repul- 

 sive tendency of its particles, overflow and escape, 

 unless prevented by insulation, until the body is re- 

 duced to its neutral state. When under-saturated, the 

 redundant matter will attract fluid from all quarters, 

 from which it can receive, until it is again brought 

 to its natural state. The mutual recession of two 

 positively electrified bodies is a direct consequence 

 of the redundance of the electric fluid contained in 

 each, this fluid being attracted to the matter by its 

 attraction for it in both bodies ; and the fluid in one 

 being repulsive of the fluid in the other, the bodies 

 are necessarily impelled hi the direction of the re- 

 pulsion. In the same manner, the mutual attraction 

 between two bodies, one of which is electrified plus, 

 and the other minus, is the immediate effect of the 

 attraction of the redundant fluid in one for the 

 redundant matter in the other, and vice versa; for 

 this attraction is mutual. The mutual recession of two 

 bodies, negatively electrified, does not appear to be 

 accounted for upon the Franklinian theory. In order 

 to do this, therefore, it has been found necessary to 



append to it the following provision : that particles 

 of simple matter, or bodies nnsaturated with the 

 electric fluid, are mutually repulsive. Without this 

 provision, indeed, we are unable to explain the want 

 of action between two neutral bodies ; for, the re- 

 pulsion of the fluids in both bodies being balanced by 

 the attraction of the fluid in the one for the matter 

 in the other, the remaining attraction of the fluid in 

 the second body for the matter in the first, would be 

 uncompensated by any repulsion ; and the forces 

 would not be held in equilibrium, as we find they 

 really are : The law of electrical induction is an 

 immediate consequence of the Franklinian theory. 

 When a body charged with electricity is presented 

 to a neutral body, the redundant fluid of the former 

 exerts a repulsive action on the fluid in the latter 

 body; and if this happens to be a conductor, 

 it impels a certain portion of that fluid to the 

 remote end of this body, which becomes at that part 

 positively electrified ; while its nearer end, which the 

 same fluid has quitted, is consequently in the state of 

 negative electricity. If the tirst body had been ne- 

 gatively electrified, its unsaturated matter would 

 have exerted an attractive force on the fluid in the 

 second body, and would have drawn it nearer to it- 

 self, producing an accumulation or redundance of 

 fluid at the adjacent end, and a corresponding defi- 

 ciency at the remote end ; that is, the former would 

 have been rendered positive, and the latter negative. 

 All this is exactly conformable to observation. The 

 facts with respect to transference are easily explicable 

 upon this hypothesis, and they arise from the destruc- 

 tion of the equilibrium of forces which confined the 

 fluid to a particular situation or mode of distribution. 

 Indeed, there is no fact which is explained on the 

 hypothesis of two fluids, which is not equally expli- 

 cable on the Franklinian theory ; and the explana- 

 tions by the first are easily converted into those of the 

 second by substituting the expressions of positive and 

 negative for those of vitreous and resinous electricities. 

 The principal advantage of Franklin's system is, its 

 superior simplicity. On the other hand, the pheno- 

 mena of galvanism prove that the two electricities, 

 whatever may be their nature, exert very different 

 chemical agencies, and hence, whichever theory we 

 may choose to adopt, it is necessary, in their chemi- 

 cal history, always to preserve the distinction between 

 them. When viewed, however, as a mere hypothesis, 

 calculated to facilitate our comprehension of the 

 phenomena and of their connexions, it is a matter of 

 indifference which we employ, since they will either 

 of them answer the purpose. For the future, how- 

 ever, we shall more generally employ the language 

 of the Frankliniau theory, on account of its greater 

 convenience. 



III. Electrical Machines Various electric ma- 

 chines have been made; the simplest, though not the 

 most ancient, is the electrophorus. This instrument 

 is represented in fig. 1, plate XXIX. A circular 

 disc, e, is fastened upon a stand, a b. The disc is 

 composed of equal parts of shell lac, resin, and Venice 

 turpentine, melted together, and poured upon a plate 

 of wood or metal. On this there is placed a metallic 

 disc, nearly of the same diameter with the lower one, 

 having two glass handles, d and e. When we wish 

 to draw electricity from this simple instrument, the 

 resinous plate is rubbed with a cat's fur, or a piece 

 of woollen cloth. The metallic plate is then placed 

 upon it, and then lifted by the glass handles, when it 

 will be found to yield an electric spark on presenting 

 a conducting substance to its edge. By bringing the 

 plates again into contact, and again separating them, 

 another spark will be obtained, and this may be con- 

 tinued, and the electricity collected into a Leyden 

 phial, to be afterwards described. The electrophorua 



