Treatises on electricity, galvanism, magnetism, and electro-magnetism / [Peter Mark Roget].

  • Peter Mark Roget
Date:
1832]
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Licence: Public Domain Mark

Credit: Treatises on electricity, galvanism, magnetism, and electro-magnetism / [Peter Mark Roget]. Source: Wellcome Collection.

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    and charged with any one species of electricity, for other bodies similarly charged, is derived from the repulsive power which the particles of this fluid exert towards those of their own species. Let us suppose a body charged with electricity to be suspended in the air, or otherwise surrounded by a non-con- ducting medium, which allows it to move freely. As long as this body re- mains alone, the outward pressure which the electric fluid exerts against the insulating medium that confines it, will, by the laws of hydrostatics, be equal on all sides; and the body, thus balanced by equal and opposite pres- sures, will have no tendency to move. But if another body, similarly circum- stanced, be brought near it, the repul- sive action between the similar electri- cities contained in these bodies, will diminish the outward pressures of each fluid against the sides of the bodies, (0, c, fig. 8.) which are adjacent to each other; and it will, at the same time, increase the outward pressure on the opposite or remoter sides (a, d.) Both these causes conspire to destroy the equilibrium ; each body is impelled in the direction of the preponderating force, that is, in a direction from the other body ; and an effect, which may be called repulsion, takes place. The very same explanation, it is evident, applies to both kinds of electricity, their properties being in this respect exactly alike. If, on the other hand, a bedy charged with vitreous electricity be presented to one that is charged with resinous electri- city, the attraction of these two fluids will diminish the outward pressure on the remote sides of the bodies, and increase it on the adjacent sides ; hence, the bodies will be urged towards each other, and motions indicative of attraction will result. Thus, in all cases, do the move- ments of the bodies represent the forces themselves which actuate the particles of the developed electricities they con- tain. _(47.) Induction. The law of induc- tion is a direct consequence of the hypo- thesis we are, considering. Wherever one of the electricities exists in an active state, it must repel the particles of the same electricity in all surrounding bo- dies, and attract those of the opposite species: or, in other words, it tends to decompose their united electricities, ac- cumulating the electricity of the oppo- site species towards the nearest side, and impelling that of the same species towards the remote side. The body thus acted upon is no longer neutral, although it contains, on the whole, its natural quantities of both electricities ; but, in consequence of their partial dis- tribution, electrical appearances will be exhibited in its different parts. The further prosecution of this branch of the subject must also be postponed to a subsequent chapter, our present object being merely to point out, in a general way, the coincidence of the fundamental facts with the proposed theory. (48.) Thus far we have proceeded upon the hypothesis of there being two distinct electric fluids, having certain properties in common, but each being characterized by a certain modification of these properties. It is, however, equally possible to account for all the phenomena with the same exactness, on the supposition of their resulting from the agency of a single electric fluid. This simplification of the theory may be considered as the discovery of the im- mortal Franklin, although it had oc- curred at the same period to Dr. Wat- son; for it was Franklin who first pointed out the mode in which it might be successfully applied to explain some of the most remarkable phenomena of the science. Several particular points in his theory, as he originally proposed it, were defective, and were found on strict examination to be at variance with ascertained facts. It is to AZpinus and to Cavendish that we owe the rectifica- tion of these errors: and the theory of Franklin, as thus amended, whatever alterations the future progress of disco- very may oblige us to make in it, will ever remain one of the most beautiful specimens of this kind of reasoning which philosophy has produced. Of this hypothesis we shall now present a brief outline; and point out the mode in which it expiains the phenomena. (49.) We set out, then, with sup- posing that there exists in all bodies a subtile fluid, which we shall call the electric fluid ;—that its particles repel ene another with a force varying in- versely as the square of the distance ;— that they attract the particles of all
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