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ELECTRICITY. 195 sible, all figurative language ; and, in the precise and dry phraseology of dynamics, let us speak of the motion of single particles of the electric fluid, deferent fluid, and electric matter. By expansive power, must certainly be meant such a power as that by which air, gases, inflamed gunpowder, steam, and the like, enlarge their bulk, and which is clearly manifested as a mechanical pressure, by bursting vessels, impelling bul lets or pistons, Sic. as well as by the actual enlargement of the bulk of the fluid. We have no other indications of its heing a force; and therefore our notions of its mode of act ing must be derived solely from what we understand of this power in air or the other fluids. Newton’s Principia are our authority for saying, that all that we know of it is, that it acts as a number of corpuscles would act, which repel each other with a force inversely proportional to their distances; this action not extending beyond the adjoining corpuscle, Oot even to the second. We know a good deal of the pro pagation of pressure and progressive motion through such a fluid, when it is confined in a vessel, or system of vessels, of any form, and some few simple circumstances which take place in the clastic undulations which may be excited an d propagated through it. We have but a very indistinct notion of the motions tvhich one mass of such a fluid will P r «duce in another mass, when both are at liberty to ex pand. But we are certain that it will be like the motion °f two masses of air blown or driven against each other. Now these electric fluids, by their expansive powers, must ac t like those others with which we are more familiarly ac fluainted. And here we venture to say, that the ap pearances in electricity are so far from being like these, that cannot imagine any thing more remarkably different, e shall mention but one thing. Every mark that we have or the presence of electric fluid obliges us to grant, that in ttn °'' erc barged hody it is crowded into the external surface, al quantity has little or no relation to the quantity matter in any body but merely to its surface. This is