ELECTRICITY.

WE E cannot but be somewhat surprised that, among the many attempts which have been made by the philosophers of Britain to explain the wonderful phenomena which are classed under the name of Electricity, no author of eminence, besides the Honourable Mr. Cavendish and Lord Mahon, have availed themselves of their susceptibility of mathemati cal discussion; and our wonder is the greater, because it was by a mathematical view of the subject, in the phenomena of attraction and repulsion, that the celebrated philosopher Franklin was led to the only knowledge of electricity that deserves the name of science; for we had scarcely any leading facts, by which we could class the phenomena, till he published his theory of positive and negative, or plus and minus, electricity. This is founded entirely on the phenomena of attraction and repulsion. These furnish us with all the indications of the presence of the mighty agent, and the marks of its kind, and the measures of its force. Mechanical force accompanies every other appearance; and this accompaniment is regulated in a determinate manner. Many of the effects of electricity are strictly mechanical,

producing local motion in the same manner as magnetism or gravitation produce it. One should have expected that the countrymen of Newton, prompted by his success and his fame, would take to this mode of examination, and would have endeavoured to deduce, from the laws observed in the action of this motive force, an explanation of other wonderful phenomena, which are inseparably connected with those of attraction and repulsion.

But this has not been the case, if we except the labours of the two philosophers above mentioned, and a few very obvious positions which must occur to all the inventors and improvers of electrometers, batteries, and other things of measurable nature.

This view has, however, been taken of the subject by a philosopher of unquestioned merit, Mr. Epinus of the Imperial Academy of St. Petersburgh. This gentleman, struck with the resemblance of the electrical properties of the tourmalin to the properties of a magnet, which have always been considered as the subject of mathematical discussion, fortunately remarked a wonderful similarity in the whole series of electrical and magnetical attractions and repulsions, and set himself seriously to the classification of them. Having done this with great success, and having maturely reflected on Dr. Franklin's happy thought of plus and minus electricity, and his consequent theory of the Leyden phial, he at last hit on a mode of conceiving the whole subject of magnetism and electricity, that bids fair for leading us to a full explanation of all the phenomena; in as far, at least, as it enables us to class them with precision, and to predict what will be the result of any proposed treatinent. He candidly gives it the modest name of a hypothesis.

This was published at St. Petersburgh in 1759, under the title of Theoria Electritatis et Magnetismi, and is unquestionably one of the most ingenious and brilliant performances of this century. It is indeed most surprising that it is so little known in this country. This, we imagine, has

been chiefly owing to the very slight and almost unintelligible account which Dr. Priestley has given of it in his history of electricity; a work which professes to comprehend every thing that has been done by the philosophers of Europe and America for the advancement of this part of natural science, and which indeed contains a great deal of instructive information, and, at the same time, so many loose conjectures and insignificant observations, that the reader reasonably believes that he has let nothing slip that was worthy of notice. We do not pretend to account for the manner in which Dr. Priestley has mentioned this work, so much, and so deservedly celebrated on the Continent. We cannot think that he has read it so as to comprehend it, and imagine, that seeing so much algebraic notation in every page, and being at that time a novice in mathematical learning, he contented himself with a few scattered paragraphs which were free of those embarrassments; and thus could only get a very imperfect notion of the system. The Hon. Mr. Cavendish has done it more justice in the 61st volume of the Philosophical Transactions, and considers his own most excellent dissertation only as an extension and more accurate application of Æpinus's Theory. That we have not an account of this exposition of the Franklinian theory of electricity in our language, is a material want in British literature; and we trust, therefore, that our readers will be highly pleased with having the ingenious discoveries of the great American philosopher put into a form so nearly approaching to a system of demonstrative science.

We propose, therefore, in this place, to give such a brief account of Æpinus's theory of electricity, as will enable the reader to reduce to a very simple and easily remembered law all the phenomena of electricity which have any close dependence on the mechanical effects of this powerful agent of nature; referring for a demonstration of what is purely mathematical to Sir Isaac Newton's Principia, and the Dissertation by Mr. Cavendish already mentioned, except in

such important articles as we think ourselves able to present in a new, and, we hope, a more familiar form. We do not mean, in this place, to give a system of philosophical electricity, nor even to narrate and explain the more remarkable phenomena. We confine ourselves to the phenomena which may be called mechanical, producing measurable motion as their immediate effect; and thus giving us a principle for the mathematical examination of the cause of electrical phenomena. We shall consider the reader as acquainted with the other physical effects of electricity, and shall frequently refer to them for proofs.

Moreover, as our intention is merely to give a synoptical view of this elaborate and copious performance of Mr. Epinus, hoping that it will excite our countrymen to a careful perusal of so valuable a work, we shall omit most of the algebraic investigations contained in it, and present the conclusions in a more familiar, and not less convincing, form. At the same time we will insert the valuable additions made by Mr. Cavendish, and many important particulars not noticed by either of those gentlemen.

HYPOTHESIS OF EPINUS.

1. THE phenomena of electricity are produced by a fluid of peculiar nature, and therefore called the ELECTRIC FLUID, having the following properties:

2. First, Its particles repel each other, with a force decreasing as the distances increase.

3. Second, Its particles attract the particles of some ingredient in all other bodies, with a force decreasing, according to the same law, with an increase of distance; and this attraction is mutual.

4. Third, The electric fluid is dispersed in the pores of other bodies, and moves with various degrees of facility