A NATURAL PHILOSOPHY, CHEMISTRY, AND THE ARTS. JANUARY, 1811. ARTICLE I. Experiments concerning the ELECTRIC MACHINE; showing the Electric Effects of FRICTION between Bodies. By J. A. DE LUC, Esq. F. R. S. THE invention of the electric machine, which has been Invention of the electric machine, within my time, and of which I have followed the progress, was, with respect to the long known effects of friction on amber and other substances, what Sig. Volta's pile has been to the discovery made by Sig. Galvani of the motion produced in the limbs of a recently dead frog by the association of two proper metals: I mean, that, by increasing these effects, a particular fluid has been found to be the cause of both. However, though this fluid has been so long History and discovered by the electric machine, its nature has not yet progress of the been agreed upon among all experimental philosophers. A rapid motion communicated to small globes of different substances, rubbed by the hands, was found to produce certain effects susceptible of being propagated at an unlimited distance through metallic wires, suspended by silk, or supported by glass; and these effects consisted, not only in greater motions of bodies than were produced by the friction of amber, but in strong luminous phenomena. VOL. XXVIII.-No. 126.-JAN. 1811. B The invention. Two kinds of electricity. This new agent, Franklin's theory, exposed to strong objec The greatest effect of friction before observed having been produced by resinous bodies, globes were made of them, especially of sulphur, for electric machines, at the same time as globes of glass, and they both produced the divergence of pairs of balls; but it was soon observed, that the divergence produced by one kind of globe was destroyed by the other kind: whence arose the system of two kinds of electricity, which were supposed to neutralize each other when united, and to be manifested only when separated, producing then their peculiar effects; one of them was called vitreous and the other resinous. This new object of study engrossed the attention of all natural philosophers, not only on its own account, but because of the deficiency of known agents in a great number of natural phenomena; and this interest having been increased, when the analogy between lightning and some of the effects produced by the electric machine was discovered, no wonder that many hasty systems were formed for applying this new, but undetermined agent, to various phe nomena not yet satisfactorily explained, even to the motions of celestial bodies. The idea of two different electricities continued predominant among natural philosophers, till Dr. Franklin explained the difference between the electric phenomena attributed to this double cause by only more or less (plus or minus) of the same fluid: but as this ingenious experimental philosopher assigned the intermediate state between plus and minus to a certain quantity of electric fluid belonging to bodies, his theory, though adopted by the majority of elec tricians, remained subject to insuperable objections under this form; which objections nobody more forcibly urged than Dr. Peart, to whom no solid answer has been made, nor could be made, as long as the theory remained on the sante foundation. Thus many experimental philosophers have retained the idea of two distinct fluids, as producing these two effects which destroy each other: but different hypotheses have been framed on the nature of these fluids, which have been even transformed into certain properties till removed belonging to bodies. However the duration of this variety of systems proceeds only from a want of attention to the by Volta, complete complete solution of all the difficulties, which occurred in the system of plus and minus, given by Sig. Volta, in fixing the real point to which these positive and negative quantities are to be referred, namely, the actual, but different at different times, electric state of the ambient air. According therefore to this system, all the electric phe- Only one elec nomena are produced by one fluid, the modifications of tric fluid. which in terrestrial phenomena deserve the most attentive and assiduous study of all experimental philosophers: but no agreement among them, either on the importance of this study, or on the mode of its pursuit, can be expected, as long as they shall be so far divided in their opinions on the nature of this agent, as to leave a doubt whether it consists of one and the same, or two distinct fluids, or even of some properties of bodies. of triction. Friction between bodies being the only method, hitherte Experiments known, by which can be produced at will the two kinds of on the effects electric signs, I thought that the most direct and sure method of coming to a better knowledge of their meaning was to study them at the origin of the two distinct phenomena; and I undertook a series of experiments on the effects of friction between various kinds of bodies; insulating those which are more or less conductors, and applying electroscopes to both the bodies which exercised friction on each other; in order to observe the modifications thus produced, not only on the nonconducting, but on the conducting bodies. I made these experiments with large apparatusses, by which the reciprocal effects of friction between various bodies were manifested by the motions of pairs of balls; and from them I derived, without exception, the theory which I shall first explain, and then prove by an account of some of the prineipal experiments. I. The electric fluid resides on all terrestrial bodies, every Theory. Conductors particle of air included; being retained upon them by a and noncon mutual attraction, which however differs in degree, accord- ductors. ing to the bodies: some attract the electric fluid only when it comes into contact with them, but then it adheres strongly to the parts which receive it, moving very slowly along the surface of these bodies, which therefore are nonconductors: others receive it at more or less distance, and it is propa tion. gated more or less rapidly along their surface. Glass, though absolutely impenetrable to the electric matter (as I have explained in the preceding paper) permits the electric fluid (i. e. electric matter united with vector) to move with a sensible progress along its surface. Effects of fric- 2. Friction excited between two bodies has no other effect than that of disturbing the natural equilibrium of the electric fluid, which tends always to be produced among all bodies according to its actual (but local, in a certain extent) quantity on them and in the ambient air. If both the bodies, which exercise friction on each other, are good conductors, this disturbance, the equilibrium being constantly restored, is not perceived; but if one has inore disposition than the other to attract the electric fluid thus agitated, with the fuculty of transmitting it to its remote parts; when they are separated, either suddenly, or in general before the equilibrium of the fluid can be restored between them, one is found positive, as having acquired a proportional quantity of electric fluid greater than the ambient air, and the other negative, as having lost that quantity; both being supposed to have previously possessed the same electric state as the ambient air. Negative and positive not properties of different bo. dies, but dif ferent states of 9. The general effect therefore of friction between two bodies is, that one never becomes positive, without the other being made negative (or vice versa). This evident proof, that all the electric phenomena which we are hitherto able to produce at will, namely by friction, proceed from the disturbance of the equilibrium of only one fluid, will be afforded by the experiments, which I shall here relate after another remark. Mr. Cavallo, in his Complete Treatise on Electricity, (3d edit. vol. i, p. 21.) has given a table containing the results of his experiments of this kind, wherein is found, that certain bodies become either positive or negative, according to those the same body. by which they are rubbed. This circumstance had already shown, that negative and positive were not properties belonging to certain bodies, but only different states produced on the sume body by different circumstances, and in particular by the difference of those which exercise friction on it: however, there remained to be known what effect, in the latter latter case, was produced on each of the bodies which exercised that friction. This had been one of my objects in the above mentioned experiments; for which purpose I kept insulated both bodies exercising friction on each other, applying to them electroscopes. It is by experiments thus performed, that I found the general law above expressed; for when any of the bodies, which may be rendered either positive or negative by friction, was brought to one of these states, the body which had exercised it was constantly found in the opposite state: if the former became positive, it had taken some electric fluid from, and if negative, it had yielded sume fluid to, the body which had exercised friction upon it. Such are the effects, which will be seen in the following experiments, contrived, to tween the elec tric machine and pile The small apparatus, which I am going to describe, was Apparatus not at first intended for this purpose; my view in its con- prove the sistruction having been to prove the kind of analogy which milarity be I have established in my former paper, between the electric machine and the electric column, and even the pile, with respect to its electric property; the only difference in this respect between the electric machine and the latter instruments being, that, as in the former the effect is produced by friction, it requires a mechanical process for its continuance; while in the column and in the pile it is produced by only the association of two proper metals. The surest mode of following the course of the electric fluid, when its equilibrium is disturbed, is by the motions of electroscopes; but the immediate comparison which I had in view could not be made with any of the usual electric machines ;.as the gold-leaf being the only electroscope, that can be effected by a pile or column of a moderate size, it would be torn to pieces by the smallest electric machine hitherto used. This made me think of the construction of so small an electric machine, that the gold-leaf electroscope should not be more affected by it than by my largest column; but after the first experiments I was induced to construct this small apparatus so as to be applied to experiments concerning the different effects of friction between different bodies. described. The dimensions of this instrument, as represented in the This apparatus figure Plate I, are, in the parts supposed the nearest to the |