of that colour, above 5 dwt. in the pair. When the white and the black stocking were warmed at the fire, so as to be prepared for electricity, they usually lost about a 20th part of their weight; so that in the course of the experiments he rated the white at 17 dwt. and the black at 1 oz. The scale, with the silk lines that belonged to it, and the hook, was adjusted precisely to the weight of 1 oz.; and as he commonly measured the strength of cohesion by fixing the hook to the black stocking, and taking hold of the white, he had only to make an allowance of 2 oz. more than the weights put into the scale, so as to take the precise weight the stockings could raise by the power of cohesion.

He measured this power two different ways; the first whilst the one stocking was still within the other; 2dly, when separated, and the one afterwards applied externally to the other. In the first of these cases, it may be thought that an allowance should be made for the friction in pulling the stockings asunder; but that appeared to be very inconsiderable; for when those of the same colour were put one within the other, and inverted, they dropped asunder of themselves; or if there was any entanglement about the heel, a little shaking disengaged and separated them: however, if it should be thought proper, the allowance of an ounce may be made, by deducting so much from the weight respectively found. In the experiments made to measure the force of electrical cohesion, he always found it answerable to the degree of electricity at the time excited. When the stockings have been but weakly electrified, he found them unable to support the weight, the one of the other. When in a more powerful state of electricity, they would raise, respectively, from 1 to 12 ounces and upwards; nay, once he found the cohesion so strong as to move 17 ounces, including the scale and the black stocking.

The greatest weight he had been able to raise by the force of electrical cohesion, has been 17 ounces. Now the white stocking, which weighed but 17 dwt. bore all this weight: in this case therefore it raised, by the strength of its cohesion with the black, nearly 20 times its own weight. And if we consider that the force applied to separate them, acted in a direction parallel to the surfaces, by which they cohered; and that when the surfaces are smooth, a force acting in such direction, has much greater influence in separating bodies, by making them slide gently over one another, than if those bodies were rigid, and the force employed to separate them acted in a direction perpendicular to the cohering surfaces; when we consider this, it will be hard to determine how. great the strength of their cohesion may be.

The force with which the black and the white stocking cohere, is not the only thing remarkable in their junction. The solution of that cohesion, and the different degrees of tenacity, according to different circumstances, afford some curious observations. When the black and the white stocking are in co

hesion with each other,, if another pair, more highly electrified, be separated, and presented to the former still in conjunction, the black to the white, and the white to the black; in that case, the cohesion of the first pair will be dissolved, and each stocking of the second, will carry off that of its opposite colour adhering to it. If the degree of electricity of both pairs be equal, the cohesion of the first pair will be weakened, but not dissolved; and all the 4 will cohere, forming as it were one mass. If the 2d pair be but weakly electrified, the cohesion of the first pair with one another will be but little impaired, and that of the stockings of the 2d with those of the 1st, will be weak in proportion. And lastly, if the 2d pair be not at all electrified, or if, in their stead, any other body not electrified be presented, there will be no effect produced on either hand.

White silk and black, when electrified, not only cohere with each other in the manner shown above, but when in a high degree of electricity, are found, both one and the other, to adhere to bodies of broad and even of polished surfaces, though those bodies be not electrified. This adhesion he discovered accidentally. While he was about some electrical experiments, having accidentally thrown a stocking, that was highly electrified, hastily out of his hand, he was surprized to find it some time after sticking against the paper-hangings of the This led him to make the following experiments.

room.

He presented the white and the black silk, highly electrified, and in cohesion with each other, to the hangings; but no effect was produced. He then sepa rated the black from the white, and presented them singly; in that case each of them readily adhered to the hangings, which they likewise did when flung from a little distance, and continued there for near an hour before they dropped. Having stuck up the black and the white, in the manner above mentioned, he came with another pair of stockings, highly electrified, and applying the white to the black, and the black to the white, he carried them off from the wall, hanging on those that had been applied to them. When the 2d pair were electrified, but to a moderate degree, on applying them as above, the former immediately quitted their hold of the hangings, and dropped to the ground. The same experiments held with the painted boards of the room; and likewise with the looking-glass; to the last of which, both the black, and the white silk, appeared to adhere more tenaciously, than to either of the former.

The late Mons. Du Fay, an ingenious member of the Academy of Sciences at Paris, to whom we owe some valuable: discoveries in electricity, gives an account of something of this nature, in a memoir, presented in the year 1733. Electricity was at that time in its infancy; Mr. Hauksbee had a little before published an account of his experiments; which brought such surprizing appearances of electricity to light, as could not but induce the curious to turn

their eyes on that subject. In the course of those experiments, he had taken notice of something remarkable with regard to colours. Mr. Gray succeeded, and having opened a new path, made still further discoveries in electricity: he likewise, in giving an account of what he had observed, hinted at something curious with regard to colours. But neither of them appear to have come to any determined point in this matter. Mons. Du Fay, who concurred with Mr. Gray, in carrying on electrical discoveries, with a candour and ingenuity that did honour to them both, having entered on an inquiry to determine what sort of bodies were most susceptible of electricity, thought proper, in consequence of what had fallen from Mr. Hauksbee and Mr. Gray, to examine what effect the different colours had in augmenting or diminishing the electricity of different substances.

Accordingly he ranged a number of ribbands, of all the primitive colours, hanging them in the same vertical plane; and to these he applied an excited glass tube, in a horizontal direction. On this he observed, that the black was first attracted; and, as he brought the tube nearer, the white next; and the rest successively, though not always in the same order. He made another experiment, in the same view, with gauzes of different colours, through which. he tried the force of an excited tube, on light bodies placed at a proper distance behind them and from the result he was of opinion, there was something in the influence of colours. But having afterwards tried some experiments with the coloured rays of the sun as refracted by a prism, with flowers of different colours, and with white ribbands rubbed over with differently coloured substances, he began to change his opinion. He likewise had recourse to what he calls a decisive experiment: he dipped his different coloured ribbands in water; and when they were all equally wetted, he applied his tube, and found they were all equally attracted. From this last-mentioned experiment, in particular, he concluded that colours, as colours, had no effect in electricity; but that all was owing to the ingredients of the dye imbibed by the coloured body.

It is not Mr. S.'s purpose here to inquire, whether Mons. Du Fay's conclusion is well or ill founded. Whatever may be the decision of that point, he apprehends the whole of this affair has very little concern with the subject of these papers, and could have been of little use to Mr. S. had he been acquainted' with it before.

PAPER IV. PART I.

Of Two Distinct Powers in Electricity.

With regard to positive and negative electricity, Mr. S.'s notion is, that the operations of electricity do not depend on one single positive power, according to the opinion generally received; but on two distinct, positive, and active

powers, which, by contrasting, and, as it were, counteracting each other, produce the various phenomena of electricity; and that, when a body is said to be positively electrified, it is not simply that it is possessed of a larger share of electric matter than in a natural state; nor, when it is said to be negatively electrified, of a less; but that, in the former case it is possessed of a larger portion of one of those active powers, and in the latter, of a larger portion of the other; while a body, in its natural state, remains unelectrified, from an equal balance of those two powers within it.

All who allow of positive and negative electricity, know, that the Leyden phial, when charged, exhibits electricity in those two states, the one within, the other on the outside; and that when a communication is made between the two, by the means of a non-electric touching the coating, and at the same time approaching the wire, or vice versa, the explosion is produced, and the phial discharged. This reduces the question to a narrow compass; for if, on the discharge of the phial, we meet with proofs not only of a power acting from within to the outside, but also of a power acting at the same instant from the outside to within, then we may fairly conclude, that what is called negative electricity is, in reality, a positive active power; and that electricity, in general, consists not of one alone, but of two distinct, positive powers, acting in contrary directions, and towards each other.

The proof he offers first, is founded on the following experiment. When the phial is electrified but a little, if we touch the coating of it with a finger of one hand, and at the same time approach a finger of the other hand to the wire we shall receive a pretty smart blow on the tip of each of the fingers, the sensation of which reaches no farther: if the phial be electrified a degree higher, we shall feel a stronger blow, reaching to the wrists, but no farther: when again it is electrified to a still higher degree, a severer blow will be received; but will not be felt beyond the elbows: lastly, when the phial is strongly charged, the stroke may be perceived in the wrists and elbows; but the principal shock is felt in the breast, as if a blow from each side met there. This plain and simple experiment seems obviously to suggest to observation, the existence of two distinct powers, acting in contrary directions: and I believe it would be held as a sufficient proof by any who should try the experiment, with a view to determine the question simply from their own perceptions.

But as Mr. S. was sensible that the proof of any important point in philosophy, ought not to depend on the perceptions of this or that particular person, he judged it necessary to have recourse to experiments, the result of which might admit of no ambiguity. The fortunate discovery of M. Muschenbroek and M. Allamand, with the improvements that have since been made on it, puts it in our power to increase electricity to what degree we please. He did not there

fore despair of the means of bringing this matter to a fair decision. He expected, that if an electrical stroke should be made to pass through a solid body, with so much force as to pierce and tear the substance of it, such marks would be left, as might enable us, with certainty, to trace the course of the electrical power in its passage through the body,

Having no apparatus of his own capable of producing such effects, he had recourse to a worthy member of this Society, doctor Franklin, who was possessed of a very good one. He had communicated all his observations to this gentleman as they occurred, and, in return, met with an ingenuity and candour that render him as estimable in private life, as the improvements he has introduced into electricity, and particularly his discovery in relation to thunder and lightning, will render his reputation lasting in the learned world. They differed in opinion with regard to the point in question; yet Mr. S. found Dr. F. ready to give him all the assistance in his power, for bringing the matter to a fair decision. Mr. S. had seen him pierce a quire of paper with a stroke of electricity; and as it had been struck several times before, he desired it might be given him, that he might at leisure examine the effects of the sundry strokes.

When Mr. S. came to do so, he observed, that at every hole which had been made through the quire, the upper and the under leaf (for the quire had been laid in a horizontal position when it was struck) were ragged about the orifice. and those ragged edges pointed mostly outwards from the body of the quire. But, what was more material, when he came to turn over the leaves, he found that the edges of the holes were bent regularly two different ways (and more remarkably so about the middle of the quire,) one part of each hole upwards, and the other part downwards; so that, tracing any particular hole as it traversed the quire, he found on one side the fibres pointed one way, and on the other side the other way; much in such a manner, as if the hole had been made in the quire, by drawing two threads in contrary directions through it. This was not all a piece of paper, covered on one side with Dutch gilding, had been accidentally left between two leaves in the quire, and had been pierced by two different strokes. This exhibited a very remarkable appearance: where each of the strokes had been given, the gold leaf was stripped off, and had left the paper bare for a little space, in an oblong form, rounded at the ends; in which, at the distance of about a quarter of an inch from each other, appeared two points, one of them a little round hole, the other only an indent or impression, such as might have been made by the point of a bodkin. In the leaf which fronted the gilding, two such points likewise appeared, corresponding to those above-mentioned; so that the hole in the one was opposite to the impression in the other, but surrounded with little black or blueish circles. When the hole, which had been struck in the quire, was traced from above down to the gilding