I hear that the negative electricity of one side of the tourmalin, when heated, is absolutely denied (and all that has been related of it ascribed to prejudice in favor of a system) by some ingenious gentlemen abroad, who profess to have made the experiments on the stone with care and exactness. The experiments have succeeded differently with me; yet I would not call the accuracy of those gentlemen in question. Possibly the tourmalins they have tried were not properly cut; so that the positive and negative powers were obliquely placed, or in some manner whereby their effects were confused, or the negative parts more easily supplied by the positive. Perhaps the lapidaries, who have hitherto cut these stones, had no regard to the situation of the two powers, but chose to make the faces of the stone where they could obtain the greatest breadth, or some other advantage in the form. If any of these stones, in their natural state, can be procured here, I think it would be right to endeavour finding, before they are cut, the two sides that contain the opposite powers, and make the faces there. Possibly, in that case, the effects might be stronger, and more distinct; for, though both these stones, that I have examined, have evidently the two properties, yet, without the full heat given by boiling water, they are somewhat confused; the virtue seems strongest towards one end of the face; and in the middle, or near the other end, scarce discernible; and the negative, I think, always weaker than the positive. I have had the large one new cut, so as to make both sides alike, and find the change of form has made no change of power, but the properties of each side remain the same as I found them before. It is now set in a ring in such a manner as to turn on an axis, that I may conveniently, in making experiments, come at both sides of the stone. The little rim of gold it is set in, has made no alteration in its effects. The warmth of my finger, when I wear it, is sufficient to give it some degree of electricity, so that it is always ready to attract light bodies. The following experiments have satisfied me, that M. Æpinus's account of the positive and negative states of the opposite sides of the heated tourmalin is well founded. I heated the large stone in boiling water. As soon as it was dry, I brought it near a very small cork ball, that was suspended by a silk thread. The ball was attracted by one face of the stone, which I call A, and then repelled. The ball in that state was also repelled by the positively charged wire of a phial, and attracted by the other side of the stone, B. The stone being afresh heated, and the side B brought near the ball, it was first attracted, and presently after repelled, by that side. In this second state it was repelled by the negatively charged wire of a phial. Therefore, if the principles now generally received, relating to positive and negative electricity, are true, the side A of the large stone, when the stone is heated in water, is in a positive state of electricity; and the side B, in a negative state. The same experiments being made with the small stone, stuck by one edge on the end of a small glass tube, with sealing-wax, the same effects are produced. The flat side of the small stone gives the signs of posi tive electricity; the high side gives the signs of negative electricity. Again. I suspended the small stone by a silk thread. I heated it, as it hung, in boiling water. Then I brought the large stone near to the suspended small one; Which immediately turned its flat side to the side B of the large stone, and would cling to it. I turned the ring, so as to present the side of the large stone to the flat side of the small one. The flat side was repelled, and the small stone, turning quick, applied its high side to the side A of the large one. This was precisely what ought to happen, on the supposition, that the flat side of the small stone, when heated in water, is positive, and the high side negative; the side A of the large stone positive, and the side B negative. The effect was apparently the same as would have been produced, if one magnet had been suspended by a thread, and the different poles of another brought alternately near it. I find that the face A of the large stone, being coated with leaf gold (attached by the white of an egg, which will bear dipping in hot water), becomes quicker and stronger in its effect on the cork ball, repelling it the instant it comes in contact; which I suppose to be occasioned by the united force of different parts of the face, collected and acting together through the metal. I am, &c. B. FRANKLIN. FROM E. KINNERSLEY TO BENJAMIN FRANKLIN. Experiments on boiling Water, and Glass heated by boiling Water. - Doctrine of Repulsion in electrized Bodies doubted.- Electricity of the Atmosphere at different Heights. Electrical Horse-race. - Electrical Thermometer. In what Cases the Electrical Fire produces Heat.- Wire lengthened by Electricity. Good Effect of a Rod on the House of Mr. West, of Philadelphia. SIR, Philadelphia, 12 March, 1761. Having lately made the following experiments, I very cheerfully communicate them, in hopes of giving you some degree of pleasure, and exciting you to further explore your favorite, but not quite exhausted subject, electricity. I placed myself on an electric stand, and, being well electrized, threw my hat to an unelectrized person, at a considerable distance, on another stand, and found that the hat carried some of the electricity with it; for, upon going immediately to the person who received it, and holding a flaxen thread near him, I perceived he was electrized sufficiently to attract the thread. I then suspended by silk a broad plate of metal, and electrized some boiling water under it, at about four feet distance, expecting that the vapor, which ascended plentifully to the plate, would, upon the principle of the foregoing experiment, carry up some of the electricity with it; but was at length fully convinced, by several repeated trials, that it left all its share thereof behind. This I know not how to account for; but does it not seem to corroborate your hypothesis, that the vapors of which the clouds are formed, leave their share of electricity behind, in the common stock, and ascend in the negative state? I put boiling water into a coated Florence flask, and found that the heat so enlarged the pores of the glass, that it could not be charged. The electricity passed through as readily, to all appearance, as through metal; the charge of a three-pint bottle went freely through, without injuring the flask in the least. When it became almost cold, I could charge it as usual. Would not this experiment convince the Abbé Nollet of his egregious mistake? mistake? For, while the electricity went fairly through the glass, as he contends it always does, the glass could not be charged at all. I took a slender piece of cedar, about eighteen inches long, fixed a brass cap in the middle, thrust a pin horizontally and at right angles, through each end (the points in contrary directions), and hung it, nicely balanced, like the needle of a compass, on a pin, about six inches long, fixed in the centre of an electric stand. Then, electrizing the stand, I had the pleasure of seeing what I expected; the wooden needle turned round, carrying the pins with their heads foremost. I then electrized the stand negatively, expecting the needle to turn the contrary way, but was extremely disappointed, for it went still the same way as before. When the stand was electrized positively, I suppose that the natural quantity of electricity in the air, being increased on one side by what issued from the points, the needle was attracted by the lesser quantity on the other side. When electrized negatively, I suppose that the natural quantity of electricity in the air was diminished near the points; in consequence whereof, the equilibrium being destroyed, the needle was attracted by the greater quantity on the opposite side. The doctrine of repulsion, in electrized bodies. I |