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volte ci6 succedere, senza che s' incontri giammai un altera banderuola tanto opportunamente situata tra i limiti della fulminea explosione."

35. But, though the author's explication of these appearances of the vane does not satisfy me, I am not so confident of my own as to propose its being accepted without confirmation by experiment. Those who have strong electric batteries may' try it thus; form a little vane of paper, and spot it on both sides by attaching small pieces of leaf-gold or tinfoil, not exactly opposite to each other; then send the whole force of the battery through the vane, entering at one end of it and going out at the other. If the metal explodes, I imagine it will be found to make holes in the paper, forcing the torn parts out on the sides opposite to the metal. A more expensive but perhaps a more satisfactory experiment would be, to make a new vane as exactly as possible like that in question, in all the particulars of its description, and place it on a tall mast fixed on some hill subject to strokes of lightning, with a better conductor to the earth than the wood of the mast; if this should be struck in the course of a few years, and the same effects appear upon it, it would be still more miraculous to suppose it happened by accident to be exactly situated where those crossing threads of different electricities were afterwards to meet.

36. The perforation of glass bottles when overcharged is, I imagine, a different case, and not explicable by either of these hypotheses; I cannot well suppose the breach to be occasioned by the passage of electricity through it; since a single bottle, though so broken in the discharge, always is found to send round in its usual course the quantity with which it was charged. Then the breach never happens but at the instant of the circuitous discharge, either by-the discharging rod, or in overleaping the borders of the glass. Thus, I have been present when a battery of twenty glasses was discharged by the discharging rod, and produced the same effect in its circuit as if none of the bottles had been pierced; and yet, on examining them, we found no less than twelve of them in that situation. Now, all the bottles of the battery being united by a communication of all the outsides together, and of all the insides together, if one of them had been pierced by a forced passage of the different kinds of electricity to meet each other, before the discharge by the discharging rod, it would not only have prevented the passage of the electricity by the common circuit, but it would have saved all the rest of its fellows, by conducting the whole through its own breach. And it is not easy to conceive that twelve bottles in twenty should be so equally strong as to support the whole strength of their charge, till the circuit of their discharge was opened, and then be so equally weak as to break all together when the weight of that charge was taken off from them by opening the circuits. At some other time I will give you my opinion of this effect, if you desire it .

I have taken the account of this stroke of lightning from an Italian piece, entitled Analisi <f un nuovo Fenome.no del Fulmine, the dedication of which is subscribed Carlo Barletti, delle Scuole Pie, who I suppose is the author. As I do not perfectly understand that language, I may possibly in some things have mistaken that philosopher's meaning. I therefore desire, my dear friend, that you would not permit this to be published, till you have compared and considered it with that original piece, and communicated to me your remarks and corrections. Nor would I in any case have it appear with my name, as perhaps it may occasion disputes, and I have no time to attend to them.

The Leyden Phial, and M. Volta's Experiment*

Paris, 177a

I Thank you for the account you give me of M. Volta's experiment . You judge rightly in supposing, that I have not much time at present to consider philosophical matters; but, as far as I understand it from your description, it is only another form of the Leyden phial . and explicable by the same principles. I must, however, own myself puzzled by one part of your account, viz. "and thus the electric force once excited may be kept alive years together," which is perhaps only a mistake. I have known it indeed to be continued many months in a phial hermetically sealed, and suppose it may be so preserved for ages; but, though one may, by repeatedly touching the knob of a charged bottle with a small insulated plate, like the upper one of the electrophore, draw an incredible number of sparks successively, that is, one after every touch, and those for a while not apparently different in magnitude, yet at length they will become small, and the charge be finally exhausted. But I am in the wrong to give my opinion till I have seen the experiment.

I like much your pasteboard machine, and think it may, in some respects, be preferable to the very large glass ones constructed here. The Due de Chaulnes has one, said, if I remember right, to be five feet in diameter. I saw it tried, but it happened not to be in order.

B. F.

* It is not known to whom this letter was addressed. — Editor.

TO JOHN INGENHOUSZ.

On an Electrical Experiment.

Passy, 16 May, 1783.

I Am glad you have made the experiments you mention, and with success. You will find that the holes are not made by the impulse of the fluid moving in certain directions, but by circumstances of explosion of parts of the matter; and I still think my explanation of the holes in the vane probable, viz. that it was the explosion of tin against parts of the copper plate that were almost in a state of fusion, and therefore easily burst through either on one side or the other, as it happened.* The bursting of the twelve bottles all at once, I take to be owing to small bubbles in the substance of the glass, or grains of sand, into which a quantity of the electric fluid had been forced and compressed while the bottles were charging; and when the pressure was suddenly taken off by discharging the bottles, that confined portion by its elastic force expanding caused the breach. My reasons for thinking, that the charge did not pass by those holes you will find in a former letter ;f and I think you will always find, that the coating within and without is forced both ways by the explosion of these bubbles.

B. Franklin.

* See page 472. \ See page 463.

On- the Shock by the Electric Bottle, and the Density of Glass*

Passy, 14 June, 178a

I received some time since the letter you honored me with, containing your hypothesis for explaining the shock given by the electric bottle, on which you seem to desire my opinion. It is many years since I was engaged in those pleasing studies, and my mind is at present too much occupied with other and more important affairs to permit my returning to them. I cannot therefore examine your ingenious hypothesis with the attention it appears to merit. You will find in a letter of mine to Dr. Lining) dated March 18th, 1755, that I abandoned my hypothesis of the greater density of glass in the middle than near its surfaces, as contributing to produce the effect, because I found the effect to be the same after I had ground that part away.

And I think you might likewise try yours by an easy experiment. Take a plate of lead twelve inches square; cover one of its sides with a coat of bees' wax, about one line thick; upon that apply closely a thin plate of lead eight inches square, so as to leave a margin of two inches all round. Electrify this composition of lead and wax, and try if you can receive a shock from it; if not, you may draw thence a further argument to support your hypothesis, because the wax, though a non-conductor, is not elastic, any more than pure lead. I see you are endowed with a gehius for the study of nature; and I would recommend it to you to employ your time rather in making experiments, than

• It is not known to whom this letter was written. — Editob.

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