Abbildungen der Seite
PDF
EPUB

In place of taking the hook of the second phial in your hand, run the wire of a third phial, prepared as for the Leyden experiment, through it, and hold this third phial in your hand, the second one hanging to it, by the ends of the hooks run through each other; when the experiment is performed, this third phial receives the fire at D, and will be charged.

D

B

C С

2

1

When this experiment is considered, I think, it must fully prove, that the exterior surface of a charged phial wants electric matter, while the inner surface has an excess of it. One thing more worthy of notice in this experiment is, that I feel no commotion or shock in my arms, though so great a quantity of electric matter passes them instantaneously ; I only feel a pricking in the ends of my fingers. This makes me think the Abbé has mistook, when he says, that there is no difference between the shock felt in performing the Leyden experiment, and the pricking felt on drawing simple sparks, except that of greater to less. In the last experiment, as much electric 'matter went through my arms, as would have given me a very sensible shock, had there been an immediate communication, by my arms, from the hook to the coating of the same phial; because, when it was taken into a third phial, and that phial discharged singly through my arms, it gave me a sensible shock. If these experiments prove, that the

VOL. v.

BB

electric matter does not pass through the entire thickness of the glass, it is a necessary consequence that it must always come out where it entered.

The next thing I meet with is in the Abbé's fifth letter, (p. 88, where he differs from Mr. Franklin, who thinks that the whole power of giving a shock is in the glass itself, and not in the non-electrics in contact with it. The experiments which Mr. Franklin gave to prove this opinion, in his Observations on the Leyden Bottle, (p. 189,) convinced me that he was in the right; and what the Abbé has asserted, in contradiction thereto, has not made me think otherwise.

The Abbé, perceiving, as I suppose, that the experiments, as Mr. Franklin had performed them, must prove his assertion, alters them without giving any reason for it, and makes them in a manner that proves nothing. Why will he have the phial, into which the water is to be decanted from a charged phial, held in a man's hand ? If the power of giving a shock is in the water contained in the phial, it should remain there, though decanted into another phial, since no non-electric body touched it to take that power off. The phial being placed on wax is no objection, for it cannot take the power from the water, if it had any, but it is a necessary means to try the fact; whereas, that phial's being charged when held in a man's hand, only proves, that water will conduct the electric matter. The Abbé owns, (p. 94,) that he had heard this remarked, but says, Why is not a conductor of electricity an electric subject? This is not the question ; Mr. Franklin never said, that water was not an electric subject; he said, that the power of giving a shock was in the glass, and not in the water; and this his experiments fully prove; so fully, that it may appear impertinent to offer any more; yet, as I do not know that the following has been taken notice of by anybody before, my inserting of it in this place may be excused. It is this ; hang a phial, prepared for the Leyden experiment, to the conductor, by its hook, and charge it; which done, remove the communication from the bottom of the phial. Now the conductor shows evident signs of being electrized; for if a thread be tied round it, and its ends left about two inches long, they will extend themselves out like a pair of horns; but, if you touch the conductor, a spark will issue from it, and the threads will fall, nor does the conductor show the least sign of being electrized after this is done. I think, that, by this touch, I have taken out all the charge of electric matter that was in the conductor, the hook of the phial, and water or filings of iron contained in it; which is no more than we see all non-electric bodies will receive; yet the glass of the phial retains its power of giving a shock, as any one will find that pleases to try. This experiment fully evidences, that the water in the phial contains no more electric matter than it would do in an open basin, and has not any of that great quantity which produces the shock, and is only retained by the glass. If, after the spark is drawn from the conductor, you touch the coating of the phial (which all this while is supposed to hang in the air, free from any non-electric body), the threads on the conductor will instantly start up, and show that the conductor is electrized. It receives this electrization from the inner surface of the phial, which, when the outer surface can receive what it wants from the hand applied to it, will give as much as the bodies in contact with it can receive, or, if they be large enough, all that it has of excess. It is diverting to see how the threads will rise and fall by touching the coating and conductor of the phial alternately. May it not be, that, the difference between the charged side of the glass, and the outer or emptied side, being lessened by touching the hook or the conductor, the outer side can receive from the hand which touched it, and, by its receiving, the inner side cannot retain so much; and, for that reason, so much as it cannot contain electrizes the water, or filings, and conductor. For it seems to be a rule, that the one side must be emptied in the same proportion that the other is filled; though this from experiment appears evident, yet it is still a mystery not to be accounted for.

I am, in many places of the Abbé's book, surprised to find, that experiments have succeeded so differently at Paris, from what they did with Mr. Franklin, and as I have always observed them to do. The Abbé, in making experiments to find the difference between the two surfaces of a charged glass, will not have the phial placed on wax; “for,” says he, “ don't you know, that, being placed on a body originally electric, it quickly loses its virtue?” I cannot imagine what should have made the Abbé think so; it certainly is contradictory to the notions commonly received of electrics per se; and by experiment I find it entirely otherwise; for, having several times left a charged phial, for that purpose, standing on wax for hours, I found it to retain as much of its charge as another that stood at the same time on a table. I left one standing on wax from ten o'clock at night till eight the next morning, when I found it to retain a sufficient quantity of its charge to give me a sensible commotion in my arms, though the room in which the phial stood had been swept in that time, which must have raised much dust to facilitate the discharge of the phial.

I find that a cork ball suspended between two bottles, the one fully and the other but little charged, will not play between them, but is driven into a situation

that makes a triangle with the hooks of the phials; though the Abbé has asserted the contrary of this, (p. 101,) in order to account for the playing of a cork ball between the wire thrust into the phial, and one that rises up from its coating. The phial which is least charged must have more electric matter given to it, in proportion to its bulk, than the cork ball receives from the hook of the full phial.

The Abbé says, (p. 103,) “ That a piece of metal leaf, hung to a silk thread and electrized, will be repelled by the bottom of a charged phial held by its hook in the air;" this I find constantly otherwise; it is with me always first attracted and then repelled. It is necessary, in charging the leaf, to be careful that it does not fly off to some non-electric body, and so discharge itself, when you think it is charged; it is difficult to keep it from flying to your own wrist, or to some part of your body.

The Abbé (p. 108) says, “ that it is not impossible, as Mr. Franklin says it is, to charge a phial while there is a communication formed between its coating and its hook.” I have always found it impossible to charge such a phial so as to give a shock; indeed, if it hang on the conductor without a communication from it, you may draw a spark from it, as you may from any body that hangs there; but this is very different from being charged in such a manner as to give a shock. The Abbé, in order to account for the little quantity of electric matter that is to be found in the phial, says, “that it rather follows the metal than the glass, and that it spewed out into the air from the coating of the phial.” I wonder how it comes not to do so too, when it sifts through the glass, and charges the exterior surface, according to the Abbé's system!

The Abbé's objections against Mr. Franklin's two last experiments, I think, have little weight in them; he

42

VOL. V.

BB*

« ZurückWeiter »