Abbildungen der Seite
PDF
EPUB

For what had been restored to them, is now taken from them again, flowing back into the prime conductor, and leaving them once more electrized negatively.

Bring the excited tube under the threads, and they will diverge more.

Because more of their natural quantity is driven from them into the prime conductor, and thereby their negative electricity increased.

EXPERIMENT III.

The prime conductor not being electrified, bring the excited tube under the tassel, and the threads will diverge.

Part of their natural quantity is thereby driven out of them into the prime conductor, and they become negatively electrized, and therefore repel each other.

Keeping the tube in the sume place with one hund, attempt to touch the threads with the finger of the other hand, and they will recede from the finger.

Because the finger being plunged into the atmosphere of the glass tube, as well as the threads, part of its natural quantity is driven back through the hand and body by that atmosphere, and the finger becomes, as well as the threads, negatively electrized, and so repels, and is repelled by them. To confirm this, hold a slender, light lock of cotton, two or three inches long, near a prime conductor, that is electrified by a glass globe or tube. You will see the cotton stretch itself out towards the prime conductor. Attempt to touch it with the finger of the other hand, and it will be repelled by the finger. Approach it with a positively charged wire of a bottle, and it will fly to the wire. Bring it near a negatively charged wire of a bottle, it will recede from that wire in the same manner that it

44

VOL. V.

did from the finger; which demonstrates the finger to be negatively electrized, as well as the lock of cotton so situated.

Turkey killed by Electricity. Effect of a Shock on the

Operator in making the Experiment. As Mr. Franklin, in a former letter to Mr. Collinson, mentioned his intending to try the power of a very strong electrical shock upon a turkey, that gentleman accordingly has been so very obliging as to send an account of it, which is to the following purpose.

He made first several experiments on fowls, and found, that two large, thin glass jars gilt, holding each about six gallons, were sufficient, when fully charged, to kill common hens outright; but the turkeys, though thrown into violent convulsions, and then lying as dead for some minutes, would recover in less than a quarter of an hour. However, having added three other such to the former two, though not fully charged, he killed a turkey of about ten pounds weight, and believes that they would have killed a much larger. He conceited, as himself says, that the birds killed in this manner eat uncommonly tender.

In making these experiments, he found, that a man could, without great detriment, bear a much greater shock than he had imagined ; for he inadvertently received the stroke of two of these jars through his arms and body, when they were very near fully charged. It seemed to him a universal blow throughout the body from head to foot, and was followed by a violent, quick trembling in the trunk, which went off gradually, in a few seconds. It was some minutes before he could recollect his thoughts, so as to know what was the matter; for he did not see the flash, though his eye was on the spot of the prime conductor, from whence it struck the back of his hand; nor did he hear the crack, though the by-standers said it was a loud one; nor did he particularly feel the stroke on his hand, though he afterwards found it had raised a swelling there, of the bigness of half a pistol-bullet. His arms and the back of the neck felt somewhat numbed the remainder of the evening, and his breast was sore for å week after, as if it had been bruised. From this experiment may be seen the danger, even under the greatest caution, to the operator, when making these experiments with large jars; for it is not to be doubted, but several of these fully charged would as certainly, by increasing them in proportion to the size, kill a man, as they before did a turkey.

N. B. The original of this letter, which was read at the Royal Society, has been mislaid.*

TO JOHN LINING, AT CHARLESTON, SOUTH CAROLINA.

Differences in the qualities of Glass. Account of Do

mien, an Electrician and Traveller. Conjectures respecting the Pores of Glass. Origin of the Author's Idea of drawing down Lightning. - No satisfactory Hypothesis respecting the Manner in which Clouds become electrified. Six Men knocked down at once by an Electrical Shock. - Reflections on the Spirit of Invention.

Philadelphia, 18 March, 1755. SIR, I send you enclosed a paper containing some new experiments I have made, in pursuance of those by Mr. Canton, that are printed with my last letters. I hope these, with my explanation of them, will afford you some entertainment.*

* See Franklin's letter “ to a Friend in Boston,” p. 255, giving an account of the same accident.

In answer to your several inquiries. The tubes and globes we use here, are chiefly made here. The glass has a greenish cast, but is clear and hard, and, I think, better for electrical experiments than the white glass of London, which is not so hard. There are certainly great differences in glass. A white globe I had made here some years since, would never, by any means, be excited. Two of my friends tried it, as well as myself, without success. At length, putting it on an electric stand, a chain from the prime conductor being in contact with it, I found it had the properties of a nonelectric; for I could draw sparks from any part of it, though it was very clean and dry.

All I know of Domien is, that by his own account he was a native of Transylvania, of Tartar descent, but a priest of the Greek Church; he spoke and wrote Latin very readily and correctly. He set out from his own country with an intention of going round the world, as much as possible by land. He travelled through Germany, France, and Holland, to England. Resided some time at Oxford. From England he came to Maryland; thence went to New England; returned by land to Philadelphia ; and from hence travelled through Maryland, Virginia, and North Carolina to you. He thought it might be of service to him, in his travels, to know something of electricity. I taught him the use of the tube, how to charge the Leyden phial, and some other experiments. He wrote to me from Charleston, that he lived eight hundred miles upon electricity; it had been meat, drink, and clothing to him. His last letter to me was, I think, from Jamaica, desiring me to send the tubes you mention, to meet him at the Havana, from whence he expected to get a passage to La Vera Cruz; designed travelling over land through Mexico to Acapulco; thence to get a passage to Manilla, and so through China, India, Persia, and Turkey, home to his own country; proposing to support himself chiefly by electricity. A strange project ! But he was, as you observe, a very singular character. I was sorry the tubes did not get to the Havana in time for him. If they are still in being, please to send for them, and accept of them. What became of him afterwards, I have never heard. He promised to write to me as often as he could on his journey, and as soon as he should get home after finishing his tour. It is now seven years since he was here. If he is still in New Spain, as you imagine from that loose report, suppose it must be that they confine him there, and prevent his writing ; but I think it more likely that he may be dead.

* See page 330, for the paper here mentioned.

The questions you ask about the pores of glass, I cannot answer, otherwise than that I know nothing of their nature; and suppositions, however ingenious, are often mere mistakes. My hypothesis, that they were smaller near the middle of the glass, too small to admit the passage of electricity, which could pass through the surface till it came near the middle, was certainly wrong. For, soon after I had written that letter, I did, in order to confirm the hypothesis, (which indeed I ought to have done before I wrote it,) make an experiment. I ground away five-sixths of the thickness of the glass, from the side of one of my phials, expecting that, the supposed denser part being so removed, the electric fluid might come through the remainder of the glass, which I had imagined more open; but I found myself mistaken. The bottle charged as well after the

VOL. V.

DD

« ZurückWeiter »