Abbildungen der Seite
[ocr errors]

the rising vapors might receive from the air, and retain in the clouds they form; on which I should be glad to have your sentiments. An ingenious friend of mine supposes the land clouds more likely to be electrified than the sea clouds. I send his letter for your perusal, which please to return me.

I have wrote nothing lately on electricity, nor observed any thing new that is material, my time being much taken up with other affairs. Yesterday I discharged four jars through a fine wire, tied up between two strips of glass; the wire was in part melted, and the rest broke into small pieces, from half an inch long, to half a quarter of an inch. My globe raises the electric fire with greater ease, in much greater quantities, by the means of a wire extended from the cushion, to the iron pin of a pump-handle behind my house, which communicates by the pump-spear with the water in the well.

By this post I send to Dr. Perkins, who is curious in that way, some meteorological observations and conjectures, and desire him to communicate them to you, as they may afford you some amusement, and I know you will look over them with a candid eye. By throwing our occasional thoughts on paper, we more readily discover the defects of our opinions, or we digest them better, and find new arguments to support them. This I sometimes practise; but such pieces are fit only to be seen by friends.

I am, with great respect, &c.


.New Experiments. Paradores inferred from them. Difference in the Electricity of a Globe of Glass charged, and a Globe of Sulphur. Difficulty of ascertaining which is positive and which negative.

- [Boston,] 3 February, 1752. SIR, I have the following experiments to communicate. I held in one hand a wire, which was fastened at the other end to the handle of a pump, in order to try whether the stroke from the prime conductor, through my arms, would be any greater than when conveyed only to the surface of the earth, but could discover no difference. I placed the needle of a compass on the point of a long pin, and, holding it in the atmosphere of the prime conductor, at the distance of about three inches, found it to whirl round like the flyers of a jack, with great rapidity. - I suspended with silk a cork ball, about the bigness of a pea, and presented to it rubbed amber, sealingwax, and sulphur, by each of which it was strongly repelled; then I tried rubbed glass and China, and found that each of these would attract it, until it became electrified again, and then it would be repelled as at first; and, while thus repelled by the rubbed glass or China, either of the others when rubbed would attract it. Then I electrified the ball, with the wire of a charged phial, and presented to it rubbed glass (the stopper of a decanter) and a China tea-cup, by which it was as strongly repelled as by the wire; but, when I presented either of the other rubbed electrics, it would be strongly attracted, and, when I electrified it by VOL. V. 35

either of these, till it became repelled, it would be attracted by the wire of the phial, but be repelled by its coating.

These experiments surprised me very much, and have induced me to infer the following paradoxes.

1. If a glass globe be placed at one end of a prime conductor, and a sulphur one at the other end,' both being equally in good order, and in equal motion, not a spark of fire can be obtained from the conductor; but one globe will draw out, as fast as the other gives in.

2. If a phial be suspended on the conductor, with a chain from its coating to the table, and only one of the globes be made use of at a time, twenty turns of the wheel, for instance, will charge it; after which, so many turns of, the other wheel will discharge it; and as many more will charge it again.

3. The globes being both in motion, each having a separate conductor, with a phial suspended on one of them, and the chain of it fastened to the other, the phial will become charged; one globe charging positively, the other negatively.

4. The phial being thus charged, hang it in like manner on the other conductor; set both wheels a going again, and the same number of turns that charged it before will now discharge it; and the same number, repeated, will charge it again.

5. When each globe communicates with the same prime conductor, having a chain hanging from it to the table, one of them, when in motion, (but which I cannot say,) will draw fire up through the cushion, and discharge it through the chain; the other will draw it up through the chain, and discharge it through the cushion.

I should be glad if you would send to my house for


my sulphur globe, and the cushion belonging to it, and make the trial; but must caution you not to use chalk on the cushion; some fine powdered sulphur will do better. If, as I expect, you should find the globes to charge the prime conductor differently, I hope you will be able to discover some method of determining which it is that charges positively. I am, &c. .



Probable Cause of the different Attractions and Repul

sions of the two Electrified Globes mentioned in the preceding Letter.

Philadelphia, 2 March, 1752. SIR, I thank you for the experiments communicated. I sent immediately for your brimstone globe, in order to make the trials you desired, but found it wanted centres, which I have not time now to supply; but, the first leisure, I will get it fitted for use, try the experiments, and acquaint you with the result.

In the mean time I suspect, that the different attractions and repulsions you observed, proceeded rather from the greater or smaller quantities of the fire you obtained from different bodies, than from its being of a different kind, or having a different direction. In haste, I am, &c.


* The Reverend Ebenezer Kinnersley was a professor in the College of Philadelphia. — EDITOR,


Effect of Lightning on Captain Waddeľs Compass, and

on the Dutch Church at New York.


Boston, 2 March, 1752. SIR, I have received your favor of the 24th of January past, enclosing an extract from your letter to Mr. Collinson, and Dr. Colden's letter to yourself, which I have read with a great deal of pleasure, and am much obliged to you for Your extract confirms a-correction Mr. Kinnersley made, a few days ago, of a mistake I was under respecting the polarity given to needles by the electrical fire, “that the end which receives the fire always points north ;” and “that the needle, being situated east and west, will not have a polar direction.” You find, however, the polarity strongest when the needle is shocked lying north and south; weakest when lying east and west; which makes it probable that the communicated magnetism is less, as the needle varies from a north and south situation. As to the needle of Captain Waddel's compass, if its polarity was reversed by the lightning, the effect of lightning and electricity, in regard of that, seems dissimilar; for a magnetic needle in a north and south situation (as the compass needle was), instead of having its power reversed, or even diminished, would have it confirmed or increased by the electric fire. But perhaps the lightning communicated to some nails in the binacle (where the compass is placed) the magnetic virtue, which might disturb the compass.

This I have heard was the case ; if so, the seeming dissimilarity vanishes; but this remarkable circumstance

« ZurückWeiter »