From Ebenezer Kinnersley
Printed in Benjamin Franklin, Supplemental Experiments and Observations on Electricity, Part II. … (London, 1753), pp. 99–101.1 (Yale University Library)
Feb. 3, 1752
I have the following experiments to communicate: I held in one hand a wire, which was fasten’d 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 convey’d 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, sealing wax, 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 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 surprized 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 obtain’d 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, 20 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 fastned 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 can’t 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;2 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.
1. Letter VII in Supplemental Experiments, 1753, and in 1754 and 1760 editions; Letter VIII in 1769 and 1774 editions.
2. BF did so, but the globe was out of repair. See below, p. 269.