A letter from Paris concerning some new electrical experiments made there / [John Turberville Needham].

  • John Needham
Date:
1746
Catalogue details

Licence: Public Domain Mark

Credit: A letter from Paris concerning some new electrical experiments made there / [John Turberville Needham]. Source: Wellcome Collection.

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    feeling, than as a continual blaft of wind. —tfhe third exp. is performed with a fquare bar of iron, about four feet in length, and half an inch in thicknefs to one extremity of which is adapted, by the help of a fcrew, another piece of iron beat flat, like the end of one of the legs of a pair of tongs. This flat piece of iron being fcrewed in, the bar is placed parallel to the horizon upon a wooden ftand, and the ftand within the *rea of the drawer or box, upon the pitch, refin, and bees wax, as above. The extremity of the bar, oppofite to that, which carries the flat piece of iron, is covered with three or four folds of linen, to prevent any damage that might happen to the glafs fphe- roid, in hitting againft it by accident, while it revolves round its axis ; and the fame extremity is moreover, for further fecurity, placed at the difiance of about one-fourth of an inch from the glafs itfelf, the effeCt being the fame in every refpeCt, as if in contaCt. The operator then orders the bar to be eleCtrified by repeated revolutions of the glafs fpheroid, as above ; and places one finger upon the middle of the bar, to prevent the communication of the electricity from one end to the other, till he has covered the flat piece of iron with as much faw-duft as it will carry. Some other of the company, in the mean while, takes up on the point of a knife likewife, a quantity of faw- duft, and holds it under the flat piece of iron, at about an inch diftance. The efleCt is, that when the operator takes off his finger, the fpheroid ftill continuing to revolve, the faw-dufl; above is all repelled and blown off, and that under attracted upwards. If, inftead of faw-dufl, you place upon the flat piece of iron a fmall fquare tin-box filled with water, or any other veffel made of a matter non-eleCtric per fe, particularly metalline, and endeavour to draw off the water by a capillary fiphon, the water, in that cafe, will fall drop by drop, as ufually ; but the inflant the bar is electrified, it runs in one continual ftream ; which, if the chamber be darkened, will alfo appear lumi¬ nous. This play of the water may again be flopped at pleafure, by the ap¬ plication of one finger to the bar, as above. If the flat piece of iron be un- fcrewed and removed, the eleClricity runs out at the extremity of the bar, to the eyes, in the appearance of a blewifh flame; to the fmell, like fumes of phofphorus *, and, to the feeling, like a blaft of wind; as in the experiment of the fword.—But the moft furprifing of all is, experiment the fourthy which is that of Mufchenbroeck, improved by monfieur le Monnier ; a mufquet-barrel open at both ends, is fufpended parallel to the horizon, by filken threads within reach. At the breech end, about three inches from the extremity, is hung, by a ring of iron worked into the barrel itfelf^ a fmall iron chain about half a foot in length. A glafs phial, refembling in fize and fhape a common vinegar crewet, is then prepared, full of water and well corked, with an iron wire running through the cork almoft to the bottom, and emerging Tome two or three inches above it, out of the top of the phial. The head of this wire is bent, to catch in the loweft link of the chain \ and is to be there fufpended, when it has been eleCtrified. From the mouth of the barrel, which is pointed in a line parallel to the equatorial plane of the revolving Ipheroid, comes a long iron wire, inferted into the barrel itfelf, as far as A 2 ' one-
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