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city is more or less powerful. If the electrometer be hung to aprime conductor negatively electrified, i. e. connected with theinsulated rubber of the machine, the cork balls will also repeleach other. If, in tl is state of the repulsion, the prime conductoris touched with some conducting substance, not insulated, thecork balls will immediately come together. But if, instead of theconducting substance, the prime conductor is touched with anelectric, as a stick of sealing-wax, a piece of glass, &c. then thecork balls will continue to repel each other; because the electricfluid cannot be conducted through that electric ; hence we have aneasy method of determining what bodies are conductors and whatelectrics. This electrical repulsion is also shewn by a large downyfeather, which will appear beautifully swelled bv the divergencyof its down.
Attraction and Hepulsion of LtcrtT Bodies. Connectwith the prime conductor, by the hook If, the two parallel brassplates I', G, lig. 11, Plate LX 111. at about three inches from oneanother: and upon the lower plate put any kind of light bodies, asbran, bits of paper, bits of leaf gold. See .; then work the machine,and the light bodies will soon move between the two plates, leap-ing alternately from one to the other with great velocity. If, in-stead of bran or irregular pieces of other matter, small" figures ofmen or other things cut in paper and painted, or rather made of thepith of alder, be put upon the plate, they will generally move inan erect position, but will sometimes leap one upon another, or ex-hibit different postures, so as to afford a pleasing spectacle to anobserving company. When bran or other substances of that kindare made use of, it will be proper to inclose both plates in a glasscylinder, by which the bran will be kept from dispersing and flyingabout the room. The plurnomena of electric attraction and re-pulsion may be exhibited also with a glass tube, or a charged bot-tle, and some of them in a manner more satisfactory than with themachine.
The Electrical Spider, Fig. 12, Plate LX III. represents anelectric jar, having a wire G D E fastened on its outside, which isbended so as to have its knob E as high as the knob A.—B is aspider made of cork, with a few short threads run through it to re-present its legs. It is fastened at the end of a silk thread, proceed-ing from the ceiling of the room, or from any other support, so{hat it may hang mid-way between the two knobs A and L, whenthe jar is not charged. Let the place of the jar upon the table bemarked; then charge the jar, by bringing its knob A in contactwith the prime conductor, and replace it in its marked place. Thespider will now begin to move from knob to knob, and continuethis motion for a considerable time, sometimes for several hours.The inside of the jar being charged positively, the spider is at-tracted by the knob A, which communicates to it a small quantityof electricity; the spider then becoming possessed of the sameelectricity with the knob A, is repelled by it, and runs to the knobE, where it discharges its electricity, and is then attracted by theknob A, and so on. Thus the jar is gradually discharged; andwhen the disc barge is nearly completed, the spider iinishesitsmotion.
The Electrical Jack is an invention of the celebrated Dr.Franklin’s, and turns with considerable force, so that it maysometimes be used for the purposes of a common jack. Asmall upright shaft of wood passes at right angles through a thinround board of about 12 inches diameter, and turns on a sharp pointof iron tixed in the lower end, while a strong wire in the upper end,passing through a small hole in a thin brass plate, keeps the shafttruly vertical. About 30 radii, of equal length, made of window-glass cut into narrow slips, issue horizontally from the circumfe-rence of the board, the ends most distant from the centre beingabout four inches apart. On the end of every one a brass thimbleis tixed. If now the wire of an electrified bottle be brought nearthe circumference of this wheel, it will attract the nearest thimble,and so put the wheel in motion. That thimble, in passing by, re-ceives a spark ; and thereby being electrified, is repelled, and sodriven forwards; while a second, being attracted, approaches thewire, receives a spark, and is driven after the first; and so on, tillthe wheel has gone once round ; when the thimbles before elec-trified approaching the wire, instead of being attracted, as theywere at first, are repelled, and the motion presently ceases. Butif another bottle which had been charged through the coaling, orotherwise negatively electrified, is placed near the same wheel itswire will attract the thimble repelled by the first, and thereby
double the force l at carries the wheel round. The wheel there-fore moves very swiftly, turning .12 or 15 times in a minute, andwith such force, that a large fowl spitted on the upper shaft may lieroasted by it.
The Self-Moving Wheel. This appears more surprising,than the last experiment, though constructed upon the same prin-ciples. It is made of a thin round plate of window glass 17 inchesin diameter, well gilt on both sides, all but two inches next theedge. Two small hemispheres of wood arc then fixed v. ith cementto the middle of the upper and under sides, centrally opposite ;and in each of them a strong thick wire eight or ten inches long,which together make the axis of the wheel. It turns horizontallyon a point at the. lower end of its axis, which reds on a bit of bne-scemented within a glass salt-cellar. The upper end of its axispasses through a hole in a thin brass plate, cemented to a long andstrong piece of glass; which keeps it six or eight inches distantfrom any non-elcctric, and has a small ball of wax or metal on itstop to keep in the lire. In a circle on the table which supportsthe wheel, are fixed 12 small pillars of glass, at about 11 inches dis-tance, with a thimble on the top of each. On the edge of teewheel is a small leaden bullet, communicating by a wire with thegilding of the upper surface of the wheel; and about six inchesfrom it is another bullet communicating in like manner with theunder surface. When the wheel is to be charged by the uppersurface, a communication must be made from the under surface tothe table. As soon as it is well charged, it begins to move. Thebullet nearest to a pillar moves towards the thimble on that pillar:and, passing by, electrifies it, and is then repelled from it. Thesucceeding bullet, which communicates with the other surface ofthe glass, more strongly' attracts that thimble on account of itsbeing electrified before by the other bullet; and thus the wheel in-creases its motion, till the resistance of the air regulates it. it willgo half an hour; and make, one minute with another, 20 turns in aminute, which is 600 turns in the whole; the bullet in the uppersurface giving in each turn 12 sparks to the thimbles, making in all2500 sparks; while the same quantity of fire is thought to be re-ceived by the under bullet, f he whole space moved over bythese bullets in the mean time is 2500 feet. If, instead of two bul-lets, you put eight, four communicating with the upper, and fourwith the under surface, the force and swiftness will be greatly in-creased, and the wheel will make about 50 turns in a minute ; butthen it will not continue moving so long. These wheels may beapplied to the ringing of chimes,and the moving of small orreries, &c.
The Electrified Beli.s, I-’ig. 13, Plate LX1II. representsan instrument having three bells, which are made to ring by elec-tric attraction and repulsion. R is a brass rod, furnished with aring, A, of the same metal, by which it is suspended from anotherrod fixed in the prime conductor. The outer bell? G and E aresuspended by brass chains; but the middle bell D and the twosmall brass clappers G and H are suspended by silk threads. Fromthe concave under part of the bell D a chain proceeds, which fallsupon the table, and bus a silk thread F, at its extremity. Whenthis apparatus is hung to the conductor by the ling A, and thecylinder of the machine gently turned, the clappers will fly frombell to bell with a rapid motion, and the bells will ring as long asthey are kept electrified. The two bells G and E being suspendedby brass chains are first electrified : hence they attract the clap-pers, communicate to them a little electricity, and repel them tothe unelectrified bell I) ; upon which the clappers deposit theirelectricity, and move again to the bells CE, from uhicli they ac-quire more, and so on. If, by holding the silk thread F, thechain of the middle bell be raised from the table, the bells afterringing a little while will stop ; because the bell D will luive noopportunity of conveying the electricity it receives from the dap-pers to the ground, being insulated by the silk thread. In thedark, sparks will be seen between the clappers and bells. Fig.14 represents a set of bells more elegantly mounted, and whichproduce a better sound. In these the knob u must communicatewith the conductor when the apparatus is made use of. Fig. 15represents a set of eight bells otherwise constructed. The clapperh is here suspended by a silken thread from the fly a b c d: theaxis of the fly rests in a small hole on the top of a glass piMar ; andits upper part moves freely in, and is confined by a hole in the liras*arm g. To make use of the bells these must he applied to thecylindcrof the machine, or at least brought very near itwlien the con-14 dueler