ELECTRICITY. 



n m ":i 



electro- 

 meter. 



Carallo'i 

 electro- 

 meters. 



PLATE 



rrxi.ix. 

 hi* 8. 



, > of tinfoil 6, t, and thus convey the electricity to 

 ^ the ground. 



M r C'avallo has proposed to improve this electrom 

 by sticking two small piece* of gilt paper to tin- end* of 

 the gold leave*. 



4. tficholfon't Improvement on Bennei's Electrometer. 



As tlie divergency of the gold leaves in the preceding 

 instrument is increased by the stripes of tinfoil b, c, it 

 might happen that the electricity was so weak that it 

 could only be rendered sensible by having tin- stripes 

 b, c brought very near to the gold leaves. With this 

 view, Mr Nicholson constructed an apparatus, in which 

 he substituted two flat radii of brass in room of the tin- 

 foil, and, by means of a micrometer screw .placed nt 

 the foot of tlie glass cylinder, he was able to open and 

 shut the two radii of brass, so that their extrein it ie< 

 could be brought within any distance of the gold leaves. 

 The divergency of the brass radii afford a kind of mea- 

 sure of the intensity of the electricity. A drawing and 

 description of this improved instrument may be seen in 

 Nicholson's Journal, September 1797. 



5. C'avullo's Electrometers. 



The electrometers constructed and used by Mr Cavallo 

 are represented in Plate CCXLIX. Figs 8 and 9. Fig. 

 8. is his pocket electrometer, shewn in its inner case nt 

 A, and in a state of action at B. The inner case or handle 

 is made of glass, and is about three inches long, and -^ 

 of an inch wide, half of it being covered with sealing- 

 wax. To the open end of the tube is fitted a cork 

 which tapers at both ends, so that any end of it will 

 suit tlie end of the tube. Two small cones of the pith of 

 elder are then suspended to two linen threads attached 

 to one end of the cork. When the electrometer is to 

 be used, the end of the cork opposite to the threads 

 must be put into the tube, and the tube will form the 

 insulated handle of the electrometer, as shewn at B. 

 The case of this electrometer, shewn at C, contains a 

 piece of amber at one end, for electrifying the electro- 

 meter negatively, and at the other end a piece of ivory 

 insulated upon a piece of amber, for giving positive 

 electricity when rubbed by woollen cloth. 



Another electrometer of Cavallo's is represented in 

 Fig. 9. at A, which does not differ very essentially from 

 Beimel's, having small conical pieces of the pith of el- 

 der, instead of gold leaves. These balls are suspended 

 by two silver wires, which hang parallel to one another 

 when the balls are at rest. The wires are shaped 

 like rings at the top, and hang very loosely in holes, in 

 a piece of ivory H. The cap of the electrometer has a 

 particular construction, which will be seen at B. 



6. Saussitre's Electrometer. 



This electrometer is represented in Fig. 10. of Plate 

 CCXLIX. and has a general resemblance to that of 

 Cavallo's. The balls are round, and made of the pith of 

 elder. They are about half a line in diameter, and are 

 suspended to the most delicate silver wires. The glass 

 vessel ACB has a bell shape, and is so wide that the 

 balls g,(r, even at their greatest divergency, cannot reach 

 the stripes of tinfoil h, h within the glass. In order that 

 they may give out all their electricity, Saussure used 

 four stripes of tinfoil instead of two, each internal stripe 

 having a corresponding one on the outside. The bottom 

 BC is made of metal, and upon the edge of it is a di- 

 \idt-d scale, for measuring the divergency of the balls. 

 This instrument ofSaussure'swaa extremely sensible; but 



f if. 9. 



electronic- 

 Mr. 



Fig- 10. 



when the electricity of the armojrphere was not stron?. 



he fixed on the top of it a pointed 



long, and . he connected with the 



hook A a fine metallic wire, about 50 or 6<> * V"? 



;.t the , !>! ,,f whid, was a ball of lead of th, r '. 



ounce-, which he threw to the height of 40 <v 



and thus brought down the electricity to the ciectroine- 



ter. 



The foll.vwmor Table contains the electrical forces 

 OOTtMpondfag to the divergency of tlie ball?, ;.-, , 

 mined In- experiments. 



Distance 



of Ball, in 



quarters of 



line. 



1 . 



o 



s '. 



4 . 



5 . 



6 . 



7 . 



8 . 



9 . 



10 . 



11 . 

 12 



Corresponding 



I T.V Ol LliX- 



tridtjr. 



. 1 



. 2 

 . S 

 . 4 

 . 5 

 . 6 

 . 8 

 . 10 

 . 12 

 . 1* 

 . 17 

 . 20 



Distance 

 of BalUin 

 quartr-t M* 

 a line. 

 1:5 . 

 1* . 



15 . 



16 . 



17 . 



18 . 



19 - 



20 . 



21 . 



i . 



23 . 



Corretponilinji; 

 torm of Elec- 

 tricity. 



2.9 

 33 



40 

 41 

 48 

 52 

 56 

 60 

 64 



7. Hatty' t Electrometer for Minerals. 



This instrument consists of a needle of silver or brass, Htny'i 

 terminated by two globules, and moveable upon a pi- eUrtrome- 

 vot, which forms the upper part of a stem of the same tor lor mi- 

 metal. The needle and stem are insulated, by being t!t '"''' 

 placed upon a cylindrical support of rosin. If a finger 

 of the left hand is now placed upon the bottom of the 

 metallic stem, while the right hand presents a piece of 

 rubbed sealing wax, during a second or two, at a small 

 distance from the stem, then, if the finger is first with- 

 drawn, and afterwards the stick of sealing wax, the 

 needle will be negatively electrified, and will be ready 

 for examining the poles of a mineral that is rendered 

 electrical by heat. See Hauy's Traiiv de Physique, 

 torn. i. and Traitc de Mineralogic, torn. i. and Plate 

 VIII. Fig. 76, of that work. 



8. Singer's Electrometer constructed upon a new principle 

 of Initiation. 



In order to produce a more perfect degree of insula- 

 tion than had been before obtained, Mr Singer pro- 

 poses to inclose the insulator within a narrow channel, 

 so that the moist air in contact with it may be limited 

 in quantity, and little disposed to motion. In this way, 

 the contact of the atmosphere with the insulators will 

 be less free, ami the transition of moisture to them ne- 

 cessarily retarded. In applying this principle to the 

 perfection of the gold leaf electrometer, Mr Singer 

 makes the insulation depend on a glass tube 4 inches 

 long, and -Jth of an inch internal diameter. It i* coated 

 on every side with scaling wax ; and a brass wire .' .th or 

 r ' T th of an inch thick, and 5 inches long, passes through 

 its axis, so as not to touch any part of the tube, in the 

 middle of which it is fixed by a plug of silk. This 

 construction is .shewn in Fig. II, of Plate CCXLIX. 

 where A is a brass cap screwed upon the upper part of 

 the wire m, which keeps tlie atmosjJiere from having 

 free contact with the outside of the tube B. The gold 

 leave? are fastened at the end of the wire, and the gkvra 



Singer's 

 electrome- 

 ter upon a 

 ntw princi- 

 ple of insu- 

 lation. 



PLATE 

 CCXLIX. 

 Fig- 11- 



