Meafure of EleBr'icity iy the E>tplofton of Wirt* -■ 217 



'fingle plate-machine, it exploded five times in 1% turns of the winch. Upon applying the 

 fame teft to the double plate-machine it was found to afford very nearly, or rather more 

 than twice the quantity of electricity. All the following experiments v/ere made with the 

 (ingle "plate. 



A jar *, No. i, was applied to the prime conduflior : after four turns fome ramified 

 flaflies ftruck into the uncoated part, and at the fixth turn a fpontaneous exploflon took 

 place over the clear glafs. It muft be remarked, that the mouths of none of the jars had 

 any flopper or covering. Mr. C. then took a glafs tube, which he inferted into the jar 

 nearly to the bottom, and breathed twice through it, in order, as he faid, to render it more 

 capable of retaining its charge. This procefs, fo contrary to the received opinion of elec- 

 tricians, who carefully avoid all dampnefs,is confidered by him as of the fame nature as the 

 experiment of Brook, who found that a jar, the naked part of which was foiled by handling, 

 would retain fix times the charge without exploding, which it would have held if perfect- 

 ly clean \. I had always confidered this laft experiment as a proof that glafs, when greafed 

 by handling, does not attraiSl vapour from the air as readily as when clean ; and accordingly 

 1 have often ufed tallow as a good extemporaneous varnifli for glafs pillars. Mr. Cuthbert- 

 fon's procefs, however, had the fame effeft ; for the jar did not afterwards exhibit any flafli or 

 difpofition toexplode during thewhole evening, though itwasoccafionallychargedwith ten and 

 twelve turns. A brafs ball fupported on a (land by a flick of glafs was placed fo as to receive 

 the explofion from the jar No. i, when thus connedled with the prime condudtor. From 

 this ball hung a fmall piece of pendulum wire f, confined at each end between fmall 

 forceps conflrufled for that purpofe. The clear portion of the wire which formed part of 

 the circuit was cxaftly five inches in length. An explofion was pafled through a moderate 

 interval or length of fpark ; and this interval was gradually increafed till, at lafi, the fliock 

 became fo flrong as completely to ignite the wire and divide it near the pofitive end, 

 where a fparkling globule or two flew out ; ten turns of the machine were required to pro- 

 duce this effeft, and the length of the explofive fpark was i| inch. 



Another jar, No. 2 §, was applied to the prime conduftor along with No. r, and their 

 outfide coatings were connefted together. The fame quantity of wire as in the laft ex- 

 periment was placed in the circuit, and by the fame method an explofion was obtained, 

 which ignited and broke the wire with nearly the fame appearances as before. In this cafe 

 the number of turns were 9y, and the length of fpark ^ of an inch. 



Thefe experiments evidently confirm the refult Mr. Cuthber'tfon obtained from his former 

 trials ; namely, that the quantity of cleftrlcity to difpCrfe a given portion of wire will be 



• Height of the coating 7I inches, diameter 6J inches, both outfide meafure. Uncoated part 4I inches 

 perpendicular, though the mouth, in reality, was fomewhat fmaller than the body of the jar. Thicknefs o,iS 

 inch. Hence the furface was about 18S fquare inches, or \\ fquare foot. 



t Mifcellaneous Experiments and Remarks on Eleftricity, &c. by A. Brook. Norwich, 17S9. 



X This wire is fold at the watch-tool makers. It is of fteel flattened, and is ufed to make the fmall fpting. 

 ■of-the balarice in watches. The wire here mentioned is 0,005 '"^^ '"^ breadth and one grain in weight ; meafures 

 44I inches long. 



§ Height of the coating S I inches, diameter 6,1 inches, both outfide meafure. Uncoated part 3 J- inches 

 perpendicular, though the mouth was, as in No. i, fomewhat fmaller than the body of the jar. Thick- 

 nefs 0,17 inch. Hence the furface was about 190 fquare inches, or ij fquare foot, nearly the fame as the 

 ether jar. 



Vol,. II.— August 1798. F f the 



