INSTRUMENTS DISTINGUISHING ELECTRICITY. ]23 



nature and dire&ion of the fuppofed ele&ric matter undeter-of the real na- 



mined, there teems to be only two which afford the fimple ap- *••• a " d . c . ourfc 



J „...., , r of ele&ncity. 



paratus we are in the habit of diftingui filing by the name of 



infh uments. As both instruments appear to deferve more im- Two inftruments 



mediate notice than they have yet had, I have inferted them for th * ordi . nar y 



J J ' . i purpofej viz. 



in Plate VIII, where Fig. 4 reprefents the Galvanic tube, * he Ga j vanlc 

 which, by the fkilful management of Dr. Wollafton, isren-tubej 

 dered capable of diftinguifhing the courfe of electricity. The 

 ingenious Mr. Acum, of Compton Street, Soho, who fupplies 

 chemifts and philofophers with apparatus and materials of commodioufly 

 every kind, made the inftrument wliere this drawing was taken. 

 Two fine gold wires are fixed in feparate fmall glafs tubes by . . 

 fufion ; and the ends of thefe tubes are ground away till the 

 very feclion or extremity of each wire is laid bare : at the 

 other end of each tube appears a larger wire with a ball, 

 which wire communicates with the gold wire within. Thefe 

 two tubes are fixed by fufion in a larger tube, provided with 

 a conical drawn aperture, through which it can be filled with 

 water, all but a fmall vacuity or bubble, and then fealed. The 

 apparatus is then complete ; and if a ftream of electricity or 

 Galvanifm be paffed through it, the water is decompofed, and 

 of the gas thus extricated., the larger flream of hidrogen fhews 

 the minus fide. It is probable this inftrument might be of ufe 

 in atmofpherical obfervations, in cafe large ftreams of electri- 

 city fhould pafs through an elevated conductor at a low in- 

 tenfity. 



The other inftrument, Fig. 5, was conftru&ed by myfelf — and an appa- 

 about twenty years ago, from an obfervation I made that low ratus with a low 

 points ceafe to act as fuch with the plus at higher elevations, 

 than with the minus electricity. So that if two balls be infu- 

 lated, and a low point proceeds from one of them, electricity 

 will fly through the interval in a fpark if the point be plus, but 

 will be filently tranfmitted if the point be minus. 



This inftrument, like the other, may be applied to diftin- 

 guifh the atmofpheric changes ; but it will be effectual only 

 jyhen the electricity is ftrong enongh to give fparks. 



$e&ion : 



