32 Account of an EkBrometer. 



two tubes Is cemented In a handle of turned wood, C, by which it is held in the hand; the 

 other end is clofed by a brafs cap, D ; the diftance between the extremities of the fmall 

 tube and that of the large one is filled with red wax ; B, B, on the cap D is fcrewed at 

 plcafure, either a ring E, or a brafs hook F. The ring is ufed for applying the inftru- 

 ment to the ball of a conduftor, and the hook when it is hung to a ring : on the cap D is 

 a brafs ftem G, terminating by a knob. This ftem is bended, and the extremity of its 

 knob muft be diredly beneath the line with which the graduated fcale of the fmall tube 

 commences. 



Round the large tube is a brafs ring H, half of which extends to the length of twelve or 

 fifteen lines, in the form of a half tube P, applied againft the fides of the tube. This 

 gutter ferves to mark the degrees, by Aiding along the graduated fcale by means of a but- 

 ton beneath, I. On the ring H is fixed one of the fmall ele£lrometers invented by 

 SauITure, K, K, which is furmounted by a ftem V, on which ftem is fixed at pleafure 

 either a point L, or a ball M, of the fame fize as that which terminates the ftem G, op- 

 pofite which it is placed. The extremity of this point or ball muft be placed immediately 

 over the extremify of the half tube or fcale P, and horizontally to the centre of the ball, 

 which terminates the ftem G. . 



At the top of Sauflure's ele£lrometer is a fmall ring N, which ferves to conne£l it with 

 the chain Z, when required. 



To explain the ufe of this inftrument by a fingle experiment, I charge a Leyden jar, till 

 the fpontaneous overflowing announces it to be faturated. I then place the ring E on the 

 knob of this bottle, and caufe the eleftrometer of Sauflure, armed with its point, to Aide 

 towards it. I remark the degree at which the divergence of the thread ftream commences, 

 and at that inftant I fupprefs the point, and adapt in its place the ball M. I continue to 

 advance the eledrometer of Sauflure till the eleftric preflure of the atmofphere in the jar 

 caufes the threads to diverge. I again obferve the degrees, replace the point L, and clofe 

 the fliutters of my chamber; I then continue to advance the eledrometer till the luminous 

 point appears, which again affords new degrees. Laftly, I replace the ball M, and fix 

 the chain Z to the fmall ring N; I caufe it to communicate with the exterior coating of 

 the jar, and advance the eleftrometer till the exploCon takes place. Then comparing the 

 different degrees, I afcertain the comparative difference between the refpeclive methods. 



As foon as thefe relatjve proportions have been once accurately afcertained by attentive 

 obfervations, one of thofe methods alone will be fufficient for meafuring the intenfity of 

 cleflrricity, and in faft, if the body intended to be fubmitted to examination be little 

 charged with the eleftric fluid, the diverging of the threads by means of the point, will fix 

 the limits of the cleftric atmofphere : if it be more, the preffure of the atmofphere on the 

 ball M, which is fubftituted for the point, will indicate this quantity. In Ihort, if the 

 body be loaded with a confiderablc mafs of ele£tric matter. It will be fiiown by the lumi- 

 nous point. If a Leyden jar, inftead of being pofitively, is negatively eleftrified, the 

 4 point 



