26 • PHILOSOPHICAL TRANSACTIONS. [aNNO 1776. 



divergence of the electrometer was the same after the removal of the jars, as 

 before, provided it was placed at a considerable distance from them : from which 

 last circumstance, I think we may conclude, that the force with which the fluid 

 endeavours to escape from the single jar, is the same as from all the jars 

 together. 



It appears therefore, that the distance to which the spark will fly, is not sen- 

 sibly affected by the number or size of the jars, but depends only on tlie force 

 with which they are electrified ; that is, on the force with which the fluid endea- 

 vours to escape from them : consequently, a large jar, or a great number of 

 jars, will give a greater shock than a small one, or a small number, electrified to 

 such a degree, that the spark shall fly to the same distance ; for it is well known, 

 that a large jar, or a great number of jars, will give a greater shock than a small 

 one, or a small number electrified with the same force. 



In trying this experiment, the jars were charged very weakly, insomuch that 

 the distance to which the spark would fly, was not more than the 20th of an 

 inch. The electrometer I used, consisted of two straws, 10 inches long, hang- 

 ing parallel to each other, and turning at one end on steel pins as centres, with 

 cork balls, about i of an inch in diameter, fixed on the other end. The way by 

 which I estimated the divergence of these balls, was by seeing whether they 

 appeared to coincide with parallel lines placed behind them at about 10 inches 

 distance ; taking care to hold my eye always at the same distance from the balls, 

 and not less than 30 inches off. To make the straws conduct the better, they 

 were gilded, which causes them to be much more regular in their effect. This 

 electrometer is very accurate ; but can be used only when the electricity is very 

 weak. It would be easy however to make one on the same principle, which 

 should be fit for measuring pretty strong electricity. The instrument by which I 

 found to what distance the spark would fly, differs from Mr. Lane's electrometer 

 no otherwise, than in not being fixed to a jar, but made so as to be held in the 

 hand. 



I next took 4 jars, all of the same size ; electrified one of them to a given de- 

 gree, as shown by the electrometer ; snd tried the strength of the shock which 

 it gave ; and found also to what distance the spark would fly. I then took 2 of 

 the jars, electrified them in the same degree as before, and communicated their 

 electricity to the 2 remaining. The shock of these 4 jars united, was rather 

 greater than that of the single jar ; but the distance to which the spaik would 

 fly was only half as great. Hence it appears, that the spark from 4 jars, all of 

 the same size, will not dart to quite half so great a distance as that from one of 

 those jars, electrified in such a degree as to give a shock of equal violence ; and 

 consequently the distance to which the spark will fly, is inversely in a rather 

 greater proportion than the square root of the number of jars, supposing them 



