Experiments elucidating absence of any sparking 197 



before the jars would discharge themselves. I then electrified the same 

 jars again in the same degree as before, and separated all of them from 

 the conductor except one. It was found, that the distance to which the 

 knobs must be approached to discharge this single jar was not sensibly 

 less than the former. It was also found, that the divergence of the electro- 

 meter 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*. 



403] It appears, therefore, that the distance to which the spark will 

 fly is not sensibly affected by the number or size of the jars, but depends 

 only on the force with which they are electrified; that is, on the force with 

 which the fluid endeavours 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. 



404] 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 2Oth of an inch. The electrometer f I used consisted of two straws, 

 10 inches long, hanging parallel to each other, and turning at one end on 

 steel pins as centers, with cork balls about J 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 thirty 

 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. 



405] The instrument by which I found to what distance the spark 

 would fly is represented in Fig. 2 ; it differs from Mr Lane's electrometer } 



[Art. 604.] 



Fig. 2. 



t LArt. 249.] 



[Art. 329.] 



