4!i PHILOSOPHICAL TRANSACTIONS. [aNNO 1770. 



cuit, one against the other. For, not insulating the jar, but setting it on the 

 table, which gave the circuit and the bodies contiguous to it an advantage for 

 contracting positive electricity by the discharge ; but, at the same time, making 

 an interruption in the circuit (by introducing part of the table into it, which 

 tended to give them negative electricity) ; he could easily manage it so, that the 

 circuit contracted neither the one nor the other ; and yet, as in the former case, 

 the lateral explosion was as considerable as ever. The balls never separated. 



To vary the experiment, he placed an insulated brass ball, 2 inches in dia- 

 meter, round and smooth, so as not easily to part with any electricity it had got, 

 in the place of the rod that supported the pith balls ; and having found a situ- 

 ation in which no electricity was communicated to the circuit, he observed that 

 none was communicated to it, though, to all appearance, it received a spark of 

 about 4- of an inch in length. At least, if it had contracted any, it was so little, 

 as to make it very problematical ; whether a pith ball, or a fine thread, was 

 moved by it, or not : whereas, when he gave it the smallest sensible spark in any 

 other manner, it would attract those light bodies for a long time together. The 

 interruption of the circuit made use of in this experiment, was not by means of 

 any part of the table, but only about a yard of brass chain introduced into it, 

 and disposed between the inside of the jar and that part of the circuit, near 

 which the insulated ball was placed, n. b. The ball must not be placed near the 

 jar itself ; for, in that situation, he found, that, though it was very smooth, and 

 perfectly spherical, yet it could not be placed very near the outside of the jar 

 standing on the table, without contracting negative electricity, in a very small 

 space of time. 



These experiments threw him back into his former state of perplexity, with 

 respect to the lateral spark ; since, when the two electricities of the circuit were 

 exactly balanced, it was very little diminished, and yet the body that received it 

 was not in the least sensibly electrified. But, on reflection, he concluded, that 

 this lateral spark must be of the nature of an explosion, and consequently, that 

 an electric spark must enter, and pass out again, within so short a space of time, 

 as not to be distinguished, and leave no sensible effect whatever : for though, in 

 this case, part of the electric matter natural to the body must be repelled, to 

 make room for the foreign electricity, its restoration to its natural state was so 

 quick, that no other motion could correspond to it. This hypothesis is favoured 

 by the observation, that it is the very same thing, whether a body be introduced 

 into a circuit, or placed near it, with respect to contracting electricity ; that is, 

 whether the electric charge enter the body at one place, and go out at another, 

 or whether it be received and emitted at the same place. This lateral explosion 

 is an effect similar to a partial circuit, in which, part of the electKc matter 

 that forms the charge in an explosion, goes one way, while the rest of the 



