VOL. LX.] PHILOSOPHICAL TRANSACTIONS. ; 43 



charge goes another ; the only difference is, that this detached part of the charge 

 leaves the common track, and returns to it again, in the very same place. 



Several remarkable partial circuits occurred in the course of his experiments 

 before, particularly one, mentioned in the History of Electricity, p. 6g2, in 

 which, part only of the explosion passed in the shortest way, while another part 

 of it took a circuit, consisting of the same materials, 30 times as long ; and 

 another, mentioned, p. 69 1 , where one circuit was made through a thick rod of 

 metal, and another, at the same time, through the open air. 



That there is an admission and an explosion of the electric matter, in this 

 lateral explosion, seems evident, from this circumstance, that it is far more con- 

 siderable when the body that receives it is large, than when it is small. In the 

 former case, there is room for the electric matter, natural to the body, to retire, 

 on the admission of the foreign electricity belonging to the charge; whereas, in 

 the latter case, there is not room for it. When he placed a small brass ball, of 

 about a quarter of an inch in diameter, near the circuit, he could not perceive 

 that it was at all affected by any lateral explosion ; and the spark was very incon- 

 siderable, when he placed a needle, about 2 inches in length, to receive it ; but 

 when he connected the large tube above mentioned, by means of a pretty thick 

 iron wire, to any body whatever, placed in the neighbourhood of the circuit, 

 he had (with a jar of only half a square foot of coating glass) made the lateral 

 explosion, an inch or more in length, consisting of a very full and bright spark 

 of electric fire. Insulated bodies, of about 8 or Q feet in length, seem to admit 

 as large a lateral explosion as any body whatever is capable of: for, connecting 

 them with the ground, by means of the best conductors (which gave the electric 

 matter in the bodies, the freest recess possible) he could never make this explo- 

 sion much more considerable, using the same jar, and all other circumstances 

 the same. 



It is a manifest advantage in these experiments, that the lateral explosion be 

 not taken from the coating of the jar itself, or from any part of the circuit, very 

 near to it. He found that, caeteris paribus, it is the most considerable when 

 taken at the extremity of a brass rod, of one foot, or a foot and a half long, the 

 other end of which is contiguous to the jar. It is analogous to this, that the 

 longest spark is taken, not from the body of the prime conductor itself, but at 

 the extremity of a long rod inserted into it. The electric matter seems to ac- 

 quire a kind of impetus by the length of the medium through which it passes. 

 But he found that the maximum, in this case, did not exceed, or rather, that it 

 did not quite reach, 3 feet ; for, making use of a thick iron rod, 8 or 9 feet long, 

 the lateral explosion, taken at the extremity of it, was about the same, as when 

 it was taken at the end of a rod 4 inches from the jar ; and not half so consi- 

 derable as when taken at the extremity of a rod one foot long. This, he 



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