198 Memoir on the Torpedo as imitated by electricity 



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

 in the hand. The part ABCDEFGKLM is of baked wood, the rest of 

 brass; the part GKL being covered with tinfoil communicating with the 

 brass work at FG; and the part ABM being also covered with a piece of 

 tinfoil, communicating with the brass work at CD. 



406] I next took four jars, all of the same size; electrified one of them 

 to a given degree, as shewn by the electrometer; and tried the strength 

 of the shock which it gave; and found also to what distance the spark 

 would fly. I then took two of the jars, electrified them in the same degree 

 as before, and communicated their electricity to the two remaining. The 

 shock of these four jars united, was rather greater than that of the single 

 jar; but the distance to which the spark would fly was only half as great*. 



407] Hence it appears, that the spark from four 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 to be electrified in such a degree that the shock shall be 

 of a given strength. It must be observed, that in the last mentioned 

 experiment, the quantity of electric fluid which passed through my body 

 was twice as great in taking the shock of the four jars, as in taking that 

 of the single one; but the force with which it was impelled was evidently 

 less, and I think we may conclude, was only half as great. If so, it appears 

 that a given quantity of electricity, impelled through our body with a 

 given force, produces a rather less shock than twice that quantity, im- 

 pelled with half that force; and consequently, the strength of the shock 

 depends rather more on the quantity of fluid which passes through our 

 body, than on the force with which it is impelled. 



408] That no one could ever perceive the shock to be accompanied 

 with any attraction or repulsion, does not seem extraordinary ; for as the 

 electricity of the torpedo is dissipated by escaping through or over the 

 surface of its body, the instant it is produced, a pair of pith balls sus- 

 pended from any thing in contact with the animal will not have time to 

 separate, nor will a fine thread hung near its body have time to move 

 towards it, before the electricity is dissipated. Accordingly I have been 

 informed by Dr Priestley, that in discharging a battery he never could 

 find a pair of pith balls suspended from the discharging rod to separate. 

 But, besides, there are scarce any pith balls so fine, as to separate when 

 suspended from a battery so weakly electrified that its shock will not 

 pass through a chain, as is the case with that of the torpedo. 



409] In order to examine more accurately, how far the phenomena of 

 the torpedo would agree with electricity, 1 endeavoured to imitate them 



* [Arts. 573, bio, 613.] 



