VOL. LX.] PHILOSOPHICAL TRANSACTIONS. 41 



monly clone in setting it down) and made the discharge through good conductors, 

 they were all electrified positively ; and bodies placed near the circuit were the 

 same. On the contrary, if, after placing the jar on the stand, he touched the 

 knob of the wire, communicating with the inside, so as to take oft" all its re- 

 dundant electricity ; both the circuit and the neighbouring bodies contracted 

 negative electricity. 



Dr. P. had at this time quite forgot that ^pinus had made the same obser- 

 vation, on discharging a plate of air, mentioned in the History of Electricity, 

 p. 273 ; but considering what he says on that subject, he found he was mis- 

 taken with respect to the reason of this experiment not succeeding with Dr. 

 Franklin and others, who had always asserted, that the electric circuit contracts 

 no electricity at all by a discharge. For he says, that the surfaces with which 

 the doctor tried the experiment, were not large enough to make the efitct sen- 

 sible ; and that the distance of the metal plates was likewise too small, as, he 

 says, it necessarily must be in the charging of glass: whereas he could give the 

 insulated circuit as sensible electricity with a common jar, as he could with his 

 plate of air; and much more depends on the height of the charge, which must 

 have been inconsiderable in the plate of air, than the quantity of surface ; 

 which, however, may be increased at pleasure, by multiplying jars in batteries. 

 • He found, however, afterwards, that much depended on the quantity of surface 

 in the coating, and the bodies connected with them, as containing more of that 

 redundant electricity, the effect of which was seen in the hist mentioned expe- 

 riment. For when he discharged the jar, standing in contict with the prime 

 conductor, the tendency to the communication of positive electricity was so great, 

 that, in that situation, the insulated circuit contracted strong positive electricity, 

 when, every thing else remaining the same, except removing it from the con- 

 ductor, and then making the discharge, it contracted no electricity at all. 



Being now perfectly master of the electricity of the circuit in electrical ex- 

 plosions, and being able, in two different methods, to give which of the two 

 electricities he pleased ; he imagined that, if he could so balance them, as to 

 communicate neither, there would be no lateral spark, as in the abovementioned 

 experiments ; but in this he was absolutely mistaken. For, in the first place, 

 when, after setting the charged jar upon the stand, he took off", as near as he could 

 guess, one half of the redundant electricity of the inside, and left both sides 

 equally electrified (as appeared by the equal attraction of the pith balls to them 

 both), the discharge of the jar through a circuit of good conductors did not, 

 indeed, communicate the least sensible electricity to the circuit, but the lateral 

 explosion was almost as manifest as before. The pith balls, hung upon the rod 

 that received it, never separated. In the next place, he repeated this experiment 

 by balancing the two diff^erent methods of communicating electricity to the cir- 



VOL. XIII. G 



