before and after completion of the Voltaic Circuit, 297 



ment of this instrument, the plates could be approximated or 

 separated as required. Fig. 7 shows the arrangement; N and 

 P, the terminals of the battery ; G, the galvanometer ; a and 

 hi the plates of the electroscope; S, solution of iodide of po- 

 tassium. 



30. When the plates a and b were approximated so as to 

 permit sparks to pass at intervals of about a second, a tremu- 

 Ions motion was imparted to the needle; but when they were 

 brought so nearly in contact as to permit the discharges to 

 take place in quick succession, the needle was steadily de- 

 flected, and iodine freely evolved ; proving that chemical action 

 was occurring in each cell, and that the current is a collection 

 or an accumulation of discharges of electricity of tension ; for 

 although the circuit was completed by distinct and separate 

 discharges, still the deflection of the needle was as steady as 

 if the discs had been in actual metallic contact. 



31. The discs a and b were then separated to the distance 

 of about an inch ; a piece of tinfoil was suspended by means 

 of a thread of white silk ; the tinfoil vibrated between the 

 plates, but no effect could be produced on iodide of potassium 

 or on the galvanometer. 



32. I have already alluded to the extreme difficulty I expe- 

 rienced in effecting perfect insulation. I was anxious to as- 

 certain whether this insulation, and at the same time a high 

 state of intensity, could be obtained, and whether, in such a 

 state, any evidence of chemical action could be detected when 

 one end of the battery was in connection with the ground. 

 After many trials, I succeeded in insulating 320 cells ; and so 

 efficient was even this reduced number in point of intensity, 

 that sparks could be obtained by means of the micrometer 

 electrometer through a space of yoVo^'^ ^^ ^" inch. The ends 

 of two platinum wires were then fixed so as to rest on a piece 

 of bibulous paper saturated with a solution of iodide of potas- 

 sium. One of the wires was connected at one time with the 

 copper, and at another time with the zinc terminal of the bat- 

 tery ; while the wire attached to the other extremity was con- 

 nected with the earth. This arrangement being continued for 

 several hours, and the paper kept constantly moist, not the 

 slightest evidence of any evolution of iodine could be detected, 

 until by a momentary contact made with the further extremity 

 of the battery and the ground, either by a wire, or by touch- 

 ing it with the hand, the circuit was completed. Here we 

 have a voltaic battery the intensity of which is sufficient to 

 elicit a spark between its terminals before the circuit is com- 

 pleted, but in which antecedent thereto, the slightest chemical 

 action is not appreciable ; and this when one end is in con- 



