concerned in the Phenomena of ordinary Electricity, <SfC. 455 



spirit, or by the vapour of aether if breathed ; but it is contracted 

 by light or by opium in excess. Finally, in conformity with all 

 these instances of manifold causes of the same effect, painful 

 shocks may be produced by the action on the nerves of either 

 the electric or voltaic agent, supposing them different ; for in 

 both cases these peculiar influences pass absolutely through the 

 body ; and it is most probable that, could any other influence be 

 found which is capable of passing through the body with equal 

 rapidity, it would excite the sensation of an electric shock. 



Whether the agent which causes the shock of an electro-mag- 

 netic coil is different from all others, is a question which I shall 

 not attempt to discuss : whether it is or is not different, the ex- 

 planation of this shock is, in my opinion, irreconcileable with the 

 received doctrine of the identity of the electric and voltaic agents, 

 and it will be proper to state my reasons for coming to that con- 

 clusion. 



A single voltaic combination of one square inch in surface, 

 composed of zinc and platinum, cannot be made to affect the 

 most sensible electrometer, nor to give the slightest sensation of 

 a shock, nor the least appearance of a spark. But make a circuit 

 with two very long copper wires lying closely together, but pre- 

 vented from touching by interposed silk, and the apparatus be- 

 comes capable of communicating shocks that are absolutely in- 

 supportable : hundreds of such may be given in a minute by the 

 coil apparatus now in common use, and brilliant sparks may also 

 be obtained*. Professor Jacobi thus states his first attempt to 

 repeat this experiment : — " Two copper wires 400 feet long and 

 three-quarters of a line in diameter, carefully covered with silk 

 ribbon, were coiled together in a helix round a hollow cylinder 

 of wood one inch and a half in diameter ; the ends of these two 

 wires were united in a single one. The effect of this combina- 

 tion was beyond all my expectations; for by employing a voltaic 

 pair of silver and zinc plates which had only a surface of half a 

 square inch, I obtained at the moment of disjunction a brilliant 

 spark, and a violent shock which could scarcely be boi-ne. The 

 same effects took place when the pair of plates was reduced to a 

 wire of platina and zinc. After having placed a cylinder of soft 

 iron in the hollow of the wooden cylinder, the action was still 

 more considerable. The effects were not much increased by the 

 enlargement of the surface of the pairf." 



* Some of the modern discoveries on this subject were anticipated nearly 

 half a century since in an observation made by Vassali-Eandi, one of the 

 earliest cultivators of galvanism : " with a pile of fifty pairs he found that the 

 fluid passed along a copper wire plated with silver 1151 feet in length, in a 

 time incommensurable ; the shock in this case was three times as strong as 

 i hni experienced by immediately touching lite two extremities of the pile." — 

 Philosophical Magazine, vol. xv. lKO.'i. 



t Scientific Memoirs, July 18.'<7, p. 530. 



