of Electro-magnetic Experiments. 453 



1st. That the spark and shock obtained from an oleclro- 

 magnet, on breaking battery communication, are not the spark 

 and shock of the battery nor of the electro-magnet^ but, most 

 probably, the electricity induced on the wire of the helix by 

 the electricity of the battery, or, if it be true that a current 

 passes along the wire, the electricity intercepted in its passage 

 from the copper to the zinc. 



2nd. That the spark and shock do not depend, except 

 within certain limits, on the size of the battery. 



3rd. That they confirm what I ventured to assert at the last 

 meeting of the British Association (1835) on the nature of mag- 

 netism. 



4th. That the real power of the battery is not increased but 

 diminished by the electro-magnetic, or rather, electro-galvanic 

 helix. 



1st. The spark and shock (the latter of which I do not re- 

 collect to have seen remarked before,) obtained with an elec- 

 tro-magnet on breaking battery communication, are not the 

 spark or shock of the battery^ for neither one nor the other 

 can exist until after battery communication is actually broken. 

 Again, if they arise from the battery, to receive the shock it 

 would be necessary to form a part of the communication be- 

 tween the copper and zinc. This, however, is not required ; 

 it is necessary only to form a part of the communication be- 

 tween the extremities of the helix, or between one extremity 

 of the helix and either the copper or zinc of the battery. 

 Neither does the shock or spark arise from the influence of 

 the bar of soft iron inclosed in the helix : on the conti'ary, the 

 retention of magnetism in the bars, either from the nature of 

 its iron or the action of a keeper, will proportionably diminish 

 the effect ; and I have no doubt that if a large portion of mag- 

 netism were retained in a powerful electro-magnet by the 

 keeper, and the keeper were torn off" with violence from 

 the magnet, a shock and spark would be perceived at the mo- 

 ment of disruption, which, together with those obtained when 

 battery communication was broken, would form a spark and 

 shock exactly equal to what were obtained had there been no 

 retention of magnetism by the keepers when battery commu- 

 nication was interrupted. 



Of the apparatus submitted to the Society for the purpose 

 of demonstrating the facts contained in this paper by experi- 

 ment, the pait to which it was desired more particularly to di- 

 rect attention consisted of 588 feet of copper wire, No. 13, 

 coiled in seven helices of H^ feet each, on a thin brass tube, 5\ 

 inches in length, | internal diameter, having discs of brass, 

 4 inches in diameter, attached to its extremities. The tube 



