INDUCTIVE ACTION OF AN ELECTRIC CURRENT ON ITSELF. 43 



used to complete the communication at the electromotor, there was no sensible 

 spark on making contact, but on breaJcmg contact there was a very large and bright 

 spark, with considerable combustion of the mercury. Then, again, with respect to 

 the shock : if the hands were moistened in salt and water, and good contact between 

 them and the wires retained, no shock could be felt upon making contact at the elec- 

 tromotor, but a powerful one on hreaMng contact. 



1061. When the helix i or iii (1053. &c.) was used as the connecting conductor, 

 there was also a good spark on breaking contact, but none (sensibly) on making 

 contact. On trying to obtain the shock from these helices, I could not succeed at 

 first. By joining the similar ends of i and ii so as to make the two helices equivalent 

 to one helix, having wire of double thickness, I could just obtain the sensation. Using 

 the helix of thick wire (1055.) the shock was distinctly obtained. On placing the 

 tongue between two plates of silver connected by wires with the parts which the 

 hands had heretofore touched (1064.), there was a powerful shock on breaking con- 

 tact, but none on making contact. 



1062. The power of producing these phenomena exists therefore in the simple helix, 

 as in the electro-magnet, although by no means in the same high degree. 



1063. On putting a bar of soft iron into the helix, it became an electro-magnet 

 (1057.), and its power was instantly and greatly raised. On putting a bar of copper 

 into the helix, no change was produced, the action being that of the helix alone. The 

 two helices i and ii, made into one helix of twofold length of wire, produced a greater 

 effect than either i or ii alone. 



1064. On descending from the helix to the mere long wire, the followmg effects 

 were obtained. A copper wire, 0*18 of an inch in diameter, and 132 feet in length, 

 was laid out upon the floor of the laboratory, and used as the connecting conductor 

 (1059.) ; it gave no sensible spark on making contact, but produced a bright one on 

 breaking contact, yet not so bright as that from the helix (1061.). On endeavouring 

 to obtain the electric shock at the moment contact was broken, I could not succeed 

 so as to make it pass through the hands ; but by using two silver plates fastened by 

 small wires to the extremity of the principal wire used, and introducing the tongue 

 between those plates, I succeeded in obtaining powerful shocks upon the parts of the 

 mouth, and could easily convulse a flounder, an eel, or a frog. None of these effects 

 could be obtained directly from the electromotor, i. e. when the tongue, frog, or fish 

 was in a similar, and therefore comparative manner, interposed in the course of the 

 communication between the zinc and copper plates, separated everywhere else by the 

 acid used to excite the combination. The bright spark and the shock, produced only 

 on breaking contact, are therefore effects of the same kind as those produced in a 

 higher degree by the helix, and in a still higher degree by the electro-magnet. 



1065. In order to compare an extended wire with a helix, the helix i, containing 

 ninety-six feet, and ninety-six feet of the same- sized wire lying on the floor of the 

 laboratory, were used alternately as conductors : the former gave a much brighter 



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