1055.  A fourth helix was constructed of very thick copper wire, being one-fifth of an inch in diameter; the length of wire used was seventy-nine feet, independent of the straight terminal portions.

1056.  The principal electro-magnet employed consisted of a cylindrical bar of soft iron twenty-five inches long, and one inch and three quarters in diameter, bent into a ring, so that the ends nearly touched, and surrounded by three coils of thick copper wire, the similar ends of which were fastened together; each of these terminations was soldered to a copper rod, serving as a conducting continuation of the wire.  Hence any electric current sent through the rods was divided in the helices surrounding the ring, into three parts, all of which, however, moved in the same direction.  The three wires may therefore be considered as representing one wire, of thrice the thickness of the wire really used.

1057.  Other electro-magnets could be made at pleasure by introducing a soft iron rod into any of the helices described (1053, &c.).

1058.  The galvanometer which I had occasion to use was rough in its construction, having but one magnetic needle, and not at all delicate in its indications.

1059.  The effects to be considered depend on the conductor employed to complete the communication between the zinc and copper plates of the electromotor; and I shall have to consider this conductor under four different forms:  as the helix of an electro-magnet (1056); as an ordinary helix (1053, &c.); as a long extended wire, having its course such that the parts can exert little or no mutual influence; and as a short wire.  In all cases the conductor was of copper.

1060.  The peculiar effects are best shown by the electro-magnet (1056.).  When it was used to complete the communication at the electromotor, there was no sensible spark on making contact, but on breaking 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 electromotor, but a powerful one on breaking 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 contact, but none on making contact.