ADDRESS OF PROF. A. M. MAYER. 491 



a galvanometer, be coiled ill the form of a helix around a magnet, 

 no current of electricity takes place in it. This is an experiment 

 which has been made by various persons hundreds of times, in the 

 hope of evolving electricity from magnetism. But if the magnet 

 be withdrawn from or introduced into such a helix, a current of 

 electricity is produced while the magnet is in motion, and is rendered 

 evident by the deflection of the galvanometer. If a single wire be 

 passed by a magnetic pole a current of electricity is induced through 

 it which can be rendered sensible.' [Henry continues :] 



"Before having any knowledge of the method given in the above 

 account, I had succeeded in producing electrical effects in the follow- 

 ing manner, which differs from that developed by Mr. Faraday, and 

 which appears to me to develop some new and interesting facts : A 

 piece of copper wire about thirty feet long, and covered with elastic 

 varnish, was closely coiled around the middle of the soft-iron arma- 

 ture of the galvanic magnet described in vol. xix of the American 

 Journal of Science, and which, when excited, will readily sustain 

 between six hundred and seven hundred pounds. The wire was 

 wound upon itself so as to occupy only about one inch of the length 

 of the armature, which is seven inches in all. The armature thus 

 furnished with the wire was placed in its proper position across the 

 ends of the galvanic magnet, and there fastened so that no motion 

 could take place. The two projecting ends of the helix were dipped 

 into two cups of mercury, and these connected with a distant galva- 

 nometer by means of two copper wires each about forty feet long. 

 This arrangement being completed, I stationed myself near the gal- 

 vanometer, and directed an assistant at a given word to immerse 

 suddenly in a vessel of dilute acid the galvanic battery attached to 

 the magnet. At the instant of immersion the north end of the 

 needle was deflected 30 to the west, indicating a current of elec- 

 tricity from the helix surrounding the armature. The effect how- 

 ever appeared only as a single impulse, for the needle, after a few 

 oscillations, resumed its former undisturbed position in the magnetic 

 meridian, although the galvanic action of the battery, and conse- 

 quently the magnetic power, still continued. I was however much 

 surprised to see the needle suddenly deflected from a state of rest to 

 about 20 to the east, or in a contrary direction, when the battery 



