8 BRLL SYSTEM TECHNICAL JOURNAL 



from that employed 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 armature of a galvanic 

 magnet . . . which, when excited will readily sustain between six 

 and seven hundred pounds. The armature thus furnished with wire 

 was placed in its proper position across the ends of the magnet and 

 fastened so that no motion could take place. The two projecting 

 ends of the helix were connected with a distant galvanometer by 

 means of two copper wires each about forty feet long. This arrange- 

 ment being completed, I stationed myself near the galvanometer and 

 directed an assistant at a given word to suddenly immerse 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 electricity from the helix surrounding the armature. The 

 effect, however, appeared only as a single impulse, for the needle 

 after a few oscillations, resumed its former undisturbed position, 

 although the action of the battery was still continued. I was, how- 

 ever, much surprised to see the needle suddenly deflected from a 

 state of rest to about 20 to the east, when the battery was suddenly 

 withdrawn from the acid, and again deflected to the west when it 

 was re-immersed. This operation was repeated many times in suc- 

 cession, and uniformly with the same result." 



It w^as in this same paper that Henry announced his observation 

 of the phenomenon of self-induction, a most important discovery 

 and one for which he holds full credit for having first made it known 

 to the world. He writes, "I may, however, mention one fact which 

 I ha\e not seen noticed in any work, and which appears to me to 

 belong to the same class of phenomena as those before described; it 

 is this: when a small battery is moderately excited by diluted acid, 

 and its poles, which should be terminated by cups of mercury, are 

 connected by a copper wire not more than a foot in length, no spark 

 is perceived when the connection is either formed or broken; but 

 if a wire of thirty or forty feet long be used instead of the short wire, 

 though no spark will be perceptible when the connection is made, 

 yet when it is broken by drawing one end of the wire from its cup of 



mercury, a vivid spark is produced The effect appears 



somewhat increased by coiling the wire into a helix." In a some- 

 what later paper we find the following statement. "A ribbon of 

 sheet copper nearly an inch wide, and twenty-eight and a half feet 

 long, was covered with silk, and rollcfl into a flat spiral similar to the 

 form in which woolen binding is found in commerce. With this a 



