PHILOSOPHICAL SOCIETY OF WASHINGTON. 253 



middle of the soft iron armature 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 galvano- 

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

 This arrangement being completed, I stationed myself near the 

 galvanometer and directed an assistant at a given word to im- 

 merse 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 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 in the magnetic meridian, although the galvanic action 

 of the battery, and consequently the magnetic power still con- 

 tinued. I was however much surprised to see the needle sud- 

 denly deflected from a state of rest to about 20° to the east, or 

 in a contrary direction, when the battery was withdrawn from 

 the acid, and again deflected to the west when it was re-immersed. 

 This operation was repeated many times in succession, and uni- 

 formly with the same result, the armature the whole time remain- 

 ing immovably attached to the poles of the magnet, no motion 

 being required to produce the efi"ect, as it appeared to take place 

 only in consequence of the instantaneous development of the 

 magnetic action in one and the sudden cessation of it in the 

 other. . . . From the foregoing facts it appears that a cur- 

 rent of electricity is produced for an instant in a helix of copper 

 wire snrrounding a piece of soft iron whenever magnetism is 

 induced in the iron ; and a current in an opposite direction when 

 the magnetic action ceases; also that an instantaneous current 

 in one or the other direction accompanies every change in the 

 magnetic intensity of the iron. 



"Since reading the account before given of Mr. Faraday's 

 method of producing electrical currents, I have attempted to 

 combine the effects of motion and induction." No increase of 

 effect was however observable. On comparing the two methods 

 separately, it was found that while the sudden introduction of 

 the end of a magnetized bar within the helix connected with the 

 galvanometer deflected the needle seven degrees, the sudden 

 magnetization of the bar when within the helix, deflected the 

 needle thirty degrees. A cylindrical iron bar was made to 



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