1835.] BecquereVs Traite Experimental, Sfc. 153 



plex induction, and that all magnetic phenomena, belonging to this 

 class of effects, derived their origin from this induction. 



3. The last chapter in the present volume is devoted to a detail 

 of experiments, in relation to the production of electrical currents, 

 by the action of other currents, a branch of science which has been 

 entirely formed by Dr. Faraday, to which he has given the name, 

 electro voltaic induction. The experiment which laid the founda- 

 tion of these important observations was, that of employing two 

 cylinders of wood, rolling over them, in a spiral form, 12 spirals 

 formed each of 203 feet of copper wire, ^th of an inch in diameter, 

 and covered with silk, and causing one to communicate with the multi- 

 plier and the other with a pile of 100 pairs of double copper plates, of 

 4 inches square, and well charged. At the moment of contact the 

 needle underwent a deviation, then after some oscillations it returned 

 to its position of equilibrium, and was deverted again when the action 

 of the pile was interrupted, but in a contrary way ; the force of the 

 inducing current being, however, greater at the moment of contact 

 than when it is interrupted. 



But not only are electrical currents induced by currents of elec- 

 tricity, but likewise, electricity is induced by the agency of magnets. 

 This is proved in the case of common magnets, by attaching to the 

 multiplier all the elementary spirals, introducing into its axis a 

 cylinder of soft iron, and then adjusting two magnetized bars, each 

 24 inches in length, so that on one side, their opposite poles being 

 brought in contact, the two others may touch equally with the two 

 ends of the iron cylinder, in order to transform it for the time into 

 a magnet. At the moment of contact the needle deviates, then 

 assumes its equilibrium, and deviates in another manner when the 

 bars are withdrawn. 



Dr. Faraday has applied himself to the investigation of the new 

 electrical state of the substance during induction. He has named 

 this state electro-tonic, and considers it as a state of tension equivalent 

 to an electric current, at least equal to the current which is produced 

 when an induction takes place or when it is suppressed. He conceives 

 that when electric currents pass across bodies, the latter become 

 electro-tonic, and give rise to electro-chemical decompositions, the 

 current acting upon a portion of the electricity of the neighbouring 

 body in such a way as to drive off a portion and attract the remainder, 

 as happens in the disengagement of electricity by influence. In re- 

 ference to the application of the magnetic induction to the explanation 

 of the magnetic phenomena observed by M. Arago, it has been found 

 by Faraday that the electric current which is excited in a metal 

 rotating near a magnet, depends entirely as to its direction on the 

 relation of the position of the metal to the resultant of magnetic 

 action, or with the magnetic curves. 



M. M. Nobili and Antinori have suggested a method for discovering 

 the distribution of currents, produced by the influence of magnets of 

 rotating disks. This is by applying the two extremities of the wire 

 of a multiplier, terminated by two thick conical points upon the 

 rotating disk. They have likewise exhibited the analogy of Arago 

 and Faraday's researches. 



