]02 



Article IV. 

 Researches on the Electricity of Induction. By H. W. Dove*. 



[Memoir read before the Academy of Sciences of Berlin.] 



Introduction. 



J. HE following researches were undertaken with a view to ascer- 

 tain the effect produced by the division of a massive bar of iron 

 into bundles of wire, and by the different modes of magnetizing 

 the same upon the electric currents that are induced by it in 

 the wire which surrounds it. Bachhoffner and Sturgeon f have 

 shown that the shocks on opening a galvanic circuit is much 

 more increased by the insertion of bundles of iron wires into the 

 spiral coil forming part of the circuit, than by the insertion of 

 iron in the form of a solid bar. The manner in which the extra 

 current is produced can only be investigated by its physiological 

 action and by the brilliancy of the spark which appears when con- 

 nexion is broken in the completing wire. Besides, three actions 

 concur to produce the latter, namely, the spark of the primary 

 galvanic current, its augmentation by the action of the spiral 

 coils of the completing wire upon each other, and the effect 

 arising from the magnetism becoming evanescent in the inserted 

 iron. In the production of the physiological effects the two latter 

 causes alone concur, for a galvanic circuit which is closed by a 

 short straight wire communicates no shock on breaking. By 

 examining the secondary cuiTent instead of the extra current, 

 i. e. by allowing the spiral coil terminating the galvanic circuit 

 and surrounding the bundle of iron wire to act upon another 

 wire not in contact with but parallel to it, I Mas enabled to 

 investigate the resulting current by other rheoraetrical means 

 besides sensation and the vividness of the spark. All that now 

 remained to be done was to retain in the result the action of the 

 evanescent magnetism alone, and this I obtained by constructing 

 a differential inductor, in which two equal spiral coils inter- 

 posed in the circuit acted upon two equal secondary coils, which 

 being connected crosswise together, completely neutralized each 



* The Editor is indebted to Dr. E. Ronalds for the translation and to Prof. 

 Wheatstone for the revision of this memoir. 

 1 Annals of Electricity, i. p. 481. 



