1883.] On the Production of Transient Electric Currents. 117 



Frederick the Great. Politische Correspondenz Friedrich's des Grossen. 



Band X. 4to. Berlin 1883. The Berlin Academy. 



Tidy (Chas. M.) Legal Medicine. Part II. 8vo. London 1883. 



The Author. 



" On the Production of Transient Electric Currents in Iron 

 and Steel Conductors by Twisting them when Magnetised, 

 or by Magnetising them when Twisted." By J. A. EwiNG, 

 B.Se., F.R.S.E., Professor of Mechanical Engineering and 

 Physics in the University of Tokio, Japan, now Professor 

 of Engineering in the University College, Dundee. Re- 

 ceived October 21, 1882 * 



§ 1. A chance observation, made in the summer of 1881, drew my 

 attention to the fact that when the ends of an iron wire are connected 

 to the terminals of a galvanometer, a transient current will be 

 observed if the wire be suddenly magnetised while it is held in a 

 state of torsion, or suddenly twisted whilst in a state of longitudinal 

 magnetisation. Further inquiry showed that these currents are satis- 

 factorily explainable by reference to the results of more direct obser- 

 vations which have been made on the effects of stress on magnetism. 

 They present, however, certain features of interest, and the examina- 

 tion of them, of which a condensed account is given below, may form 

 a useful supplement to any direct investigation of the effects of stress 

 on magnetic susceptibility and residual magnetism. 



§ 2. A straight, moderately soft, well-annealed iron wire, 1 millim. 

 in diameter and 34 centims. long, was placed horizontally in an E. W. 

 position, with one end securely fixed and the other held by a twisting 

 arm, by which any desired amount of torsion might be applied. The 

 twisting arm was provided with a pointer, which travelled over a 

 graduated circular dial. The ends of the wire were connected by long- 

 leading wires to a Thomson's mirror galvanometer of 0'25 ohm resist- 

 ance, with a heavy mirror, which made it fairly suitable for ballistic 

 work. Bound the iron wire was a magnetising solenoid of 660 turns, 

 31 centims. long, in two layers, wound so as to have no longitudinal 

 component parallel to the wire. In circuit with the solenoid was a 

 single large Daniell's cell and a reversing key. The resistance of this 



* This condensed version of a paper with the above title, read before the Koyal 

 Society, November 17, 1881 (see "Proceedings," vol. 33, p. 21), together with a 

 Supplementary Note received later, is printed by order of the Committee of 

 Papers. — Gr. Gr. S. 



