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XXI. 



NOTE ON THE CHANGE OF LENGTH IN NICKEL WIRE 

 DUE TO SMALL LONGITUDINAL LOADS AND LOW 

 ALTERNATING MAGNETIC FIELDS. 



By WILLIAM BROWN, B.Sc, 

 Professor of Applied Physics, Royal College of Science for Ireland, Dublin. 



Apkil 21. Published May 19, 1914.] 



In a very interesting and complete paper by Honda and Terada' on "The 

 Change of Elastic Constants of Ferromagnetic Substances by Magnetisation," 

 there are given amongst other data the results of experiments on the change 

 of length in nickel wire under tensions varying from 1'54 x 10* to 5'24 x 10* 

 grammes per sq. cm., while subjected to continuoi^s longitudinal magnetic 

 fields up to about 400 c.g.s. units. The wire employed was 74 centimetres 

 long, and about 1 mm. in diameter, the magnetising coil being 80 cms. long 

 and 5'8 cms. internal diameter. 



It occurred to the present writer, when working at the subsidence of 

 torsional oscillations in nickel and iron wires in alternating magnetic fields, 

 that it might be well, before changing the apparatus for further experiments, 

 to find the effects of fairly low alternating magnetic fields on the change of 

 length in nickel wire when it was subjected to small longitudinal loads or 

 tensions — an experiment which, as far as the writer knows, has not hitherto 

 been made. 



The solenoid used in the experiments was 236 cms. long and 2 cms. 

 internal diameter, and contained 7707 turns of insulated wire in four layers, 

 giving an internal magnetic field of 41 c.g.s. units per ampere. The effective 



1 Phil. Mag., Jan., 1907, p. 36. 

 SCIENT. PBGC. K.D.S., VOL. XIV., NO. XXI. 3 A 



