L 415 ] 



XXXIII. 



THE TWIST AND MAGNETIZATION OF A STEEL TUBE IN A 

 SPIEAL MAGNETIC FIELD. 



By F. E. HACKETT, MA., Ph.D., 

 Lecturer in Physics, Eoyal College of Science, Dublin. 



[Read June 25 ; published October 28, 1918.] 



The investigation of the behaviour of the ferromagnetic metals under varying 

 conditions of magnetic and mechanical stress carried out by Professor Brown 

 and described in a series of communications to the Eoyal Dublin Society has 

 shown that a number of simple relations exist between the applied stress, 

 the magnetic field, and the linear dimensions of the wires examined which 

 suggest a simple theoretical relation between them. Before seeking for 

 such a relation the effects produced by the magnetic field alone require 

 correlation. 



The connexion between the Joule effect (the change of length of iron, 

 nickel, or cobalt in a magnetic field) and the Wiedemann effect (the twist 

 of an iron, cobalt, or nickel wire in a magnetic field when a current is passing 

 through it) was long ago pointed out by Maxwell, but only in a very general 

 way. It is obvious that the current passing through a wire produces a 

 circular magnetic field. It might be expected, then, that the Wiedemann 

 effect is merely another aspect of the Joule effect due to the combination of 

 the circular magnetic field with the longitudinal field. This view of the 

 phenomenon suggests the experiment of studying the Wiedemann effect in 

 steel tubes, producing the circular field by a current along an insulated wire 

 coinciding with the axis of the tube. This experiment has been carried out 

 by S. E. Williams, 1 who has made an extensive study of this subject, but not 

 under conditions which would reveal experimentally the connexion between 

 the two effects. The tubes used were of very small diameter, and may be 

 described as hollow wires. The thickness of the tube was thus very large 

 in comparison with the radius. It was thought worth while to repeat the 



1 S. R. Williams, Phys. Rev., Mar. 1911. 



SOIENT. PKOO. E.D.S., VOL. XV., NO. XXXIII. 3 X 



