1889.] Stress and Strain and the Properties of Matter. 



13 



III. " The Influence of Stress and Strain on the Physical Pro- 

 perties of Matter. Part III. Magnetic Induction {continued). 

 The Internal Friction of Iron, Nickel, and Cobalt, studied 

 by Means of Magnetic Cycles of very minute Range."* 

 By Herbert Tomlinson, B.A., F.R.S. Received August 

 22, 1889. 



(Abstract.) 



The author has already studied the internal friction of metals by 

 the method of torsional oscillations, and deduced certain simple laws 

 relating thereto. One of the principal objects of the present enquiry 

 was to ascertain how far the dissipation of energy resulting from 

 statical molecular friction which occurs in magnetic cycles of very 

 minute range would be amenable to the laws of dissipation of energy 

 occurring in torsional cycles. The " ballistic " method of observa- 

 tion has been employed, the arrangements being exceedingly sensitive 

 so as to admit of the use of very feeble magnetising forces. 



The following is a summary of the results obtained : — 



1. When a rod of iron, nickel, or cobalt is made to pass through a 

 complete magnetic cycle of sufficiently minute range of magnetising 

 force, the changes of magnetic induction can be expressed by an 

 equation of the form — 



y — Aa + Bx 2 , 



where x represents the change of magnetising force as the force 

 passes from its greatest value in the cycle to zero, if the force be 

 always applied in the same direction, or as the force passes from its 

 greatest value in the one direction to its greatest value in the opposite 

 direction, if the force be alternately applied in one direction and in 

 the opposite, y represents the corresponding change of magnetic 

 induction, and A and B are constants throughout the cycle. 



2. The values of A and B are the same for magnetic cycles of 

 different ranges of magnetising force, provided the force does not 

 exceed certain limits. These limits vary considerably with the nature 

 of the metal and with the mechanical or thermal treatment to which 

 it may have been subjected. 



3. The constant A is a measure of the magnetic permeability of 

 the metal when the magnetising force is infinitesimal. The product 

 of B and the cube of the maximum force in the cycle is a measure of 



* In prosecuting this research the author has received assistance from the 

 Elizabeth Thompson Science Fund, U.S.A., and from the English Government 

 Grant Fund. 



