On the Hysteresis Loss in Iron. 117 



of excited activity are distributed on the anode in a strong 

 electric field. 



(6) The excited radiations from thorium due to a short 

 exposure in the presence of the emanation increase in the 

 course of several hours after removal, to three or four times 

 their initial value. 



(7) The emanations and the matter which gives rise to 

 excited activity are the result of a succession of chemical 

 changes occurring in radioactive matter. In thorium there 

 is evidence of at least four distinct chemical changes. 



Macdonald Physics Building, 

 McGill University, Montreal. 

 July 29, 1902. 



V. Effect of Temperature on the Hysteresis Loss in Iron. 

 By R. L. Wills, B.A., A.R.C.'Sc.L, 1851 Exhibition 



Scholar, St. John's College, Cambridge *. 



IT has been known for some years that for soft iron the 

 magnetic hysteresis, for a given range of magnetic force, 

 diminishes considerably as the temperature is raised. Kunz f 

 found that the curve showing the variation of hysteresis with 

 temperature for a specimen of soft iron was practically a 

 straight line, while the corresponding curves obtained by 

 Morris J f° r a specimen of iron show that the fall of 

 hysteresis is much more rapid as the critical temperature is 

 approached than during the earlier stages of heating. 



The present paper gives the results of experiments under- 

 taken at the suggestion of Professor J. J. Thomson, on the 

 effect of temperature upon the hysteresis in iron and a 

 tungsten alloy for which the effect of temperature on the 

 magnetic permeability has already been given §. 



Method. 



The method employed is that devised by Mr. Gr. F. 0. 

 Searle ||, the energy dissipated in hysteresis being readily 

 determined by observing the "throw" produced in the 

 movable coil of a sensitive electrodynamometer. Most of the 

 apparatus used was kindly furnished me by Mr. Searle. 



The movable coil of the electrodynamometer is connected 

 in series with the secondary coil wound round the speeimen,. 



* Communicated by Prof. J. J. Thomson. 



t Electrotechnische'Zcitschrift, 1894, -p. 190. 



X Phil. Map-, vol. xliv. pp. 213-254 (1897), 



$ 11. L. Wills, Phil. Mag-, vol. 1. pp. 1-21 (1900V 



i| G. F. C. Searle, Proc. Camb. Soe. vol. ix. pp. 2-6(1895), 



