I'll' 



15 



Profs. A. Gray and E. T. .1 

 Fio. 4. 



10 



so 



too 



ISO 



200 



JBO 



ZOO 



550 



Figs. 5, 6, 7 show A< as a function of B 4 , I 4 , I li respectively. 



Of these, fig. 6 approximates closely to a straight line except in the 

 neighbourhood of the origin. It may thus be stated as an empirical 

 result for the specimen of soft iron and for the range of magnetisation 

 employed in these experiments that the change of resistance is ap- 

 proximately proportional to the fourth power of the magnetisation. 



Note added, June 18. The results are complicated to some extent 

 by hysteresis. It was found that when the iron wires were first 

 thoroughly demagnetised, and after having been left long enough to 

 take the temperature of the surroundings, were subjected to a rather 

 strong magnetising current, kept in for less than a second, so that no 

 appreciable heating could arise, about a third of 8<f> remained after the 

 magnetic force was removed. 



The above experiments were carried out in the Physical Laboratory 

 of the University College of North Wales, and we wish to take this 

 opportunity of expressing our high appreciation of the value of the 

 assistance of two students of the College, Mr. Guy Barlow and Mr. 

 Godfrey Rotter, who, by making many measurements and calculations, 

 enabled us to complete the work. 



