Magnetic Properties of Iron and Nickel. 361 



current by an equation which for the larger values of H 

 would have the form 



H(j.-y=co; +&) , 





where I = 1177, C has a mean value of 1*8 x 10~ 3 , and 

 6=1*1. I is the limiting intensity of magnetization for 

 this sample of iron in the field employed. 



Similar curves have been constructed for nickel, and 

 the inverse relationship of I to i a is again clearly in 

 evidence, but the critical value of i a is higher than for 

 iron. 



(6) Experiments were now instituted to trace the influence 

 of variation of temperature on curves of I and H. The iron 

 wire having been fixed in the solenoid a hysteretic curve was 

 traced at the temperature of 16° centigrade, and immediately 

 a curve of I and H was traced for the anhysteretic state. 

 Pairs of such curves were successively traced for tempera- 

 tures of 16° 0., 645° C, 721° C, and 776° C; at higher 

 temperatures the intensity became very low, and the readings 

 were not trustworthy. The numerical results are given in 

 Table I. 



The anhysteretic curves which are drawn in Diagram II., 

 when compared with the hysteretic curves in Diagram III., 

 show that the overlapping of the latter no longer exists. It 

 is an effect of hysteresis. The anhysteretic curves, on the 

 other hand, run independently of one another, the intensity 

 of magnetization always becoming less for increasing 

 temperatures. 



When hysteresis is in action the magnetic intensity does 

 not return to its old values on reducing the magnetizing 

 force, but in the anhysteretic condition I is very nearly a 

 single-valued function of H. Thus the complexities of the 

 hysteretic isothermals disappear in the anhysteretic isother- 

 mals, and the latter are capable of being expressed by a 

 simple formula which will be discussed at the end of the 

 paper. 



The same remarks apply equally to the isothermals of 

 nickel. The numerical results are given in Table II. The 

 anhysteretic isothermals alone are given in Diagram V., 

 and for all of them the strength of the alternating current 

 was 2*3 amperes. 





