732 Mr. W. A. Jenkins on the Effect of a 



temperature change of the nickel, as the compensating 

 nickel resistance was of slightly larger resistance than the 

 one under observation. This creep was corrected for in the 

 results obtained. 



Experiments were carried out at the temperature of the 

 room 18° C. and at a temperature of 93°"5 C. This latter 

 temperature was obtained by enclosing the nickel in a glass 

 tube round which steam was passed. Liquid air was also 

 used, but the low temperature affected the nickel wire in 

 such a way, that the strain caused by switching on the mag- 

 netic field was sufficient to snap the wire. Jn all the 

 experiments the wire was demagnetized by reversals before 

 any readings were taken. 



L ongitudin a I Fiel d. 



Fig. 1, PI. X. shows the curve obtained wdien the nickel was 

 placed in the field longitudinally. The resistance increases 

 fairly rapidly with the magnetic field until H = 350, then the 

 increase becomes much less rapid until H = 1000, when a 

 maximum increase in resistance is observed. After 



H = 1000, -fj- decreases slightly, but this is probably due 



to the resistance being incorrectly placed in the longitudinal 

 field. An error in setting of 1°*5 would account for the 

 decrease, and in one experiment it was absent altogether. It 

 was thought posssible that with a constant magnetic field 

 the resistance might vary with the electric force, i. e. with 

 the current. Currents varying from *1 to *001 ampere 



were used, but -^- was found to be constant within these 

 limits. K 



Fig. 2, PI. X. shows a complete hysteresis cycle. The loops 

 are to be expected on account of the slight decrease of 

 resistance after reaching the maximum. The resistance 

 alteration shows a distinct lag, and does not reach zero until 



r/Ti 



a reverse field of H = 50 is reached, after which -^^ becomes 



Jtt 



negative before commencing to increase again at H = 72. 



Fig. 3, PI. X. shows the hysteresis curve at a temperature 

 of 93°'5 C. The maximum resistance increase occurs at 

 H = 320, a much lower value than is necessary at the 

 ordinary temperature. The decrease, after reaching a maxi- 

 mum, is much greater than before and cannot be explained 

 away so easily. 



Fig. 4, PI. X. shows the effect of a transverse magnetic field 



