Cobalt in a Rotating Magnetic Field. 



643 



a couple and was, in consequence, twisted through an angle 

 proportional to the hysteresis loss, the two quantities being 

 connected by the formula 



W=££.0, (1) 



yov 



where W is the hysteresis loss per cubic centimetre per cycle, 

 V is the volume of the disk, K is the couple required to give 

 the suspended system a twist of one radian, and 6 is the 



Fig. 1. 



h 3 



w 





deflexion in degrees. !Since (1) does not contain the speed 

 of rotation, the method was essentially a statical one. 

 Theoretically, therefore, with everything quite symmetrical 

 about the axis of rotation, a single observation of 6 made after 



