921 



calculation. So the centred and the plane-centred show coercitive 

 force, and even in a degiee much too great for steel e.g. 



In all our considerations we have left unconsidered the heat- 

 movement. The magnetic |)roperties found here are apparently always 

 represented by magnetisation-curves consisting of straight lines. 

 These broken straight lines will no doubt be rounded off by the 

 heat-movement, and consequently resemble more those under obser- 

 vation. Another cause for the rounding off must be looked for in 

 the fact that the real materials are aggiegates of crystals lying at 

 random in all directions. For the present we draw the attention for 

 the effect of this cause to the well-known theories of Fierkk Weiss. 



Institute of Theoretical Physics. 

 Utrecht, I gg ^g„^^jgj. |9^g 

 (rvoningen, S 



