2«1 



the metal wall, and that within the liiiuid crystalline matter a 

 magnetic field offers no thermic efïect or only a very slight one. 

 For then the efTect of' a transversal and a longitudinal field would 

 have to be equal. 



Where the influence of" a magnetic field means in the end (he direction 

 of the more or less stretched particles of the liquid crystalline substance 

 we come to the conclusion that against this directing there is only 

 important resistance to be overcome near the wall. 



Now we have accepted an action of the wall for the explanation of' 

 some extinction phenomena ^), and that in such a way that the wall 

 directs the particles parallel to itself. The resistance which is to be 

 overcome for a transversal field is quite in accordance with this 

 way of seeing the question. 



Then as regards the nature of' this resistance, we might imagine 

 it to be of elastic origin ; the particles would then get another 

 form at the cross-action of field against wall (heating), and return 

 at the disappearance of the field again elastically to their original 

 form (cooling), in which proces the longitudinal field hastens this 

 return. 



Conclusion. 



With para-azoxy-anisol the thermoeffect of a magnetic field is 

 investigated with the help of" a thermo-element of peculiar structure. 



The investigation shows that an effect is only apparent at the 

 wall of the thermo-element, which effect probably has its origin 

 in the elastic change of form of liquid crystalline particles. 



Utrecht, Febr. 19J8. 



Physical Laboratory, Institute 

 for 77ieor<Hical Physics. 



') See our first and second papers. 



