Physios. — ''Contributions to the studj/ of liquid crystals. IV. A 

 thermic E^ffect of the Magnetic Field". Bj Dr. W. J. H. Mou. 

 and Prof. L. S. Ohnstkin. (Communicated by Prof. W. H. 

 Julius). 



(Communicated in the meeting of March 23, 1918). 



The fact that the particles of liquid crystalline substances are directed 

 by a magnetic field, justifies the question whether perhaps the 

 action of the field, may entirely or partially manifest itself as heat. 

 We shall in this paper develop the results of an investigation into 

 this matter. 



We made use of an arrangement for this investigation, w^hich in 

 the main points is the same as that described in our previous 

 paper ^) on the subject. The p-azoxj^-anisol was again heated in a little 

 gold beaker, being within a little oven which was heated by elec- 

 tricity. But our little oven had to serve in this case as thermostat, 

 and above all it was necessary, that the temperature inside of the 

 oven was as far as possible equal everywhere, so that a temperature 

 gradient within the substance to be investigated would be excluded. 

 Instead of our original, very primitive little oven we fitted up as 

 such a brass tube 10 cm. long and 2 cm. wide, provided along 

 pretty well the whole length with a single widening of their manganin 

 wire, closed off at the bottom by a brass plate, at the top by a 

 brass screw-stopper, in which only a narrow opening to leave pas- 

 sage to the thermo-element. To present a current of air along the 

 heating- wire, the latter was wrapped up in chenille, and closely 

 around this there was a double brass mantle, through which water 

 circulated of the temperature of the room. 



This arrangement was put (with the axis of the little oven in a 

 vertical direction) between the poles of a Dubois-niagnet, and its 

 (horizontal) field may be looked upon as homogeneous at the place 

 of the beaker. The magnet could be turned round a vertical axis. 



The electromotive force of the thermo-element was almost fully 

 compensated, the changes arising were registered by photography. 



In our investigation as to whether the connection of the magnetic 

 field has a thermic effect, we arrived in the beginning at results, 



1) Compare the foregoing paper, 



