142 



Dr. L. Lownds on the Thermomagnetic and 



in the magnetic field, the Hal] effect, and the conductivity 

 for heat in and out of the magnetic field for the same 

 crystal specimen. 



The change of electrical resistance and Hall effect were 

 determined along and at right angles to the chief crystallo- 

 graphic axis and at three different temperatures, viz. (1) at 

 room temperature; (2) at -79° C.; (3) at- 186° C. The ratio 

 of the conductivities for heat along and at right angles to 

 the chief crystallographic axis was determined in zero field 

 and in a field of 4980 c.G.s. units. 



§ 2. The Change of Electrical Resistance in the 

 Magnetic Field. 

 The crystalline plate abed (fig. 1) was mounted in a small 

 wooden frame ABCD, 4J- cms. long, 2J cms. wide, and 1 cm. 



Fig. 1. 

 A B 



D 



thick. A rectangular piece was cut out at abed, so that the 

 plate fitted exactly, the front surface of the crystal being flush 

 with the surface of the wood. Two such frames were used, 

 according as the effect was to be measured along or at right 

 angles to the chief crystallographic axis. A current was led 

 through the plate by means of wires soldered to the copper 

 stripslit ab, cd. These strips were firmly screwed down on to 

 the crystal, narrow strips of tinfoil being placed between 

 them and the plate in order to ensure good contact and to 

 avoid fracture. Two brass spring-contacts, e and/, served as 

 electrodes for measuring the difference of electric potential 



