146 



J)v. L. Lownds on the Thermomagnetic and 

 Table II. 



1 



Parallel to Axis. Perpendicular to Axis. 



Temperature. 



p. Temperature. 



P- 



o 



15 

 - 79 

 -186 



269000 c.g.s. 15 

 379000 - 79 

 234000 -186 



151000 c.g.s. 

 135000 

 86000 



15° 



348000 15° 



* 204000 1 



* 229000 \ 



* 232000 J 



i 



* Everdingen. 



§ 3. The Ball Effect. 

 The Hall constant C is defined by the equation 



3.H 



E = C- 



d 



where E is the difference of potential between points a and b 

 in fig. 4 when a current of strength 3 flows from A to B, the 



lines o£ force being at right angles to the plane of the plate. 

 In the above, d is the thickness of the plate. Before the 

 magnetic field is excited a and b are supposed to lie upon an 

 equipotential line, if the current 3 is from A to B, and the 

 field H in the direction indicated by the arrow, then, when 

 the Hall current is from a through the galvanometer Gr to b, 

 the effect is positive. At ordinary temperatures the sign is 

 negative for Bismuth. Two different cases were possible for 

 the measurement of the Hall effect with this crystal plate. 



