I9I5.] ADAMS— HALL AND CORBINO EFFECTS. 49 



and thus the transverse difference of potential is 



c HI 



e = 



Thus 



^ k t 



The constant c may be determined from both the Hall and Corbino 

 effects. Experiments that Mr. Chapman has recently been making 

 show that c is the same when measured by the two effects. 



Now it is known that the Hall effect varies in sign from metal 

 to metal. This change in sign may be introduced in the hypothesis 

 by supposing that the constant c varies in sign for different metals. 

 The experiments that have been made show that the Corbino effect 

 changes in sign with the Hall effect. Thus there can be little doubt 

 that these two effects are essentially the same, and that any ex- 

 planation of one effect will explain the other. 



Corbino also showed that when a disk carrying a radial current 

 was placed in a magnetic field so that the normal to the disk made 

 an acute angle with the direction of the field, a torque was brought 

 into play tending to make the disk parallel to the field. \i (b is the 

 angle between the normal to the disk and the magnetic force, the 

 mutual energy of the circular current and the magnetic field is 



W = ^' IH'S cos2 </,, 



OTT 



where 5 is the area of the disk. Thus the torque tending to in- 

 crease (f> is 



dW c 

 — ^rr = ^ IH^S sm 20. 



0(p OTT 



Mr. Smith has succeeded in measuring this torque in four or five 

 different metals, including bismuth, and the values of c calculated 

 from his results are in good agreement with those obtained from 

 the measurement of the circular current. 



The production of a circular current in a disk by a magnetic 

 field acting on a radial current implies an increase in its resistance. 



PROC. AMER. PHIL. SOC., LIV, 2l6 D, PRINTED JUNE 21, I915. 



