RELATION BETWEEN THE VARIATION OF RESISTANCE IN BISMUTH. 249 



When this is done, we find that the decrease in the transverse effect, when the plate has 

 the form fig. 3, is due to a decrease in both effects. Similarly, the decrease, as we move 

 towards the ends, is also due to a decrease in both. 



Another plate, VIIIa, was used next. The transverse electrodes were first placed in 

 the middle, then at points 2 mm. from the ends, the transverse effect in the second posi- 

 tion was the smaller. The results, treated as in I a, showed that the decrease was again 

 due to a decrease in both effects. 



Plate VIIIa. 



Length, . 

 Breadth, . 

 Thickness, 



44-0 

 21-0 

 1-05 



Temp. 15° C. 



(¥}+<&--* 



Field. 



Trans. Effect 

 with Elect. 

 in Middle. 



Trans. Effect 

 with Elect, 

 near. Ends. 



Aw, 

 n 



v/An 

 n 



Electrodes in 

 Middle. 



°1 C 2 



Electrodes near 

 Ends. 



3,350 



-•1616 



- 1463 



•0616 



•2482 



-•69 +-74 



- -63 + -68 



6,700 



-•2371 



-•2107 



1716 



•4142 



- -67 + -72 



-•62 +-64 



11,300 



- -2612 



- -2348 



•3091 



•5559 



- -68 + -70 



- -63 + -68 



17,780 



- -2377 



- -2066 



•5009 



•7077 







In Plate X. the electrodes were first soldered on to middle points of the sides, then to 

 points 4 mm. from the end ; the variation, however, was so small that no conclusion could 

 be drawn as to its cause. This plate was also slit along the middle line, so that it had 

 the form given in fig. 3, the results were qualitatively the same, but showed a decrease 

 in E. This same plate, after being used for some time, showed a change in the field 

 strength necessary to make the effect vanish. A higher field became necessary. The change 

 was very small, and the application of equation 3 showed that the pure Hall effect had 

 increased, while the second effect remained practically constant. 



In a former paper it was shown that, in plates for which the transverse effect changes 

 sign, the field strength at which the effect vanishes is raised when the plate is hammered 

 or filed. To find what change in the pure Hall or in the second effect is concerned in 

 this, the results obtained with Plate Ib were examined ; and it would appear that the 

 pure Hall effect varies, while the second remains practically constant. 



VOL. XXXVIII. PART I. (NO. 7). 2 L 



