TRANSVERSE EFFECT AND ON SOME RELATED ACTIONS IN BISMUTH. 231 



the agreement between the observed and the calculated values of 1 + * is in most cases 

 close ; the discrepancies can be quite well accounted for by experimental errors in 

 measuring such small resistances. 



Section III. — On the Change of Sign of the Transverse Effect. 



In Plate 1. it was noticed that the transverse effect attained a maximum and then 

 decreased steadily with increasing fields. Other plates were then made, to see if this result 

 was observable in them ; and in some of them the maximum was reached with com- 

 paratively weak fields. With stronger fields the transverse current decreased, till finally 

 it vanished ; with still stronger fields it reappeared again, but with the opposite direction. 



With Plate VI., as originally prepared, the following results were obtained : — 



Field. 



Transverse Effect. 



Sign. 



Rotatory Coefficient. 



3-5 



01179 





3-83 



5-0 



•01648 



- 



3-74 



11-5 



•0302 



- 



2-99 



19-0 



•03595 



- 



2-15 



22-0 



•03993 



- 



2-06 



32-0 



•03787 



- 



1-35 



400 



•03183 



- 



0-88 



48-4 



•0185 



— 



0-43 



53-0 



•01625 



- 



0-35 



60-0 



0032 



- 



06 



65-0 



•0057 



+ 



0-1 



776 



•03432 



+ 



05 



87-2 



•05646 



+ 



0-74 



118-0 



11916 



+ 



1*15 



127-2 



•14305 



+ 



1-28 



Here the transverse effect is at first negative ; it increases, till with a field strength 

 between 22 x 138 '5 and 32 x 138 "5 in c.g.s. units, it reaches a maximum. After that it 

 decreases and finally vanishes between 60 and 65. It begins again, however, with increas- 

 ing fields, and continues to increase ; but now it has the opposite sign. The rotatory 

 coefficient has its greatest — and negative — value with the weakest field. 



This same plate was next shortened and narrowed, but the thickness kept as before. 

 The transverse effect was again observed ; it was still the same in character. It vanished 

 with the same field strength as in the previous experiment ; and with weak fields was 

 negative, with strong positive. 



Next the plate was made thinner by planing, and the following results were obtained : — 



Plate VI. 



Length, 



Breadth, 



Thickness, 



4-22 

 2-36 

 0-0657 



cm. 



