r 367 ] 



XLI. On the Hall Effect and Allied Phenomena. 

 To the Editors of the Philosophical Magazine. 

 Gentlemek", — 



IN the October number of the Philosophical Magazine, in 

 the paper by Mr. Livens on " The Electron Theory of 

 the Hall Effect and Allied Phenomena," there are two points 

 to which I would like to call attention. In discussing the 

 reversal of sign which often occurs in the Hall effect, in the 

 Nernst effect, in the Leduc effect, and in the von Ettings- 

 hausen effect, it is stated that, "It is, however, of importance 

 to notice in this connexion that the signs of all the effects are 

 found to be reversed if one of them is, or in other words, the 

 effects always have the same relative direction. This obser- 

 vation is important as implying that the cause of the reversal 

 is common to them all." An examination of the accompany- 

 ing table, in which the direction of these effects has been 

 indicated for a few metals, will show that the statement quoted 

 above is inaccurate. There are some metals in which the 

 reversal of signs occurs in accordance with the statement of 

 Mr. Livens, but in the majority of cases it is otherwise. 



Metal. 



Hall Nernst 



Effect. Effect. 



Leduc yo " Ettiu S 8 - 



Effect. h ™ se * 

 Effect. 



Bismuth 



Tellurium 



+ — 

 + 







+ 



Cobalt 



+ 



- + 



— -Ir- 



+ + 



_ 



Silver 



Copper 





+ 



1 



In view of this discrepancy it seems impossible to account 

 completely for this reversal of signs by a local magnetic field 

 inside of the metal. In some cases the presence of this local 

 magnetic field may afford a satisfactory explanation of the 

 reversal of signs in the effects, but it does not afford a 

 general explanation. 



