294 On the Thermoelectrical Properties of Bismuth. 



through the plate instead of the electrical current, there will 

 be produced by the action of the electromagnet a difference 

 of potential at the two points* a and h. Further, besides the 

 difference of potential at a and b, which is designated the 

 transverse " therrnomagnetic effect," there will be a difference 

 of potential at A and B called the longitudinal therrnomag- 

 netic effect; and this last, says Ettingshausen, will account for 

 the apparent effect of magnetization on the thermoelectrical 

 properties of bismuth. Both Grimaldif and LeducJ, how- 

 ever, are of opinion that the apparent longitudinal thermo- 

 magnetic effect is produced by decrease of thermal conduc- 

 tivity and thermoelectrical power. 



The alte v ation of dimensions produced by magnetization 

 can as little account for the change in the thermoelectrical 

 properties of metals as for the increase of resistance ; for, 

 besides the minuteness of the alteration of dimensions, in some 

 cases the effect of loading on the thermoelectrical power is in 

 the same direction, and in others in the opposite direction, to 

 the effect of longitudinal magnetization, as will be seen from 

 Table IV. 



Table IV. 



Metal. 



Under 



i " 



longitudinal 

 tiCiion§. 



Under longitudinal 

 magnetization || . 



Iron 



...J 



- 





Nickel 



.... 



+ 



+ 



Cobalt 



.... 



4- 





Bismuth 





■H 



_ 



There is, however, this resemblance between the effects of 

 magnetization on the thermoelectrical properties of iron and 

 on its dimensions. When an iron wire is loaded beyond a 

 certain limit, magnetization begins to produce decrease of 

 length and increase of thermoelectrical power**. 



In conclusion, when we contrast the small magnetic sus- 

 ceptibility of bismuth with the large value of its rotational 

 coefficient, and with the large decrease which can be produced 



* Ettingshausen and Nernst, Wied. Ann. xxix. 

 t Nuovo Cimento, ser. 3, vol. xxii. (1887). 

 \ Co7nptes Rendtis, 1887. 



§ A plus sign shows that the stretched metal is positive to unstretched. 

 || A plus sign shows that the magnetized metal is positive to unmag- 

 netized. 

 11 Righi, R. Ace. dei Lincei, Transunti (1884). 

 ** Cf. Ewing, loc. cit. 



