HALL AND CAMPBELL. 



MAGNETIC EFFECTS IN SOFT IRON. 



G27 



Nernst Effect. — In Figure 3, with the magnetic field as in Figures 

 1-2, we have a longitudinal heat-current, 7///, and we take note of a 

 transverse difference of potential, AP', established by magnetic action. 

 This is the Nernst effect. This AP', as here represented, is in the 

 same direction as the A/^' of Figure 1, in which the longitudinal 

 current was electrical. In this case, we shall call the Nernst effect 

 positive ; Zahn would call it negative. Zahn uses Q for the Nernst 



Figure 3. 



Figure 4. 



coefficient with his convention as to the sign. We shall use ^Te as 

 equivalent to his — Q,, the prefix h indicating a thermal longitudinal 

 flow, the Te indicating a transverse electrical action. We have by 

 definition 



where 



dl 



the temperature-gradient along the plate. 



(3) 



Leduc E^ect. — In Figure 4, with the magnetic field and the longi- 

 tudinal heat-current as in Figure 3, we take note of the transverse 

 difference of temperature, A^', established by magnetic action. This 

 is the Leduc effect. This A^', as here represented, is in the same 

 direction as the A^' of Figure 2, in which the longitudinal current 

 was electrical. In this case, the Leduc effect is called positive. 

 Zahn uses S for the Leduc coefficient. We shall use also, in the same 

 sense, ^7]^. We have by definition 





(4) 



The longitudinal effects are defined later, in connection with an 

 account of our work on them. 



