HALL AND CAMPBELL, — MAGNETIC EFFECTS IN SOI-T IRON, G05 



netic field //, perpendicular to the lines of force, the plane A' F coin- 

 ciding with the plane of the slice, which will be traversed by a current 

 of heat going in the direction OV. Equations (1) give 



X-0, Y=&'J^'^^ Z = 0. 



" M. Voigt supposes that the force 1^ turns under the action of the 

 field as the electromotive force of the primary current in the Hall 

 phenomenon turns. One obtains, then, along the axis OA', a trans- 

 verse electromotive force A', which, referred to the unit of length, is 



(where C is the Hall coefficient, p the resistivity of the metal), or, 

 according to equation (3) [<^ = 0'^], 



X. = -^4>|?/f. (4) 



" This formula (4) gives the thermo-electric eifect according to M. 

 Voigt." 



We thus get as the expression, according to Voigt, for A", the Nernst 

 coefficient, 



d!f P 



and this is the expression which Moreau tests by means of data which 

 he gives. For example, he gives the value of ^ as —1619 for iron and 

 — 152 for copper, evidently taking <i> as the thermo-electric height of 

 lead ivith respect to the other metals. 



As to his own formula for A, Moreau says, contrasting his point of 

 view with that of Voigt, " By assuming that, only, the thermo-electric 

 electromotive forces relative to the Thomson effect turn under the 

 action of the field, I have obtained the formula 



*^ Moreau does not expressly say that K = * according to Voigt. He 



C P 



does, however, put the values of * alongside his own values of K for com- 

 parison, Moreau may have been in doubt as to the sign of the Voigt formula. 



