Thermoelectric Properties of Crystalline Bismuth. 335 



§ 6. The Transversal Effect. — This was calculated in 

 accordance with the formula used by Yamaguchi *, viz. : — 



dt 



where the positive X-axis is the direction of the current of 

 heat, q the electromotive force between two points on a line 

 at right angles to this direction and distant /3 apart, and m a 

 quantity depending upon the field-strength and temperature, 

 but in the first approximation independent of the fall of tem- 

 perature. The direction of q as found by v. Ettingshausen 

 and -Nernst f can be determined by means of the following 

 rule : — ''Suppose one placed in the direction of the lines of 

 force so that they enter at the feet and leave at the head, and 

 to be looking at the same time along the direction of the flow 

 of heat, then the electromotive force is directed from left to 

 right. " In the following an electromotive force in this 

 direction is reckoned positive, as both v. Everdingen and 

 Yamaguchi have observed forces directed in the opposite 

 direction. In the measurement of the transversal effect it is 

 to be noted that copper electrodes were used. It is impossible 

 to place these exactly upon an isothermal line (the fall of 

 temperature is in some cases as much a« 124° C. per cm.). 

 Hence there exists a thermoelectric force between the points 

 before the magnetic field is excited. On putting on the field 

 there will be a rotation of the isothermal lines and a cor- 

 responding change of the thermoelectric force. The readings 

 were taken quickly in order to avoid this error as much as 

 possible. Yamaguchi used electrodes of electrolytic bismuth. 

 This diminished the thermoelectric force considerably, but 

 the error due to rotation of the isothermal lines was 

 unavoidable. 



The results for both Cases 1 and 2 of § 3 are given in 

 Tables V. and VI., and represented in the curves fig. 6. 

 The full-line curve represents the results when the crystallo- 

 graphic axis is parallel to the current of heat, and the broken- 

 line curve when the axis is at right angles to the current of 

 heat. The abscissoe are field-strengths, the ordinates cor- 

 responding values of m. 



* E. Yamaguchi, Ann. d. Phys. i. p. 214 (1900). 

 t A. von Etting-shausen & W. Nernst, Wied. Ann. xxix. p. 343 

 (1886). 



