Influence of Magnetic Field on Thermal Conductivity, 529 



require also a heat; of at least incandescence to volatilize the 

 silicon in order to produce the bright unreversed lines seen 

 in fig. 3 at wave-length 2882, and wave-lengths from 2542 

 to 2507. 



Jefferson Physical Laboratory, 

 Harvard University, Cambridge, U.S. 



LV. On the Influence of Magnetic Field on Thermal Con- 

 ductivity. By Vincent J. Blyth, M.A. (Glasgow), 1851 

 Exhibition Research Scholar, Emmanuel College, Cambridge*. 



IN a circuit composed of bismuth and another metal, the 

 thermo-electric E.M.F. is altered if the bismuth be 

 placed in a magnetic field. This alteration was observed by 

 Leducj and by RighiJ, while using such a circuit as a 

 means of measuring the difference of temperature between 

 two points of a heat-conveying bar of bismuth. Assuming 

 that the change represented a change in the temperature- 

 difference between the junctions, they deduced the result 

 that the thermal conductivity of bismuth was altered by the 

 magnetic field. But von Ettingshausen and Nernst§ have 

 shown that such a change in the E.M.F. takes place without 

 any alteration of temperature-difference, and that it repre- 

 sents the " longitudinal thermomagnetic effect/'' which may 

 also be regarded as an alteration of the thermoelectric nature 

 of bismuth by application of magnetic field If. If thermo- 

 electric junctions are to be used for observing temperature- 

 differences with a view to measuring the effect of magnetic 

 field on thermal conductivity, it is necessary that the in- 

 trusion of the von Ettingshausen and Nernst effect should be 

 prevented ; and this may be done either by keeping the 

 junctions out of electrical contact with the bar under test, or 

 by obtaining the temperature-differences by independent ob- 

 servations of the two temperatures in each case with reference 

 to a standard junction, It is the purpose of this paper to 

 describe a number of experiments made with a view to 

 determining the effect of magnetic field on thermal con- 

 ductivity. 



A cast rod of bismuth (14 cms. long and 1 cm. in diameter) 

 was warmed at one end to 100° C. and kept at zero at the 

 other end ; the ends of the rod were soldered into large 

 copper blocks within the heating and cooling chambers, and 



* Communicated by Prof. J. J. Thomson, F.E.S. 



t Journ. de Phys. (2) vi. p. 370. % Compt. Send. CV. p, 168 (1887), 



§ Wied. Ann. xxxi. p. 760 (1887). 



% See Lownds, Phil. Mag-. Oct, 1901. 



