( 411 ) 



With several of the observations mentioned above the agreement 

 of the separate values was still greater. 



c. Calculation of the variation of condudivity for heat. 



Let t be the difference between the temperature in the plate and 

 that of the surrounding atmosphere, and let x be the distance from 

 the heated end, then we can assume when using certain simplifying 

 suppositions that 



dH 



■—-. — aH = 



ax-' 



OS 



in which a^^ — 



dg 



d = section of the plate. 



=z circumference of the plate. 



s = coefficient of the exterior conduction of heat. 



9= « „ „ interior „ „ „ 



We assume that s is independent of the magnetic force. 

 For t we find 



The great difficulty in the measurements with our plate of bismuth, 

 is that, as would be the case for a longer plate, we cannot neglect 

 the second term for moderate values of *• and take the coefficient 

 p constant (this could only be the case if the plate were soldered 

 immediately to the heated tube). In the magnetic field p, q and a 



28* 



