536 Influence of Magnetic Field on Thermal Conductivity. 



halving the excess of the one difference over the other. More- 

 over, when a series of readings was taken with neither bar 

 in the field the rise of temperature in 80 min. of the R.H. 

 bar was found to exceed that of the L.H. bar by 3 0, 25, which 

 is midway between 4'4 and 2*1. Thus the effect of the field 

 was to diminish the rise of temperature by 1°*15, which cor- 

 responds to a diminution of the thermal conductivity of 3*1 

 per cent. ; the field in this case was 6500 c.G.S. By repeti- 

 tion of the above experiment this result was fully confirmed. 



The application of this method to bars of bismuth 4 in. 

 long, as in the case of the other methods, did not yield any 

 definite results. 



For measuring the effect of longitudinal field by the bridge 

 method, a form of bridge was used in which the arms con- 

 sisted of wires each having a right- angle bend at its ends, so 

 that its ends could dip into mercury-cups ; the arrange- 

 ment of the mercury-cups is shown in fig. 2. One of the 



Fiff. 2. 







Cold 



COPf£f? 

 BLOCrt 



~HAMBEf? 





arms was composed of a variable number of thin wires, the 

 number of which was adjusted until the temperatures of 

 the cups A and B were equal, as indicated by the sensitive 

 thermo-junctions dipping into them. The wires were all 

 coated with a thin layer of enamel, which broke the electrical 

 circuit through the bridge, thus excluding the Nernst effect 

 when magnetic fields were employed. By use of this 

 arrangement fairly good values were obtained for the con- 

 ductivity of the specimens tested by comparison with that of 

 a standard copper wire whose conductivity was assumed ; and 

 the method proved a very convenient one for this purpose. 

 For the diminution of conductivity of an iron wire under a 



