530 Mr. V, J. Blyth on the Influence of 



the rod was surrounded by non-conducting material, in order 

 that the flow of heat along it might be uniform and linear. 

 Three thermoelectric junctions of copper and german-silver 

 were attached to the rod — one at the middle point and the 

 other two at a distance of 1 cm. from either end ; the junctions 

 were soldered into small radial holes drilled in the rod, The 

 poles of the electromagnet, which were 2 cms. apart, measured 

 5 cms. X 3 cms., and could be placed so as to embrace either 

 the hotter or the colder half of the rod. After the distribu- 

 tion of temperature in the rod had attained a steady state, 

 the temperatures of the three junctions were individually — 

 and as nearly as possible simultaneously — observed with re- 

 ference to a standard junction kept immersed in melting ice. 

 Several readings were taken periodically before application 

 of the field, and again several during the interval when the 

 field was applied (usually about 9 minutes) ; and this process 

 was repeated several times until a large number of readings 

 of temperatures had been obtained. From these the tempe- 

 rature-differences at the ends of that half of the rod subjected 

 to magnetization were derived, and the average of those cor- 

 responding to no field compared against the average of those 

 corresponding to the particular field applied. Various field- 

 strengths, from 650 to 3550 c.G.s. lines per sq. cm., were 

 used, but in no case did the temperature-difference with the 

 field on differ from that with the field off by more than a 

 very small amount. Moreover, the want of exact concordance 

 among the values of the temperature-differences obtained 

 showed that these were varying by small amounts through- 

 out the experiments in consequence of accidental causes. 

 Of the apparent changes produced by application of the 

 field the largest was one of o, 3 C. increase in the tempera- 

 ture-difference at the ends of the magnetized part of the rod. 

 The mean of such changes observed was about o, 07 C, 

 which would correspond to a diminution of conductivity of 

 about 1/7 per cent. Thus it appears that the effect on the 

 conductivity of bismuth of such fields is exceedingly small, 

 since, had the change amounted to ^ per cent., it could have 

 been easily detected by this method, in spite of the slight 

 fluctuations of temperature which took place during the 

 observations. The E.M.F. in the circuit composed of the 

 copper wires of the thermo-junctions and the bismuth rod 

 between them suffered considerable alteration on the appli- 

 cation of the field. Had it been assumed that this was due 

 to a change in temperature-difference, the diminution of con- 

 dnctivity indicated would have been 5'6 per cent. Cor a field 



