Magnetic Field on Thermal Conductivity. 



535 



coil, which was separated from the rod by Kieselguhr insu- 

 lation \ in. thick and a tube o£ ebonite, was slight; and in 

 all cases a correction was applied for whatever slow change 

 of temperature might exist during each experiment. 



On account of the large demagnetizing factor in the case 

 of the transverse magnetization of the rod, the intensity of 

 magnetization would in this case be much smaller than that 

 produced by the longitudinal field. This may account for 

 the comparatively small value of the change produced by 

 transverse field ; for Gray and Jones * have found that the 

 change of electrical resistance of iron is dependent on in- 

 tensity of magnetization rather than directly on magnetic 

 field. 



This method was unsatisfactory on account of the difficulty 

 of securing that the initial conditions for the two comple- 

 mentary experiments should be exactly the same as to tem- 

 perature. It was found better to set up two similar bars 

 of the same material side by side with their ends fixed in 

 the steam-box, and take the two sets of time-readings 

 simultaneously. This modification was applied in the deter- 

 mination of the following result for mild steel bars. The 

 table below contains figures taken from the curves repre- 

 senting the changes of temperature at the ends of the bars. 



Time from 



instant of 



letting in 



steam. 



| 

 Magnet on Left- Hand Bar. 



Magnet on Eight-Hand Bar. 



Temp.ofK.H. 



Temp.ofL.H. 



Diff. 



Temp.ofK.H. 

 16-9 



Temp.ofL.H. 



Diff. 







159 



15-9 







16-9 







20 



26-3 



23-95 



2-35 



26-4 



249 



1-5 



40 



3425 



30-65 



3-6 



33-4 



31-7 



1-7 



60 



37-85 



33-8 



4-05 



369 



34-85 



205 



70 



39-0 



34-6 



4-4 



37'9 



35-8 



2-1 



80 



39-7 



35-25 



4-45 



38-55 



36-5 



205 



90 



40-15 



35-8 



4-35 



39-0 



369 



21 



100 



406 



36-2 



« 



39-2 



37-1 



21 



It will be seen that after an interval of 80 minutes has 

 elapsed since the steam w r as blown into the box, the tempera- 

 ture-difference becomes constant. Taking as the mean values 

 of these constant differences 4°'4 and 2°'l we find the dimi- 

 nution of the rise of either bar, as compared with what the 

 rise would have been had there been no field applied, by 

 * Proc. Roy. Soc. vol. lxvii. p. 208. 



