492 



On the Heat-conducting Power of Mercury. 



starting from the mean value 7*52 put for 160° of the ratio 



T — t' 



r, the values of this ratio for the lower temperatures calcu- 



m — V 



lated from the formula 



const = 



T-*' y/S + 2aT + at' 



m-t' 



1+aT. 



Table V. 



T. 





T-t' 



V3 + 2«T + **' 





1+*T. 



m — t' 



e 



40 



1-6921 



7-00 



50 



1-6814 



7-04 



80 



1-6504 



718 



100 



1-6305 



7-26 



130 



1-602 



7-39 



150 



1-5837 



7-48 



160 



1-5748 



7-52 



The results of experiment thus exclude the possibility of a 

 correspondence between the two conductivities. Besides, for 



T— t' 



Tables I.— III. twice as great an increase of the values -. 



m—t' 



would in this case be found ; so that those Tables also pronounce 



pretty clearly in the same sense. 



As the question in the case of mercury was in this most simple 

 manner decided, further experiment with the simultaneous pas- 

 sage of a current would evidently have been superfluous. Preli- 

 minary experiments, made with this view, had also presented 

 difficulties arising from the circumstance that, on the passage of 

 the current from the mercury to the iron, and vice versa, strong 

 heating entered, which was not avoided by directing the current 

 in short and equal intervals. Doubtless the surface of the iron 

 was partially oxidized and thereby a considerable resistance op- 

 posed to the current. It will be generally difficult to obtain 

 equal raisings of temperature by the current, if such places of 

 passage from one material to another come into play. 



This inconvenience drops away completely when the investi- 

 gation here discussed is applied to a solid metal rod. There no 

 transition-places are present, and the action of the current can 

 be very regularly observed. I am occupied in arranging experi- 

 ments of this sort. The measurements are exactly analogous to 

 those here communicated. The expansion of the solid metal is 

 used for the determination of the temperatures m and t\ that 



