Law of Cooling. 61 



make r- = at the point x x we have 



or 



Under the same conditions if ^=00, or is large enough to 

 oint Xx we have 



x 



^ r 

 #«g~ = J Phv n dx. (7) 



X 



h= \ V hv n dx lv 



I dX 



The equation (7) is found to express fairly some recent 

 observations of Mitchell,* who has determined the conduc- 

 tivity of iron by Forbes's method. The value of 11 for his 

 1 YaJ' square bar I find to be 1 *26. The equation (7) would no 

 doubt give k v with great accuracy if, instead of the tempera- 

 tures at different points of the bar in the " statical " experi- 

 ment of Forbes being determined by thermometers sunk in 

 holes in the bar, which thus break the continuity of the bar, 

 they were determined by thermojunction, either fixed in the 

 bar or movable as in the experiments of Wiedemann and 

 Franz. 



■Trans. Roy. Soc. Ed., July, 18S7. 



