124 



Mr. J. Buchanan on the 



Hence for the thermoelectric power (e B ) at the mean tem- 

 perature t, we get 



e B = +555 + 3-96* C.G.S. units. 



The mean of e A and e B being denoted by e pt - c , we g e ^ 



e pt _ c = +566 + 3-94* C.G.S. units, 



the result quoted in equation (2) above. 



Thermoelectric Power of Carbon. 



In order to find the position of carbon on the thermoelectric 

 diagram, I determined the line on this diagram of the platinum 

 employed in the above experiments. 



A strip of commercial lead, about 80 centims. long, had the 

 platinum wires soldered to the ends. The general arrange- 

 ment of the apparatus and the precautions used were similar 

 to what have already been described above. Curve D shows 

 the results of the observations ; the ordinates and abscissas 

 being the same as in the curves A, B, C. It will be noticed 

 that the observations lie well on the mean curve, thus showing 

 that the arrangements were not defective in any essential 

 point. 

 Assuming y= K (*-«)(T-^) 



as the equation to the curve, as above, I find that T= —85° C. 

 and K ="004815 give results agreeing best with observation. 

 (See Table III.) 



Table III. 



X. 



a. 



y- 



Calculated. 



Observed. 



o 



30 

 50 

 70 

 90 

 110 

 130 



o 



131 

 »» 

 >> 

 ii 



>> 



8-67 

 207 

 346 

 505 



08-3 

 88-1 



005 

 20-6 

 347 



50-8 

 68-2 

 880 



The data for calculation are : — 



Resistance of primary circuit . 

 Mean observed E.M.F. of the Grove cell 

 employed 



= 1001 ohms. 

 \ coU } =1-75 volt. 



