444 



Messrs. Trowbridge and Penrose 



C-H. 



Deflections 



taken every 



minute. 



H-C. 



Deflections 



taken every 



minute. 



Differences 

 between 



the corre- 

 sponding 



deflections. 



C-H. 



Deflections 



taken every 



minute. 



H-0. 



Deflections 



taken every 



minute. 



Differences 

 between 



the corre- 

 sponding 



deflections. 



12-0 2 

 123 l 

 12-1 • 

 12-0 2 



13-0 L 

 131 2 

 13-4 2 

 128 ' 



1-0 



0-8 

 1-3 

 0-8 



14-5 • 

 143 3 

 14-3 1 

 14-8 2 



13-3 2 

 13-3 x 

 13-4 2 

 133 l 



1-2 



1-0 



•VI 



1*6 



Mean difference =097. 



Mean difference =1*15. 



The strip of nickel was now substituted for the copper, 

 every thing else remaining exactly the same. One end of the 

 nickel was heated, and the thermopile was placed on such a 

 spot that the galvanometer gave a deflection of 35 centim. 



The same current was passed as above. The results are 

 given in the right-hand table. Let d= the mean difference 

 in the first table, and d' ' = that in the second, d and d' are then 

 proportional to the elevation of temperature of the part of the 

 bars under the pile on account of the Thomson Effect. Let 

 a= coefficient of' Thomson Effect; that is, cr is such a quantity 

 that add represents the heat absorbed per unit current per unit 

 time in passing from section at temperature 6 to section at 

 temperature 6 + dd. The heat evolved in unit section when 

 the temperature is increased by \d . K is ^KfZSD, where K 

 is a constant depending on the galvanometer, S is the specific 

 heat, and D the density of the metal. If we consider the 

 Thomson Effect to be constant under the pile, and 6 and 6' to 

 represent the temperature of the ends of the space covered by 

 the pile, we have : — 



aiO-e^K^D; 

 and the similar expression for nickel, 



. a' = (T S' D' 



"a d ' S * D* " ' 



Equation (I.) then gives the relative value of the coefficient of 

 the Thomson Effect at any temperature 6. 



S-=-095, S' = '108, D = 8-9, D'=8*3, tf=0-97, ^ = 1*15 

 ■'. -=rl*25; .-. <r' = l-2ba. 



■ (I.) 



