278 Mr Parker, On Contact- and Thermo- Electricity. [Nov. 23, 



Returning to our own theory, let us take as a first approximation 

 D = a + b0+c0\ 

 where a, b, c are constants. Then 



P = 0(b+2c0). 

 But P vanishes when = T : hence 



b + 2cT=0. 



Thus we have 



E=D-D o = b(d-0 o ) + c(0 2 -e*) 



= -2cT(0-0 o ) + c(6*-0*) 



= -2c(0-0 o )J2V^| (14), 



the formula of Avenarius and Tait, which has been found to agree 

 sufficiently well with experiment. 



... d (D\ F B -F A 



Again, since S^J = ~ ^~ > 



we find F B -F A =-a + c0\ 



which is satisfied by taking 



F=k0* + F, 



where k and k' are constants. 



dP 

 Hence -^ = 2kd, or the ' specific heat of electricity,' %, varies 



as the absolute temperature. Also -^ — 2k, or H = 2k0 + I. 



do 



The ' thermoelectric diagram ' of Prof. Tait is greatty simplified 

 by our results. For if co be the standard metal and M any 

 other metal, the ' thermoelectric power ' of M with reference to co, 



or \ a" , is equal to H M — H m . The standard metal is taken to 

 do 



be lead, because the ' specific heat of electricity ' of lead is zero, 



or H M constant. Hence in the diagram, the abscissa represents 6', 



and the ordinate, Hm — H*, where H M is constant. 



Lastly, let a galvanic battery have both poles of the same 

 metal, and let every part of it be kept at the constant tempe- 

 rature 0. Let L be the heat evolved when we effect in any 

 way at constant pressure the same chemical change as is produced 

 by the passage through the battery of unit quantity of electricity 

 in the direction in which the battery tends to give a current. 



