Mr. 0. J. Lodo-e on Thermo-electric Phenomena. 353 



o 



This being the correct expression in terms of the constants of 

 (1), one is justified in saying that (3) is erroneous — although, 

 as (5) and (3) happen to be of precisely the same form, one 

 is just as good as the other if the constants are arbitrary and 

 have no special meaning assigned to them. 



In conclusion it may be worth while just to write down the 

 physical meaning of the three constants a, b, and c y 



a=z/3t Q =zb-z 2 c, b=j3(t -z), c=-/3, . . (6) 



where t stands for the temperature of the neutral point, 



t =z- 



(7) 



and (3 stands for J times the difference of the specific heats of 

 electricity in the two metals expressed as a function of the 

 absolute temperature and divided by the temperature. Or, in 

 Avenarius's (1873) notation, 



In Tait's, 



In Thomson's, 



£ = &-&. 

 (3 = k a —k b . 



/3=J 



<r a — (Tb 



By the help of (6) we may remove the constant a from (1) 

 and write it 



e =b(z + t) + c(t 2 -£ 2 ) (8) 



The temperature for which e is a maximum is 



2c~~ ° 



The following Table gives the correct values of a, b, and c 

 for a few junctions, according to the (1863) experiments ot 

 Professor Avenarius, taking z as equal to 274. 



Metals. 



a. 



b. 



c. 



t . 



Silver and iron 



902-6 



264-4 



-81-9 



23-3 



- -734 

 + -006 

 + -879 

 +2-606 



-0147 

 -•0035 

 + •0043 



+ •0092 



224 

 275 



70 

 -9 



Copper and iron 



Silver and zinc 



Platinum and lead . . . 



The values of t are explicitly inserted in order to show that 

 the relation a=— zct is tolerably well satisfied. 

 I am, Gentlemen, 



Your obedient servant, 

 University College, London. OLIVER J. LODGE. 



Phil. Mag. S. 5. Vol. 3. No. 19. May 1877. 2 A 



