126 PROFESSOR TAIT ON A FIRST APPROXIMATION 
heat, &c. As these were all of a confessedly somewhat speculative character, 
I printed at the time only that connected with thermal conductivity, which I 
had the means of comparing with experiment, and which seemed to accord 
fairly with ForBes’ experimental results. But the assumption on which this 
was based was essentially involved in all the other portions of the paper. 
“With a view to the testing of my hypothetical result as to electric con- 
vection of heat, several of my students, especially Messrs May and StrrakeEr, last 
summer made a careful determination of the electro-motive force in various 
thermo-electric circuits through wide ranges of temperature. Their results for 
a standard iron-wire, connected successively with two very different specimens 
of copper, when plotted, showed curves so closely resembling parabolas that I 
was led to look over my former investigations and determine what, on my hypo- 
thetical reasoning, the curves should be. This I had entirely omitted to do. I 
easily found that the parabola ought, on my hypothesis, to be the curve in every 
case, and I made last August a numerous and careful set of determinations with 
Kew standard. mercurial thermometers as an additional verification. 
“‘My hypothetical result was to the effect that what THomson (Trans. R.S.E. 
1854, Phil. Trans. 1856) calls the specific heat of electricity, should be, like 
thermal and electric resistance, directly proportional in pure metals to the 
absolute temperature, the coefficient of proportionality being, for some sub- 
stances, negative. 
“Hence, using THomson’s notation as in Trans. R.S_E., we have for any two 
metals 
Jo, =hiby Jo, = kt , 
where /, and &, are constants, whose sign as well as value depends on the 
properties of each metal, ~, , ~, are the specific heats of electricity, and J is 
JouLE’s Equivalent. 
“ Thus, introducing these values into THomson’s formule, we have 
II dil 
(t, —h,) t= 3 (yo) =I(4—F), 
where IT is the Peltier effect at a junction at absolute temperature ¢ Integrat- 
ing, we have 
II 
C= fits 
or 
II 
JS = (i, Te (2, =D) , 
where ¢, is the constant of integration, obviously in this case the temperature 
at which the two metals are thermo-electrically neutral to one another. Hence 
the Peltier effect may be represented by the ordinates of a parabola of which 

