Page:A Treatise on Electricity and Magnetism - Volume 1.djvu/348

experiments on the conduction of heat, and in other cases in which the mercurial thermometer is not convenient or has not a sufficient range.

According to Tait's theory, the quantity which Thomson calls the specific heat of electricity is proportional to the absolute temperature in each pure metal, though its magnitude and even its sign vary in different metals. From this he has deduced by thermodynamic principles the following results. Let $k_{a}t,\,k_{b}t,\,k_{c}t$ be the specific heats of electricity in three metals $a,\,b,\,c,$ and let $T_{bc},\,T_{ca},\,T_{ab}$ be the temperatures at which pairs of these metals are neutral to each other, then the equations

$(k_{b}-k_{c})T_{bc}+(k_{c}-k_{a})T_{ca}+(k_{a}-k_{b})T_{ab}=0$,

$J\Pi _{ab}=(k_{a}-k_{b})t(T_{ab}-t)$,

$E_{ab}=(k_{a}-k_{b})(t_{1}-t_{2})[T_{ab}-{\frac {1}{2}}(t_{1}+t_{2})]$

express the relation of the neutral temperatures, the value of the Peltier effect, and the electromotive force of a thermoelectric circuit.