288 Prof. Thomson on the Dynamical Theory of Heat. 



" Now, by the principle of mechanical eflfect, we have 



^•280 \ 



^dt-@o)-> 





if Ff ° denote the electromotive force of a copper-iron element 

 of which the two junctions are respectively 0° and 280° C, and 

 ^dt the quantity of heat absorbed per second by a current of unit 

 strength, in passing in copper from a locality at temperature t to 

 a locality at / + dt, and in iron from a locality at t + dt to a loca- 

 lity at t* ; since the Peltier generation of heat between copper 

 and iron at their neutral point, 280°, vanishes f, and therefore 

 the only absorption of heat is that due to the electric convection 

 expressed hy f^dt ; while there is evolution of heat amounting to 

 0(, at the cold junction, and of mechanical effect by the current 

 amounting to F units of work. If we estimate the value of Fq 

 as half what it would be were the electromotive force the same 

 for all equal differences of temperature as for small differences 

 near the freezing-point J, that is, if we take Fr = i x 40m x 280, 

 the preceding equation becomes 



a 280 \ 



Mt-@QJ. 



mx40=/x©Q. 



But we found 

 Hence 



»/ 



or, according to (a), 



/•280 g 



\ Mt = mx^ {c); 



results, of which {b) shows how the difference of the aggregate 

 amount of the theoretically indicated convective effect in the two 

 metals is related to the Peltier effect at the cold junction ; and 



which acting on the unit of matter (one grain) during the unit of time (one 

 second), generates a unit of velocity (one foot per second). The " ahso- 

 lute unit of work " is the work done by the absolute unit of force in acting 

 through the unit of space (one foot). 



* That is, if B denote the algebraic excess of the specific heat of elec- 

 tricity in copper, above the specific heat of electricity in iron, according to 

 the terms more recently introduced. 



t See Proceechngs of the Royal Society, Phil. Mag. July 1854. Instead 

 of 240°, conjectured fi-om Regnault's observation when these details were 

 first published, 280° is now taken as a closer approximation to the neutral 

 point of copper and iron. 



+ See Phil. Mag. for July 1854, p. 63. 



