Royal Society of Edinburgh. 533 



temperatures at P and P' respectively, and if the current be in the 

 direction from P to P'. An application to the case of copper and iron 

 is made, in which it is shown that, if i P l and * 9 refer to these me- 

 tals respectively, if S be a certain temperature defined below (which, 

 according to Regnault's observations, cannot differ much from 240° 

 Cent.), and if T be any lower temperature, we have 



/, 



^{^ i (t)-^ 2 (0}d( = Q T +lF, 



J 



since the experiments made by Becquerel lead to the conclusion, that 

 at a certain high temperature iron and copper change their places in 

 the thermo-electric series (a conclusion which the author has expe- 

 rimentally verified), and if this temperature be denoted by S, we 

 must consequently have 6 =0. 



The quantities denoted by 9 and F in the preceding equation 



being both positive, it is concluded that when a thermo-electric current 

 passes through apiece of iron from one end kept at about 240° Cent., to 

 the other end kept cold, in a circuit of which the remainder is copper, in- 

 cluding a long resistance ivire of uniform temperature throughout, or an 

 electro-magnetic engine raising weights, there is heat evolved at the cold 

 junction of the copper and iron, and {no heat being either absorbed or 

 evolved at the hot junction) there must be a quantity of heat absorbed 

 on the whole in the rest of the circuit. When there is no engine raising 

 weights in the circuit, the sum of the quantities evolved at the cold 

 junction and generated in the " resistance wire " is equal to the quantity 

 absorbed on the whole in the other parts of the circuit. When there is 

 an engine in the circuit, the sum of the heat evolved at the cold junc- 

 tion and the thermal equivalent of the weights raised, is equal to the 

 quantity of heat absorbed on the whole in all the circuit except the cold 

 junction. 



7. An application of the theory to the case of a circuit consisting 

 of several different metals shows that if 



?(A,B), <£(B,C), </>(C,D) .... 0(Z,A) 

 denote the electromotive forces in single elements, consisting respect- 

 ively of different metals taken in order, with the same absolute tem- 

 peratures of the junctions in each element, we have 



0(A,B) + 0(B,O) + 0(C,D) . . +<p(Z,A)=0, 

 which expresses a proposition, the truth of which was first pointed 

 out and experimentally verified by Becquerel. A curious experi- 

 mental verification of this proposition (so far as regards the signs of 

 the terms of the equation) was made by the author, with refer- 

 ence to certain specimens of platinum wire and iron and copper 

 wires. He had observed that the platinum wire, with iron wires 

 bent round its ends, constituted a less powerful thermo-electric ele- 

 ment than an iron wire with copper wires bent round its ends, for 

 temperatures within atmospheric limits. He tried, in consequence, 

 the platinum wire with copper wires bent round its ends, and con- 

 nected with the ends of a galvanometer coil ; and he found that, with 

 temperatures within atmospheric limits, a current passed from the 



