CONCLUSIONS FROM VOLTA's LAW. 263 



well the results of experiment. Theory indicates, as we shall see 

 later, that the curve which represents electromotive forces as a 

 function of temperature must, in effect, be a parabola. 



2. If a horizontal line is drawn through a point M 1? which 

 corresponds to the temperature / 15 the ordinates, counted from this 

 straight line, will represent electromotive forces relative to the tem- 

 perature /j for the cold junction. The law of successive temperatures 

 is thus found to be verified, for we have 



that is to say, 



The temperature of inversion corresponds to the point where 

 the new line of the abscissa meets the curve. If OP represents the 

 temperature of the cold junction, OP' will be that of inversion ; it 

 will be seen that it depends on the temperature of the cold junction. 



3. If the curves AB and AC represent electromotive forces for 

 couples formed of a metal A associated respectively with two metals 

 B and C, the difference MN of the ordinates of the two curves 

 represents the electromotive force of the couple formed by the two 

 metals B and C. The relation MP = PN + NM is therefore equivalent 

 to the equation 



E(AB) = E(AC) + E(CB), 



which expresses the law of intermediate metals. 



274. CONCLUSIONS FROM VOLTA'S LAW. Disregarding the 

 principle of inversion, we may look upon the preceding laws as 

 consequences of the principle of Volta that is to say, that there is 

 an electromotive force at the contact of two metals^ and that this elec- 

 tromotive force is a function of the temperature. 



On this view, the electromotive force of a couple is the algebraical 

 sum of the two electromotive forces in contrary directions which 

 exist at the two junctions. 



Let us agree to represent by the symbol the electromotive 



force H of contact of two metals A and B, at the temperature /, we 

 shall have 



