262 



THERMOELECTRIC CURRENTS. 



Hence, at a certain temperature, there is an inversion of the 

 current, and the strength then increases continuously without showing 

 a fresh inflection. This phenomenon was discovered by Gumming 

 in 1823. 



Gaugain found that the temperature of inversion depends on 

 that of the cold junction, and that for a given couple the mean of 

 the temperatures of the two junctions at the moment of inversion is 

 constant and always equal to the temperature of the maximum strength. 



273. GRAPHICAL REPRESENTATION OF THE PHENOMENA. 

 Gaugain, in a remarkable research on thermoelectrical phenomena, 

 represents their course by a graphical method by which the pre- 

 ceding laws may be readily verified. Taking for the abscissa the 

 difference t - / of the temperatures of the two junctions (the cold 

 one having a constant temperature of 20), he erects at each point 

 an ordinate proportional to the corresponding electromotive force. 



o p x p 



The following properties are observed in these curves (Fig. 63) : 

 i. They are symmetrical in reference to the maximum ordinate, 

 which verifies the law relative to the temperature of inversion ; for 

 if t m is the temperature of the maximum, and t { that of inversion, 



'o + 'i 



These curves are calculated by Gaugain to be branches of hyper- 

 bolas with a vertical axis, but they may be replaced by parabolas ; 

 the difference of the ordinates calculated for the two curves are 

 of the same order as experimental errors ; both represent equally 



