334 THE ELECTRO-MOTIVE POWER OF HEAT. [MKMOIK XXIV. 



2d. The cold wire being sharpened to a point and 

 plunged deliberately into the mercury to the bottom of 

 the bath, the deflection was 19. 



3d. But when I touched the surface of the mercury 

 with the very point of the cold wire, there was a deflec- 

 tion of 60. 



Having laid a plate of tinned iron upon the surface 

 of some hot mercury, it was touched with the point of 

 the cold wire. There was a strong deflection of the 

 needles in the opposite direction to what would have 

 been the case had the mercury been touched and not the 

 iron. The under surface of the iron was, therefore, act- 

 ing as a hot face, and the parts round the point as a cold 

 face, being temporarily chilled by the touch of the wire. 



These results explain the anomalies observed by some 

 of those who investigated the course of thermo-electric 

 currents by means of small metallic fragments. 



It Ay^ould therefore seem that when wires of the same 

 metal are used as electromotors, the quantity of electric- 

 ity evolved depends on the quantity of caloric that can 

 be communicated in a given time. Time, therefore, under 

 these circumstances, must enter as an element of thermo- 

 electric action. In the case of a single metal, the maxi- 

 mum effect would be produced when the hot element is 

 a mass and the cold one a point. 



And, lastly, " that the quantities of electricity evolved 

 in a pile of pairs are directly proportional to the number 

 of the elements." 



In the first trials I made to determine the effect of in- 

 creasing the number of pairs in a pile, the results ob- 

 tained were contradictory ; by operating, however, in the 

 following way, the proposition was at last satisfactorily 

 determined. 



1st. The resistance to conduction was made nearly 





