334 THE ELECTRO-MOTIVE POWER OF HEAT. [MEMOIK 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 19V 



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 W 7 ould 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 would 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 



