42 PROCEEDINGS OP THE AMERICAN ACADEMY 



In other words, it was SJiid that the heat 9 — the amount of heat 

 absorbed in unit time by unit current in crossing the hot junction 

 exceeding that evolved at the cold junction — was sufficient to produce 

 a current of strength I. 



Now, when a current from an outside source is passed through 

 the circuit in the same direction as /, an amount of heat 9 (7 disap- 

 pears, — C being the strength of the external current : what becomes 

 of this heat? A certain amount of energy disappears : what is its 

 equivalent ? 



If the heat 9 is sufficient to produce a curi-ent of sti'ength I, the 

 beat 9 is great enough to produce a current G times as strong as 

 /.•.a current of strength CI. 



When the current G is passing through the circuit we should then 

 expect to find it increased (or decreased) by a current GI — the 

 equivalent of the amount of heat absorbed by G. Thus, when an 

 external current passes through a thermo-electric element, we should 

 expect to have as the total current in the circuit, C-j-/± Ci; that 

 is, the resultant current should be much greater (or much less) than 



(7+7. 



But, in several experiments that were made, it was observed that 

 the resultant current always equalled exactly G-\-L 



Now, if the Peltier effect is the cause of the thermo-electric cur- 

 rent, enough heat has disappeared to create a current G times as strong 

 as the proper thermo-electric current ; but experiment shows that the 

 thermo-electric current is perceptible, while this other current is imper- 

 ceptible. We must, therefore, conclude that this current, which is 

 equivalent to an amount of heat 9 G, is not G times as great as the 

 proper thermo-electric current ; and hence the proper thermo-electric 

 current cannot be the equivalent of the amount of heat 9. In other 

 words, the Peltier effect cannot be the cause of the thermo-electric 

 current. 



An unsuccessful experiment was made to prove that the Peltier 

 effect was not great enough to be the cause of the thermo-electric 

 current. The failure was due to the fact that the heat absorbed was 

 too small to be measured. The principle of the experiment was as 

 follows : — 



Place the thermo-electric junction in a vessel of mercury, after 

 heating the mercury to a certain temperature let it cool, the circuit 

 being broken so that no current passes. From a thermometer placed 

 in the mercury read the temperatures at definite times, and construct a 

 curve, having the temperatures as ordiuates, and the cori-espouding 



