324 THE ELECTRO-MOTIVE POWER OF HEAT. [MEMOIR XXIV. 



MEMOIR XXIV. 



ON THE ELECTRO-MOTIVE POWER OF HEAT. 



From the Philosophical Magazine, June, 1840 ; Harper's Magazine, No. 328. 



CONTENTS: Experimental arrangement to determine the electro-motive 

 power. Temperatures calculated from quantities of electricity. In- 

 crease of tension with increase of temperature. Depends on increased 

 resistance to conduction. Quantity of electricity independent of heated 

 surface. In thermo-electric piles the quantity of electricity is propor- 

 tional to the number of pairs. Best forms of construction of thermo- 

 electric pairs. 



FROM the Memoir of M. Melloni "On the Polarization 

 of Heat," inserted in the second part of the first volume 

 of Taylor's " Scientific Memoirs," we learn that M. Bec- 

 querel, as well as himself, had made experiments to de- 

 termine the quantities of electricity set in motion by 

 known increments of heat. From these experiments 

 they conclude that through the whole range of the ther- 

 mometric scale those quantities are directly proportional 

 to each other. 



But as thermo-electric currents are now employed in 

 a variety of delicate physical investigations, and as there 

 appears to be much misconception as to their character, 

 I propose in this Memoir to show 



1st. That equal increments of heat do not set in mo- 

 tion equal quantities of electricity. 



2d. That the tension undergoes a slight increase with 

 increase of temperature, a phenomenon due to the in- 

 creased resistance to conduction of metals when their 

 temperature rises. 



3d. That the quantity of electricity evolved at any 



