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LXVII. On the Electro-motive Former of Heat. By John 
W. Draper, M.D.^ Prof essor of Chemistry in the University 
of New York.* 
[Illustrated by Plate VL] 
Tf'ROM the memoir of M. Melloni, on the Polarization of 
Heat, inserted in the second part of the first volume of 
the Scientific Memoirs, we learn, that M. Becquerel, as well 
as himself, has made experiments to determine the quantities 
of electricity set in motion by known increments of heat. 
From these experiments they conclude, that through the whole 
range of the thermometric 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 motion 
equal quantities of electricity. 
2ndly. That the tension undergoes a slight increase with in- 
crease of temperature, a phsenomenon due to the increased 
resistance to conduction of metals, when their temperature 
rises. 
Srdly. That the quantity of electricity evolved at any given 
temperature, is independent of the amount of heated surface; 
a mere point being just as efficacious as an indefinitely ex- 
tended surface. 
4thly. That the quantities of electricity evolved in a pile of 
pairs, are directly proportional to the number of the elements. 
First, then, as to the comparative march of electric deve- 
lopment, with the rise of temperature, in the case of pairs of 
different metals. 
The experimental arrangement w'hich I have employed, is 
represented in fig. 1. (Plate VI.) A A is a glass vessel, about 
three inches in diameter, wdth a wide neck, through which 
can be inserted a mercurial thermometer 5, and one extre- 
mity of a pair of electro-motoric wires. The wires I have 
employed have generally been a foot long, and y^^th of an 
inch in diameter. The extremity s of the wires thus intro- 
duced into the vessel, ought to be soldered with hard solder : 
their free extremities dip into the glass cups d filled with 
mercury, and immersed in a trough e containing water 
and pounded ice. By means of the copper wires^’^ ^th of 
an inch thick, communication is established with the mercury 
• Communicated by the Author. 
2 H 2 
