1819.] Sur UIdentité des Forces Chimiques et Electriques. 461 
received. We may likewise heat wires by the electricity of 
contact. To produce this effect, we must employ large metallic 
plates, in order to collect a great quantity of electricity relative 
to its intensity. — a 
Such is the induction, from which Prof. CErsted concludes that 
it is a general law that bodies become not whenever they are forced 
to conduct a greater quantity of electricity than they can freely 
transmit. In such cases there is always a considerable accumu- 
lation of the opposite electricities before they unite. It is this 
union of the two electricities which produces heat. Professor 
(Ersted does not explain himself with regard to the nature of 
heat. He does not inform us whether it be a substance formed 
by the union of the two electricities, as was the opinion of 
Winter. Indeed from his mode of expressing himself, he seems 
rather to be of opinion that the two electricities are not sub- 
stances, but forces ; and that heat is a force composed of the 
two opposite electrical forces united together. If this be the 
nature of his theory of heat, I confess that | am unable to form 
any accurate conception respecting it. I can conceive two 
opposite forces rendering each other imsensible by their mutual 
action ; but I cannot conceive them to unite together, and form 
a new force of a different nature. I can form a conception of 
what Winterl means when he says, that heat is a swbstance com- 
posed by the union of the two opposite electricities, provided 
these electricities be substances ; but if they are merely opposite 
forces, the affirmation that heat is produced by their union 
seems to me at least to be merely words destitute of ideas 
attached to them. 
As I am unable to perceive the accuracy of the reasoning in 
the following paragraph, in which Prof. Cérsted deduces some of 
the most striking particulars respecting heat as consequences of 
his theory, I shall present the reader with a literal translation of 
the passage. 
“« This action (the union of the two electricities) ought, there- 
fore, to disappear in a point of space just when it begins to act 
in the succeeding point. Accordingly it leaves no trace as long 
as it meets with no obstacle ; but when it meets with resistance, 
the case is quite different. The force which ought to accumu- 
late in the place where the obstacle occurs, not being at liberty 
to put itself in equilibrium with an opposite force in the prolonga- 
tion of the line, turns its action towards another point where 
there is less resistance, in order to continue to act in the same 
manner. This is what happens in the reflection of heat. The 
new direction will be determined by the direction which it had 
before, and by that of the resistance ; and may be determined 
by the fundamental principles of mechanics, which point out the 
law known to all the world that the angle of reflection is equal 
to the angle of incidence, It is easy to see that all that we have 
deduced here from our principles applies perfectly to radiant heat. 
We shall continue a little further the examination of this calorific 
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