204 Mr. Joule on the Electrical Origin of Chemical Heat. 
tricity may be diffused over every one of its particles, and no 
important part of the znductric charge be accumulated upon 
its under surface, yet the induction upon the earth will be as 
strong as if all that portion of force which is directed towards 
the earth were upon that surface; and the state of the earth 
and its tendency to discharge to the cloud will also be as 
strong in the former as in the latter case. As to whether 
lightning-discharge begins first at the cloud or at the earth, 
that is a matter far more difficult to decide than is usually 
supposed *; theoretical notions would Jead me to expect that 
in most cases, perhaps in all, it begins at the earth. Iam, 
My dear Phillips, ever yours, 
Royal Institution, M. Farapay. 
4th Feb. 1843. 
XXXIII. On the Electrical Origin of Chemical Heat. 
By James P. Jour, Esg.t 
i a paper{ which I read on the 2nd of last November be- 
fore the Literary and Philosophical Society of this town, 
I endeavoured to account for the heat evolved by the combus- 
tion of certain bodies, on the hypothesis of its arising from re- 
sistance to the conduction of electricity between oxygen and 
the combustibles at the moment of their union. Taking this 
view of phenomena, I showed that the heat evolved by the 
union of two atoms is proportional to the electromotive force 
of the current passing between them, in other words, to the 
intensity of their chemical affinity. 
In that paper I gave the results of my own experiments, 
and I apprehended that my numbers were below the truth 
on account of the simplicity of my apparatus. On comparing 
them, however, with the experiments of Dulong, which were 
conducted in a manner very well calculated to prevent loss of 
heat, I now find that they agree so well with the results of 
that very accurate philosopher as to show that the method I 
adopted of carrying on the combustion in the inner of two glass 
jars, while the heat evolved was measured by water placed 
between them, was not unworthy of reliance. In the following . 
table I give the results of Dulong’s experiments reduced to 
degrees Fahrenheit acquired by a pound of water. 
* Experimental Researches, Par. 1370, 1410, 1484, 
+ Read before the British Association at Manchester, 25th June 1842; 
and now communicated by the Author. 
{ Published in the Phil. Mag. S. 3. vol. xx. p. 98. 
