Mr. W. S. Jevons on a Sun-gauge. 35] 
to my knowledge before been taken notice of ; and I think it may 
not be unimportant, if only proving the definite nature of an- 
other principle connected with the constitution of matter. We 
know that all the “ forces,” such as electricity, heat, &c., are de- 
finitely, and after an inyariable manner produced by the changes 
of matter. I have here endeavoured to show that the time in 
which these changes are brought about is also definite, and inva- 
riably and similarly related under similar circumstances. In “Me- 
chanics,” without taking into account the ¢ime in which work is 
done, no estimate can be formed of the moving power. If we 
are able to add to the result of chemical action the ¢ime in which 
it is performed, do we not advance a step in our investigations, 
and assimilate chemical to mechanical work more closely ? 
I would only further ask,—If the equivalents of all the 
elements produce the same quantity of electricity, as Faraday has 
shown, and very different amounts of heat, can heat and electri- 
city be modifications of the same agency? For instance, an 
equivalent of zine by its oxidizement always evolves an invariable 
amount of heat and an invariable amount of electricity; an 
equivalent of copper acts similarly; but whilst the amount of 
electricity is the same as that from zine, the quantity of heat is 
only half as much. All other elements, by combining with oxygen, 
likewise develope various amounts of heat, but the same quan- 
tity of electricity. Can therefore these two imponderables be 
either modifications of the same force, or be related as cause 
and effect ? 
The propositions, then, I have endeavoured to prove in this 
paper are,— 
That electromotive force is the same as rapidity of current ;— 
that with the same positive pole the rapidity is determined by 
the amount of heat absorbed at the negative end by decomposi- 
tion, as the more heat is absorbed the longer it requires for 
absorption. 
And that every compound requires a definite and specific pe- 
riod of time for decomposition. 
Parsonstown, August 1857. 
XLI. Ona Sun-gauge. By W.S. Jnvons, Assayer, Sydney 
Branch of the Royal Mint*. 
T is, I believe, allowed that meteorologists are very imper- 
fectly supplied with instruments for measuring the heating 
effect of the sun’s rays. The actinometer of Sir John Herschel, 
though unexceptionable in principle, has been found very expen- 
* Communicated by H. E, Roscoe, Ph.D., M.A. 
