216 On Heat, and the Constitution of Elastic Fluids. 
velocity of the particles will be inversely as the square root of 
the specific gravity. Hence the specific heat will be inversely 
proportional to the specific gravity, a law which has been arrived 
at experimentally by De la Rive and Marcet. 
In the following Table I have placed the specific heats of 
various gases determined in the above manner, in juxtaposition 
with the experimental results of Delaroche and Berard reduced 
to constant volume :— 
Experimental Theoretical 
specific heat. specific heat. 
Hydrogen . . . 2°352 1506 
Oxygen: amnrshs-\i 07168 0-094. 
Nitrogen... «.{ 2) 3 -OF195 0-107 
Carbonic oxide . . 0158 0-068 
The experimental results of Delaroche and Berard are invari- 
ably higher than those demanded by the hypothesis. But it 
must be observed, that the experiments of Delaroche and Berard, 
though considered the best that have hitherto been made, differ 
considerably from those of other philosophers. I believe, how- 
ever, that the investigation undertaken by M. V. Regnault, for 
the French Government, will embrace the important subject of 
the capacity of bodies for heat, and that we may shortly expect 
a new series of determinations of the specific heat of gases, cha- 
racterized by all the accuracy for which that distinguished phi- 
losopher is so justly famous. Till then, perhaps, it will be better 
to delay any further modifications of the dynamical theory, by 
which its deductions may be made to correspond more closely 
with the results of experiment*. 
* If we assume that the particles of a gas are resisted uniformly until 
their motion is stopped, and that then their motion is renewed in the op- 
posite direction, by the continued operation of the same cause, as in the 
projection upwards and subsequent fall of a heavy body; the maximum 
velocity of the particles will be to the uniform velocity required by the 
theory assumed in the text, as the square root of two is to one, and the 
comparison of the theoretical with the experimental specific heat will be as 
follows :— 
Experimental Theoretical 
specific heat. specific heat. 
Hydrogen . . . . 2'352 3012 
RUST nk cs ben any gh OS 0°188 
Nitrogen. . . . . 07195 0214 
Carbonic oxide. . . 0:158 0136 
I have just learned that the experiments of Regnault on the specific 
heat of elastic fluids are on the eve of publication, and doubt not that their 
accuracy will enable us to arrive at a decisive conclusion as to the correct- 
ness of the above hypothesis.—June 185], J. P. J. 
