202 
SECOND REPORT— - 1832 . 
much smaller number than would be desirable* * * § . Fourier’s 
“thermometer of contactf,” intended for examining the con¬ 
stant of permeability, has not come into general use, as it pro¬ 
bably will do when the calculations required to be made from 
its results are adapted to variable thicknesses of the bodies 
under experiment. 
The specific heats of substances have also formed a subject of 
nice and successful investigation. MM. Dulong and Petit have 
determined those of a great number of solid bodies, and ren¬ 
dered it highly probable that the specific heats of their ultimate 
atoms are the same. De la Roche and Berard, and De la Rive 
and Marcet have signalized themselves in the more arduous in¬ 
vestigation of the specific heats of the gases. From its direct ap¬ 
plication to the condition of our atmosphere, and to the proba¬ 
ble cause of cold as we ascend through its strata, this subject 
and the whole relation of the gases to heat has offered a most 
important and interesting field for investigation during the 
present century. Laplace discussed it in the tenth book of the 
Mecanique Celeste ; the experimental part was taken up by 
Gay-Lussac and Welter, by Clement and Desormes, by De la 
Roche and Berard, by' De la Rive and Marcet, by Mr. Hay- 
craft, and finally by M. Dulong. Though this question as re¬ 
lating to different gases cannot be considered settled, the most 
probable result is that obtained by De la Rive and Marcet, 
and by Mr. Haycraft,—that equal volumes of the different gases 
have the same specific heat . The consequences to which the 
variable specific heat of the gases under different pressures 
give rise, and especially the extrication of heat which attends 
their compression, have been studied and analysed by Ivory J, 
Poisson§, Leslie||, Avogadro^[, and others. 
Our information upon the expansion of solids has not of late 
years much increased. Several fluids however have been re¬ 
examined, and the anomalous expansion of water and its point 
of greatest density have been elaborately investigated by Hall- 
strom, Miincke, and Stampfer. M. Erman has added to our 
knowledge of the anomalous effects of heat upon several other 
substances, and upon various phenomena of liquefaction**. 
* See Experiments of Despretz in the Annates de Chimie et de Phy¬ 
sique, tom. xix. His result for platinum is generally considered erroneous; 
and some experiments which I have recently made will, I believe, demonstrate 
it to be so. 
f Annates de Chimie , tom. xxxvii. 
t Philosophical Magazine, 3rd series, vol. i. 
§ Annates de Chimie, tom. xxiii. 
|| Encyclopedia Britannica, Suppl., art. Climate. 
Memoires de VAcademie Royale de Turin, tom. xxxiii, 
** Annates de Chimie, xxxviii. xh 
