Laws of the Propagation of Heat. 207 
M. M. Gay-Lussac and Welter are occupied at present with 
the heat disengaged by the gases, when their volume is made 
to vary under very different pressures. They have already 
obtained several results, which they propose to submit to the 
Academy of Sciences, when their labour shall be more com- 
plete; but meanwhile they have thought it right to communi- 
cate a fact which appears to them very singular. 
It is known that when we dilate air, or any other elastic fluid, 
by enlarging the space in which it is enclosed, cold is pro- 
duced. The fact observed by these gentlemen is announced 
in the following proposition: ‘¢ The air which escapes from a 
vessel in blowing through an aperture, under any pressure what- 
ever, does not change the temperature, although the air is 
dilated in issuing from the vessel.” 
it would seem to result from this, that there is heat produced 
in the blowing of the air, and that this heat is as much more 
considerable as the difference of pressure which produces the 
blast is greater; so that the heating compensates exactly the 
cold produced by the dilatation. This fact would explain 
why heat is produced when air enters into a void space, or one 
occupied by air at a smaller pressure. It would explain also 
why the blast of the machine with the column of water at 
Schemnitz produces cold and congeals water ; whilst the blast 
of the reservoir of air of the steam-engine at Caillot, where the 
pressure is constant, and of 2.6 atmospheres, does not. affect 
the thermometer. We shall be happy to see the memoir of 
these two ingenious chemists in detail; and shall abstain mean- 
while from any remarks on the obscurity of one of the above 
statements. 
On the Temperature of the Interior of the Globe. 
Mr. Fox, in reply to Mr. Moyle, who had ascribed the ele- 
vated temperature of mines to the presence of workmen, states 
that at the mine of Treskerby, which is 840 feet deep, the tem- 
perature, two days after the departure of the workmen, was 
75.2° F., the same as during their presence, The water, 
which flows in abundance at the bottom of the mine, marked 
precisely the same degree. A thermometer, sunk some inches 
in the ground, at the bottom of the deepest gallery of the mine 
of Dolcoath, at 230 fathoms from the surface, has always 
marked, during eight months continuously, 75.5° F. In all 
this time the workmen were employed at a great distance from 
the place where the thermometer was stationed. We have no 
faith in these speculations concerning the elevated temperature 
of the lowest strata of the earth’s surface, and are inclined to 
adopt Mr, Moyle’s explanation until in possession of much more 
decided evidence than any that Mr, Fox has ad@uced, 
