124 Chronicles of Science. | Jan., 
through a sufficiently large supply of cold water (or in winter time 
of snow), the workings below might be sufficiently reduced in tem- 
perature by the re-expansion of the air on its escape, when given 
out below in the act of working the machinery, to admit of work- 
men remaining there in comfort ; at the same time the ventilation 
could be supplied. Water at 120° Fahr., or even much higher, 
would, he feared, afford but an inefficient moving power, unless 
some means could be devised (without the expense of more power 
than the gain expected) of concentrating the heat of a large quan- 
tity of warm water into a smaller. This might, perhaps, be done 
through the intervention of air alternately rarefied and condensed. 
In the discussion on this letter Mr. Binney said that at the present 
time little was known as to the difficulties we should experience in 
working coal mines at a depth of 4,000 feet from the surface. The 
exact increase of temperature in deep mines was not by any means 
well ascertained. All we can say is, that no great difficulties have 
been found in working at a depth of 2,100 feet. It must always 
be borne in mind that the deeper a mine is the greater will be the 
natural ventilation ; that is, the current caused by the air of the 
mine, at say a temperature of 80° Fahr., ascending the upcast shaft, 
while the air at the surface, of 40°, descends by the downcast shaft. 
No doubt a mine might be cooled by the expansion of compressed 
air, but it could not, so far as at present known, be done economi- 
cally. In most deep mines a considerable cooling of the air takes 
place by the expansion of the compressed gas (light carburetted 
hydrogen) as it escapes from the coal, where it has been long im- 
prisoned under great pressure ; and this has not always been allowed 
for by observers of temperature in such places. 
Mr. Pouchet has given the result of some very important 
experiments on the congelation of animals to the French Academy. 
The experiments entirely negative the popular idea that an animal 
slowly congealed may be kept so, and restored to life at any future 
time by careful thawing ; and show that an animal whose body is 
reduced to the freezing pomt throughout, is killed beyond all 
chance of revivification. The experiments have great physiological 
interest, and our readers will no doubt be glad to learn the author’s 
conclusions. These are :— 
1. That the first phenomenon produced by cold is a contraction 
of the capillary vessels to such an extent that a globule of blood 
cannot enter, these vessels therefore remain completely empty. 
2. The second phenomenon is an alteration of the blood glo- 
bules, which amounts to their complete disorganization. 
3. Every animal completely frozen is absolutely dead, and no 
power can reanimate it. 
4, When only a part is frozen, that part is destroyed by gan- 
grene. 
