Ordinary Meeting, October 31st, 1865. 
R. Angus Smith, Ph.D., F.R.S., &c., President, in the 
Chair. 
The following communication from Sir J. F. W. Herschel, 
Bart., M.A., D.C.L., F.R.S., &c., Honorary Member of the 
Society, was read by Mr. Baxendell : — 
Collingwood, October 18, 1865. 
In the printed proceedings of the ordinary meeting of the 
society on the 3rd inst., I observe a notice of a paper by 
Mr. Greaves, “ On the Internal Heat of the Earth as a Mo- 
tive Power,” in which the high temperature of the carboni- 
ferous strata, at the depth of 4,000 feet (120° Fahr.) is spoken 
of as likely to oppose an insuperable obstacle to the extraction 
ot coal from that depth. On reading this it occurred to me 
that by employing condensed air, conveyed through conduct- 
ing pipes, as a mode of working machinery at that depth — 
provided the air immediately on its condensation, and before 
its introduction into the pit, were drained of the heat developed 
in the act of condensation by leading it, in pipes exposing a 
large external surface, through a sufficiently large supply of 
cold water (or in winter time of snow) — the workings below 
might be sufficiently reduced in temperature by the re-expan- 
sion of the air on its escape, when given out below in the act 
of working the machinery, to admit of workmen remaining 
there in comfort ; at the same time that ventilation would be 
supplied. 
If you think that this suggestion would be worthy the notice 
of the author of the paper referred to, or of those members of 
'the society who may have been present at its reading, or in 
Proceedings — Lit. & Phil. Society. — Yol. Y. — No. 3— Session 1865-6. 
