... The _sine
qua non_, therefore, for healthy and robust life in tropical
countries, is air cold and dry--cold to the thermometer and dry to the
hygrometer; or, in other words, dense, and containing little else than
the necessary oxygen and azote, and this supplied to a room, fresh and
fresh, in a continual current.'
He next goes on to describe the principle of his new plan of
cooling:--'The method by which I propose to accomplish this
consummation, so devoutly to be desired, is chiefly by taking
advantage of the well-known property of air to rise in temperature on
compression, and to fall on expansion. If air of any temperature, high
or low, be compressed with a certain force, the temperature will rise
above what it was before, in a degree proportioned to the compression.
If the air be allowed immediately to escape from under the pressure,
it will recover its original temperature, because the fall in heat, on
air expanding from a certain pressure, is equal to the rise on its
being compressed to the same; but if, _while the air is in its
compressed state, it be robbed of its acquired heat of compression_,
and then be allowed to escape, it will issue at a temperature as much
below the original one, as it rose above it on compression.
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