me is diminished by compression, and if it be used for cooling purposes, as in ice-making, its preliminary cooling before it is allowed to expand will make it more effective in absorbing sensible heat when freed.
Arthur, July 25, 1865.
An air-pump is combined with a series of air-vessels by means of pipes and stop-cocks, or valves, in such a manner that the air compressed into one air-vessel may be used to supply the pump when compressing air into one or more other air-vessels to a higher tension, the air entering the pump-barrel being thus already com-
Arthur's air-compressor. pressed to a certain tension.
The amount of increase in tension which the pump is required to produce need not exceed that at which it will work advantageously.
In the last reservoir in the series the air is further compressed by forcing water into the lower part thereof by means of another pump.
The air is compressed more and more by the successive operations, a single pu