Pump. An important machine for extracting the air from a pipe placed in water, which, by pressure of the air, rises 33 feet in the vacuum. The same principle is applied to extract air from a close glass vessel, and it is then called an air - pump; a is a solid fitting piece drawn up from b, and leaving a vacuum from b to a, owing to which the air presses the water through the rising valve b, and the water rushing into the vacuum escapes at an orifice ; a is then pushed down again when b closes, and on being raised again makes a new vacuum.

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