Manometer

Instrument for measuring the pre ure of a fluid. The unit usually employed is called an ATMOSPHERE (q.v.). The instrument consists of a vertical U tube, open at both ends (open-air manometer), or closed at one end (compre ed air). In the former case the pre ure is measured by the length of the column of mercury it will sustain; i.e., 76 cm. or 29.9 in. for each atmosphere. The closed manometer may consist of a straight tube containing air, the open end dipping IMG:content-1237.png:[graphic] IMG:content-1238.jpg:[blocks in formation] surface of mercury in the cistern, forces it up the tube, thus compre ing the air; the pre ure applied is always inversely proportional to the volume of the inclosed air. See GAUGE.