Barometer

An apparatus for measuring the pre ure exerted by the atmosphere. It consists, in the mercurial form, of a gla tube, over 31 inches long, closed at one end, filled with mercury and inverted, with its open end immersed in a cistern of mercury. The column falls to a height proportional to the pre ure of the atmosphere from 30 to 31 inches at the sea level. The "standard barometer" is a height of the mercury or of the "barometric column" of 30 inches or 760 centimeters, measured from the surface of the mercury in the cistern. The column of mercury is termed the barometric column. Above it in the tube is the Torr i cell i an vacuum. [Transcriber's note: More accurately, 29.92 inches of mercury or 14.696 PSI.]