2014-07-29

Barometer

The barometer is the simplest instrument for measuring atmospheric pressure. The earth's atmosphere at sea level has a weight of 14.7 pounds over a square inch of surface.

This weight changes as the temperature and composition of the air mass changes. A barometer uses a substitute column of mercury fluid in place of the air. One atmosphere in a mercury barometer is equaled by a column of only 760 mm Hg.