Water-based barometers
May 2nd, 2008What's "Water-based barometers"?
The basic idea of a water-based barometer is the same as a mercury barometer. Here is a quote from a mercury barometer.
A standard mercury barometer has a glass tube of about 30?inches (about 76?cm) in height, closed at one end, with an open mercury-filled reservoir at the base. Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir. High atmospheric pressure places more force on the reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop to a lower level in the column by lowering the force placed on the reservoir. . . . The mercury barometer's design gives rise to the expression of atmospheric pressure in inches or millimeters (torr): the pressure is quoted as the level of the mercury's height in the vertical column.
(Retrieved April 28, 2008, from "http://en.wikipedia.org/wiki/Barometer")
In short, as shown in the figure, a mercury barometer measures the atmospheric pressure by showing the height of the mercury in the tube.