NEXT. Barometers are used to predict the weather. iStockPhoto. A barometer measures air pressure: A "rising" barometer indicates increasing air pressure; a "falling" barometer indicates decreasing air pressure. In space, there is a nearly complete vacuum so the air pressure is zero.
Keeping this in consideration, what is considered to be high barometric pressure?
When the air pressure drops, so does the mercury level." Atmospheric pressure can also be measured in millibars (mb), with a "bar" being roughly equivalent to one atmosphere of pressure (one atmosphere equals 1.01325 bars). One bar is equivalent to 29.6 in. Hg.A barometer reading of 30 inches (Hg) is considered normal.
Why do they use mercury in barometers?
Mercury is commonly used in barometers because its high density means the height of the column can be a reasonable size to measure atmospheric pressure. A barometer using water, for instance, would need to be 13.6 times taller than a mercury barometer to obtain the same pressure difference.