BAROMETER
The barometer is a scientific instrument that
measures the pressure of the atmosphere. Weather
forecasters use barometers to deflect changes in air pressure.
Because atmospheric pressure changes with distance above or below sea
level, a barometer may also be used to measure altitude.
There are two main types of barometers: mercury and aneroid.
The barometer was invented in 1644 by an Italian physicist named
Evangelista Torricelli. His device consisted of a long glass tube filled with mercury
and then inverted into a cup of mercury. The
column of mercury in the tube fell until its top was about 30 inches above the
surface of the mercury that was in the cup. The pressure of the air on the surface of the liquid in the
cup held the mercury in the tube. By
this, Torricelli showed that the pressure of the atmosphere is equal to the
weight of a 30-inch column of mercury.
Mercury barometers used today work on the same principle as Torricelli's
device. A mercury barometer
consists of a glass tube of mercury with a reservoir at the bottom.
Any change in air pressure will cause the mercury in the tube to rise and
fall. There is a scale beside the
tube that indicates the pressure.
Besides measuring pressure, barometers are used to measure altitude.
Pilots use barometers to determine their altitude.
Hikers and mountain climbers may also use barometers to measure altitude.