Movement

Barometric pressure seldom changes more than an inch or so at any given time so you should not be concerned if it does not seem to move for long periods of time. Barometric pressure also remains somewhat unchanged during very hot weather.

Still in Action

Meercury-type barometers developed in the 17th century by Torricelli are still being used today. However, most of the modern barometers use aneroids to detect air pressure. An aneroid is a tightly sealed flexible metal bellow that expands and contracts due to atmospheric pressure.

New Heights

The height to which the mercury rises in the glass tube of a barometer is directly proportional to the atmospheric pressure. This is usually measured in inches of mercury.

Sticks and Dials

Mercury barometers include the “stick” version where you read the mercury height by looking at the top of the column inside the glass tube. A dial barometer (sometimes known as wheel or banjo barometers) has a hand pointing to numbers on a dial.

A Bit of History

Evangelista Torricelli, an Italian mathematician and physicist, invented the barometer in 1643. He had also served as an assistant to astronomer Galileo. Torricelli discovered that the variation of the height of mercury from day to day was caused by changes in atmospheric pressure.

Barometers 101

A barometer is an instrument used for predicting weather changes by measuring air pressure.

Forecasting

A wireless barometer is an excellent weather forecasting device that many times also displays inside and outside temperature, humidity levels and much more.

Where Does It Go?

Many people believe a barometer must be placed on an inside wall to obtain accurate readings. However, it really makes no difference where the barometer is placed – there may be a slight temperature difference but air pressure is the same inside as well as outside.

Measuring up ....

Barometers use a measurement method termed millibars. To convert millibars to inches, multiply by 0.02953. To convert inches to millibars, multiply by 33.86.

Up and Down

Falling atmospheric pressure on a barometer indicates that stormy weather or unsettled weather conditions are approaching. A rising atmospheric pressure indicates the approach of good weather.