Description
A barometer measures air pressure. The precise pressure of the air depends upon the weather, so a barometer is useful for weather forecasting. It can also be used as an altimeter (see "how to use" a hypsometer).

The pressure sensor on this barometer is a curved tube of elliptical cross-section, partially evacuated, which changes its curvature in response to changes in atmospheric pressure. The free end of the tube is linked to the blued pointer which moves round the dial, graduated 28 – 31 inches. The brass pointer can be set to register pressure at any given time, to compare with subsequent changes. As this instrument is graduated in inches and degrees Fahrenheit, it was probably made for the English market.

The curved mercury thermometer is graduated on the Fahrenheit scale, named for the instrument maker Daniel Gabriel Fahrenheit (1686-1736) who spent many years perfecting thermometers. The Fahrenheit scale takes 32 as the freezing point and 212 as the boiling point of water.

The Bourdon tube was patented by the Paris instrument maker Emile Bourdon in 1849 and was awarded a Gold Medal at the Paris Exhibition in that year. Bourdon intended it as a steam-gauge and in that form it made a fortune for him. He sold the barometer rights to the instrument maker Félix Richard whose firm later employed the Bourdon tube in some balloon meteorographs.
29/04/2008
Created by: Dr. Anita McConnell on 29/04/2008