Barometers - General Information
From the Greek word meaning "measurer of weight or pressure."
The first barometer was invented by Torricelli in 1648 and indicated changed in atmospheric pressure by virtue of a fluctuation column of mercury. In 1847, Vidie developed the aneroid barometer which is still in use today. It is a closed box with a flexible bottom which registers even the slightest changes in atmospheric pressure. The top and the bottom of the box are held apart by a spring. Whenever atmospheric pressure increases, pressure is exerted on the box, and consequently the spring. The degree of pressure is transmitted to an indicator needle. Rises and falls in atmospheric pressure provide a reliable indication of approaching changes in the weather within the next 24 to 48 hours. The most used unit of measurement for atmospheric pressure today is the hekto-Pascal, abbreviate hPa, which can be compared to millibar (mb).