Barometers

A barometer is a commonly available instrument that is typically used to measure atmospheric pressure through the use of air, water and mercury. Barometers are commonly used in predicting weather conditions where a high air pressure in an area indicates fair and clear weather and a low pressure will indicate a stormy weather. While officially Evangelista Torricelli is credited with inventing it in 1643, Gasparo Berti is also acknowledged as the creator of water barometer around nearly same time.

Various types of barometers have been invented and work in various ways. The most common types of barometers and their functioning are discussed below.

Water Based Barometers – Water based barometers are the crudest form of barometers and are the basis of weather prediction. They are alternatively referred to as “weather glass” or “ thunder glass”. This specific type is made of a glass container, which is well sealed and filled up with water up to mid level. A narrow glass tube called spout is connected to the glass body below the level of water but rises above it where it is exposed to atmosphere. When the water level in the glass tube goes higher than the water level in the container, it indicates low air pressure or stormy weather and when the water level of the spout is lower than the water level in the glass body, it will indicate high air pressure meaning clear skies. This barometer can be easily constructed at home.

Mercury Barometers – In a mercury-based barometer, a glass tube, which is sealed at one end and is about 33 inches long, is connected to a mercury filled container at base. High air pressure increases level of mercury and low air pressure leads to a decrease in the level of mercury. The atmospheric pressure is measured in “torr” named after Torricelli. A lot of changes to the design of this barometer have been made in order to make more sensitive, easier to read and to transport. These changes in design have led to the invention of barometers such as siphon, wheel, Fortin, cistern, stereometric, multiple loaded, and balance barometers.

Due to a restriction in the sale of mercury in Europe, production of new mercury barometers has completely stopped.

Aneroid Barometers – Aneroid barometers are constructed of a small, flexible box of metal known as an aneroid cell which is made of an alloy of beryllium and copper. The cell incorporates a small spring, which prevents it from collapsing. The cell expands or contacts owing to small changes in the external air pressure, which in turn drives mechanical levers, and the movements of the cell are displayed on the face of the barometer through needles.

Barographs – It is barometer which records atmospheric pressure in the form of a graph and uses the same mechanism as used in an aneroid barometer. A needle is made to move on a smoked foil or in other case, a pen on paper, which are further connected to a drum operated by clockwork.

Barometers can be very effective in weather forecasting and besides predicting pressure they can also be used in combination with wind observations to make forecasts for the next few hours.