The History Of The Barometer

It’s still common to see a barometer on many boats along with the ship’s clock although how many people rely on them these days is debatable.

Prior to readily available broadcast weather forecasts, the barometer was a valuable instrument for predicting weather on board ships.

The barometer was invented in Italy in the early 17th Century by Evangelista Torricelli.

The word barometer is a combination of the Greek word “baros” meaning weight and “metron” meaning measure.

The first barometer used water and required a tube 35 feet long. Torricelli soon substituted mercury for water which only required a tube 32 inches long.

The tube of mercury is held vertically with the open end at the bottom in an open reservoir of mercury with a vacuum at the closed end.

The atmospheric pressure or weight of the air in the earth’s atmosphere pressing down on the reservoir of mercury pushes the mercury up the tube. As the atmospheric pressure varies, the height of the mercury in the tube varies between 28 and 31 inches. Initially atmospheric pressure was measured in inches rather than the hectopascals used today.

It took almost 200 years for a detailed weather forecasting system to come into wide use using barometric pressure. This system was invented in 1860 by Admiral Fitzroy who had earlier been captain of the Beagle on Darwins voyage of exploration.

Around the same time the aneroid barometer was invented by Frenchman Lucien Vidie. This is the type of brass barometer with a dial and pointer we generally see on boats today. Its low cost and ease of transport saw the aneroid barometer replace the mercury barometer except in professional weather stations. The aneroid barometer uses a small metal box which has a vacuum inside and a spring to stop it collapsing. As the atmospheric pressure changes the metal box expands or contracts slightly. A mechanical connection between the box and the needle causes the needle to move showing the change in pressure.

This cheap reliable barometer enabled mariners to predict the weather with a falling barometer indicting bad weather or strong winds.

Of course in the digital age electronic barometers are readily available although you can’t beat the traditional brass instrument for looks and simplicity.