When it comes to weather forecasts you probably already know that a barometer can help. It can show if the atmospheric pressure is falling or rising which is very helpful for predicting the kind of weather you are likely to experience. However, how does a barometer work exactly? There are several types of barometers, but the basic way they all function is the same.
First of all, we should note that the atmospheric pressure can change in a very short period of time. This is due to different weather fronts moving from one place to another. This is why it is important to have a local barometer, so that you are not misled by what might be happening in other places far away.
There are a couple of different ways that a barometer can measure the air pressure. The most common type is the mercury barometer which was invented by Evangelista Torricelli in 1643. It has a glass dish that is filled with mercury and an attached tube that rises and falls with air pressure changes.
A similar type of barometer is the aneroid or Vidie barometer which was invented in 1844 by Lucien Vidi. This is liquidless and works thanks to a hermetic metal box that has most of the air pumped out of it, called an aneroid capsule. During pressure changes this capsule expands or contracts which in turn pushes mechanical levers that control the needle of the barometer.