Barometers are instruments that measure atmospheric pressure as an indication of weather.
Most often used are the mercury barometer and the aneroid barometer. A change in height of the column of mercury indicates a change in atmospheric pressure. In an aneroid barometer, a shallow cylindrical metal box containing a partial vacuum expands or contracts in response to changes in pressure. The movements of the box sides are transferred to a pointer and scale via a chain of levers. For further information, please refer to any encyclopaedia in your school or public library.