The document summarizes the invention and history of the barometer. It describes how Evangelista Torricelli is credited with inventing the mercury barometer in 1643, though others may have developed early versions. A barometer measures atmospheric pressure and weather forecasters, pilots, and divers utilize barometers. The document then explains how mercury and aneroid barometers function, noting that mercury barometers work by balancing the mercury's weight with air pressure.