Principle objective of this lecture is to present on Barometers. A Barometer measures air pressure. An Italian scientist named Torricelli built the first barometer in 1643. People still use barometers based on Torricelli’s design to measure air pressure. The atmosphere is the layers of air wrapped around the Earth. That air has a weight and presses against everything it touches as gravity pulls it to Earth. Barometers measure this pressure.