Which Italian physicist invented the first mercury barometer in 1643?

Evangelista Torricelli invented the first mercury barometer in 1643. The instrument used a long glass tube closed at one end and filled with mercury, which was then inverted into a dish of mercury. The column fell partway, leaving a near-vacuum above it, while atmospheric pressure supported the mercury below.

Torricelli’s experiment showed that air has weight and exerts pressure. The height of the mercury column varied with changing atmospheric conditions, creating the foundation of the barometer and modern atmospheric-pressure measurement. Mercury was especially practical because its high density allowed a manageable tube roughly a metre long.

Torricelli had been a student and assistant of Galileo Galilei, but the barometer was his own major contribution. Robert Boyle later helped develop the study of gases, while Blaise Pascal used related experiments to investigate how atmospheric pressure changes with altitude. Torricelli’s work also helped overturn older assumptions about nature’s supposed horror of a vacuum.