What instrument did Evangelista Torricelli invent to measure atmospheric pressure?

Evangelista Torricelli invented the mercury barometer to measure atmospheric pressure.

In 1643, the Italian physicist filled a glass tube with mercury, inverted it into a mercury reservoir, and observed that the column did not empty completely. The surrounding air pressed on the reservoir and supported the mercury column, leaving a vacuum at the top of the tube. Changes in column height revealed changes in atmospheric pressure.

Torricelli’s experiment also demonstrated that air has weight and helped establish the physical reality of a vacuum. At standard pressure, the mercury column is about 760 millimetres high, a value that became the basis of the unit torr.

A mercury barometer is different from an aneroid barometer, which uses a sealed flexible metal chamber. Anemometers measure wind speed, hygrometers measure humidity, and rain gauges measure precipitation.