Mercury Barometer Air pressure is measured with an instrument called a ROM-uh-ter). barometer (buh One kind of barometer is a mercury barometer. Look at the mercury barometer on page 225. The mercury barometer was invented by an Italian scientist, Evangelista Torricelli (eh- van-jeh-LEE-stuh tor-ih-CHEL-ee). A mercury ba rometer is made of a glass tube filled with mer- cury. The tube is open at one end. The open end of the tube is placed in a container of mercury. Air pressure pushes down on the surface of the mer- cury in the container. The mercury is pushed up the tube. At sea level, air pressure can hold up a column of mercury 760 mm high. As the air pressure changes, the level of mercury in the tube rises or falls.