This is a picture of the Admiral Fitzroy Barometer first introduced in 1860. The actual length of the barometer is about 3.5 feet. Find out more about air pressure . Measuring Pressure Based on a principle developed by Evangelista Torricelli in 1643, the Mercurial Barometer is an instrument used for measuring the change in atmospheric pressure. It uses a long glass tube, open at one end and closed at the other.
Air pressure is measured by observing the height of the column of mercury in the tube.
At sea level, air pressure will push on the mercury at the open end and support a column of mercury about 30 inches high. If you used water instead of mercury, you would need a glass tube over 30 feet in length. Control the Weather To see how weather and pressure are linked, move your mouse over the scale lines on the barometer to the left and observe what happens to the picture above. Narrow-neck glass bottle. Instructions Insert a drinking straw into the bottle.