How a Galileo Barometer Works

In addition to being useful tools to predict near-term weather, Galileo barometers can be used as decorations for the living rooms of the scientific-minded. They provide a visual representation of atmospheric pressure based on the water level in an open tube.


Storms usually follow low-pressure fronts.

The Galileo barometer is based on a single piece of glass and a fluid, usually distilled water.  The glass has an area dedicated to housing a reservoir of fluid and a thin, upward-facing spout that is open to the atmosphere.

The water is often dyed so it can be seen from a distance. 


To fill the reservoir, use a syringe to overcome the vacuum seal created at the point where the spout connects with the reservoir.  The device is usually turned upside down and filled one syringe-full at a time until the fluid is approximately halfway up the spout.

There must be room for the fluid level to fluctuate in both directions as the atmospheric pressure changes. 


When a low-pressure weather system approaches, the weight of the air pressing on the open end of the spout decreases, allowing the water level to rise.  Conversely, when a high-pressure system moves in, it will push the water level down.

A scale can be printed on the spout corresponding to the inches of mercury, normally between 28 and 32 inches. 

About the Author

A professional travel writer since April 2010, Doug Leenhouts has written for world66.com and slowtrav.com. He has a Bachelor of Science in management information systems from the Worcester Polytechnic Institute and three years of service in a consulting firm.

Photo Credits

  • storm weather image by Galyna Andrushko from Fotolia.com