Have you seen one of those glass tubes with different colored glass spheres floating in a clear liquid? Ever wondered what it did or what it was for? What may look like a really cool piece of modern-day art is actually a very old device used to tell the temperature. It’s a Galileo thermometer.
A Galileo glass thermometer is based on Galileo Galilee’s discovery that the density of fluids will expand and contrast with temperature. The thermometer is actually a hand-blown glass container. Inside the container are a series of spheres, filled with liquid. These glass spheres move up and down to indicate changes in ambient temperature.
So, how exactly does a Galileo thermometer work? On each of the glass spheres, you’ll notice a medallion. This medallion is imprinted with a temperature reading. The medallions are an important part of the thermometer because they are carefully calibrated counterweights. The weight of each medallion is a little bit different from the other medallions in the container. It’s the medallions that actually are rising or sinking in relation to the water temperature. But because the medallions are attached to a glass sphere, it seems like the spheres are moving in relation to the temperature.
When the glass spheres are put in the Galileo glass thermometer, they respond to fluid forces – an upward push from buoyancy, and a downward pull from gravity. As the air temperature outside the thermometer changes, the water temperature changes accordingly. With the change in temperature, the water either expands or contracts, changing its density. And as the density changes, some of the spheres will float to the top, others will sink to the bottom.
The spheres that sink to the bottom are heavier than the actual temperature – the spheres that float to the top are lighter than the actual temperature, but the sphere that is lowest floating in the top group reflects the actual temperature. You merely need to read the medallion on that sphere to have the temperature.
Galileo glass thermometers are fascinating devices. It’s amazing to watch these thermometers in action and contemplate the scientific theory behind them. What’s even more amazing is realizing that this theory is actually hundreds of years old.
Galileo thermometers make wonderful decorative pieces in a home or office. You can find a variety of thermometers – hanging, on stands, or encased. Part of the fun of owning a Galileo glass thermometer is explaining how it works to all the admirers. It’s sure to be a crowd pleaser.
