The Galileo Thermometer: Beauty, Function, and Math
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The Galileo Thermometer: Beauty, Function, and Math

The Galileo Thermometer is more than just a pretty tabletop novelty, -it is a surprisingly accurate temperature measuring tool and uses some fairly sophisticated principles of physics.

Today, it is mostly a curious ornament for your home or cubicle desk at work, but this odd-looking glass tube with the colored spheres is a serious thermometer and surprisingly accurate.

Thermoscope, invented by Galileo Galilei

Galileo portrait

Galileo (his full name is “Galileo di Vincenzo Bonaiuti de’ Galilei”) was the Italian inventor who created this device in the 1600's: a liquid-filled vertical glass tube that contains precision-weighted spheres (today, of either colored water or alcohol, and mostly for decoration purposes,) each calibrated to a specific density. The liquid-filled tube is sensitive to the ambient air on the outside, and since temperature and density of liquids are uniquely intertwined, this device responds precisely to this change.

Image via Wikipedia

As the density of the flotation liquid changes in direct relation to the temperature, the weighted bulbs will move up and down seeking an equilibrium state--a tool for indicating temperature. Galileo more or less stated " . . . that the laws of the natural world are mathematical," and this accurate device shows a relationship in keeping with this statement.

Metal Counterweight Tags Attached in the Galileo Thermometer

Each sphere in these modern productions is adored with a small ringlet and labeled metal tab, indicating a temperature. The tags serve as counterweights for the floating sphere because the hand-blown glass spheres cannot possibly be made the same thickness, mass, size, etc.

What happens is that each sphere is hand-adjusted to attain neutral buoyancy at the target ambient water temperature. Subject to two natural forces, gravity and buoyancy, this sealed liquid-filled glass tube seeks to maintain the same temperature as the air. This in turn is relayed to the spheres and if a sphere is denser than the specific gravity dictated by the water temperature, it sinks.

Galileo thermometer

 Image source

Changes in air temperature are realized quickly, and the glass spheres respond in seconds or minutes. Sometimes, surprisingly quickly! As a glass sphere moves up or down, it bumps and glides past its neighbors.

Galileo thermometer

Image Source

 If any sphere that is less-dense than the changing current specific gravity of the water at temperature, it will rise towards the top of the glass tube. The sphere that is closest to the actual current temperature of the liquid in the sealed tube (which strives to be the same temperature as the ambient air surrounding it) is ‘neutral’; it sinks as much as it rises. The forces of gravity and buoyancy are equalized:  thus the specific sphere is stationed at or near the middle of the glass tube and reveals the actual temperature.

It the glass sphere is slightly higher than ‘middle,’ then the temperature is somewhere between its tagged value and the next highest glass sphere below it. Some Galileo thermometers have just five glass spheres, others have more spheres for a greater range of temperature indication. I have a Galileo thermometer that has eleven glass spheres.

Galileo thermometer

 Image Source

Broken Tip on a Modern Galileo Thermometer

glass Galileo thermometer with a broken tip

Image Source

Sadly, these modern versions, while exceedingly beautiful, are still as fragile and quite prone to breakage as seen here in this above image. But these devices are common and of course, replaceable. Many scientific retailer stores and even ‘big box stores’ often have them, especially around Christmastime. As you can see, the glass spheres even look ‘Christmassy.’

The Galileo Six

spheres from a broken Galileo thermometer

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Too bad only six glass bulbs are shown here, for if there were seven glass bulbs we could call this “The Galileo Seven” which to us Star Trek fans out there, means something.

Class STAR TREK Collector plate

Image via Wikipedia

The Galileo Seven” was the name of a classic Star Trek episode and “Galileo” the name of the doomed U.S.S. Enterprise shuttlecraft in the episode. I wanted to mention all of this as the author of this image cites that this Galileo thermometer that became broken was a gift from his sister and as such, it seems fitting to remember it here again.

After the breakage and the fluid runs out, the device is effectively destroyed. There is no fixing it. But at least you can be left with some very interesting objets trouvés: colored water-filled glass spheres for a display in clear vase or bowl centerpiece.

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