How To Read a Galileo Thermometer

How To Read a Galileo Thermometer

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A Galileo thermometer is one of the most attractive ways to read the temperature of your home. The colorful balls in the tube may look decorative, but if you know how to read them, it will tell how hot or cold it is.

Not sure how to read a Galileo thermometer? Follow these easy steps to using the colorful instrument so you can maximize its benefits beyond just aesthetics. It’s fun reading the temperature because it’s beautiful, functional, and easier than you think.

What is a Galileo Thermometer?

Detail of a galileo thermometer with white background

A Galileo thermometer, also known as a Galilean thermometer, is an instrument for determining the temperature of air or water. It is a closed glass tube with liquid inside. There are also small glass bulbs of different colors. 

The colored liquid in each bulb is mostly decoration. The density and weight of each metal tag are more critical since they measure the temperature of the surroundings. 

Temperature changes influence the liquid’s density, causing the colorful bulbs to sink and float.

The Galileo thermometer is a beautiful way to measure indoor temperature. You can check whether your HVAC system’s thermostat readings are accurate or not. You can also learn if your heater delivers the same performance in every room.

Is a Galileo Thermometer Accurate?

There is no such thing as a perfect thermometer. Like other thermometers, the Galileo thermometer’s accuracy depends on its location. It should be away from direct sunlight, cold spots, and heat sources.

The difference between the spheres also determines the accuracy of the thermometer. Ideally, these bubbles should have intervals of two degrees for accuracy. The higher the interval, the greater the possibility of error. 

If you want to measure temperature, but also monitor humidity levels in your home or RV, consider getting a temperature monitor.

How the Galileo Thermometer Works

It is essential to understand that the Galileo thermometer works on three physical principles. These are buoyancy, density, and gravity.


Buoyancy is the upward thrust of water as opposed to an object. Water exerts a force on the sinking or partially sinking object. 


Density is the mass for every unit of volume or just mass divided by volume. Simply put, it measures how tightly a substance is packed at a specific volume. 

As air warms up, the liquid also warms and gets less dense. As a result, the spheres rise to the top. But if the glass spheres have the same density as the liquid, they may float halfway.


Many overlook the role of gravity in the mechanism of the Galileo thermometer. It is the force of the Earth that pulls everything on the ground. The density of water and gravity battle to determine the spheres’ buoyancy.

What You Will Need to Follow This Tutorial

You only need three things to prepare before you can get accurate temperature readings for your Galileo thermometer:

  • Your Galileo thermometer.
  • Indoor hanging hook.
  • An environment with shade.

You can also let the Galileo thermometer stand on the tabletop instead of a hook. However, the temperature readings may not be accurate. The Galileo thermometer won’t contact hot or cold surfaces if you hang it somewhere spacious. The temperature reading will also not get affected by different objects. 

It’s also advisable to avoid placing it in direct sunlight. An environment with shade is vital for more precision. 

Step-By-Step Guide on How to Read a Galileo Thermometer

Reading a Galileo thermometer is simple if you understand how the metal medallions work. Here’s how. 

1. Choose a Large Galileo Thermometer

When learning how to read a Galileo thermometer, choose a larger one. Smaller instruments have glass balls with a big difference of 6 degrees Fahrenheit. And the greater the difference, the bigger the margin of error. 

The thermometer must contain liquid and glass spheres. These glass spheres not only make it a decorative instrument, but they also have the temperatures engraved. You’ll find the numbers on the metallic medallions hanging. 

The bubbles, bulbs, or spheres come in different colors. They also have different weights and sizes, although the densities are similar.

2. See How the Cluster of Spheres Floats and Sinks

Always observe how the spheres are positioned inside the vessel. Because of the principle of buoyancy, these colorful glass bubbles submerge in high temperatures and float when it’s cold. 

Objects with lesser density than their surroundings will float. Meanwhile, those with high density will automatically sink. 

There is also liquid inside each glass sphere. But it’s not a sensitive liquid like the clear one in the thermometer. The clear liquid in the thermometer contracts or expands depending on the ambient air. 

When the temperature falls, the liquid contracts and gets denser. Such a change in density causes the bubbles to rise. When it grows, the liquid expands, and the bubbles sink.  

3. Hang Your Galileo Thermometer

A Galileo thermometer uses different densities of liquids in glass bubbles to determine temperature

The accuracy of your thermometer depends on where you place it. The device works best in indoor locations instead of outdoors. But if you need to read outdoor temperatures, put it in a shaded area far from sunlight.

Keep the thermometer away from heat and cold spots when taking indoor temperatures. Avoid positioning your Galileo thermometer near HVAC vents, kitchen appliances, doors, and windows. 

Once you know where to position it, it’s time to find out how to arrange it. Hang the thermometer using a hook to catch the temperature of the air. Don’t let it touch the tabletop or your hand because it will warm up and give distorted temperature measurements. 

Note that the Galileo thermometer works best in an average temperature range of 64 to 8 degrees Fahrenheit. This condition is where they give the most accurate metrics. 

4. Place it in a Beaker for Water Temperature.

You can also measure the water temperature using a Galileo thermometer. Place the glass tube in a beaker with the liquid. Then, fill the container with warm or cold water or alcohol to determine the water temperature. 

Don’t use a Galileo thermometer to measure high water temperature increases. Make sure the water is only warmer than the room’s ambient temperature.

5. Wait for a Few Minutes

Leave your Galileo thermometer for a few minutes. Doing so will allow the colored glass spheres to float and sink within the attractive glass tubes. This movement depends on the density of the water. It contracts or expands depending on the ambient room current temperature.

Some bubbles will sink, while others will float. It’s also possible for all the spheres to float or sink.

6. Read the Tag in the Middle Sphere

Here’s the best-case scenario when learning how to read a Galileo thermometer. A group of colorful bubbles is sinking while the other cluster is floating. Then, there’s a single bubble in the middle. 

If your Galileo thermometer looks like this, read the tag on the medallion. The number engraved is the temperature.

7. Average the Highest and Lowest Spheres

Sometimes, there will be no single glass sphere in the middle. If there’s no bubble hanging alone, you will need to use your math skills. Find the average of the highest and lowest bulbs. You can only try this when one bubble with a metal tag hangs while the other sinks. 

Simply add the two numbers and divide by two to determine the temperature. For example, the sphere at the top might say 24, and the bulb at the bottom says 72. Their total is 96. Divide that by two, and you’ll get 48 degrees.

8. The Temperature is Low if They are All Floating

If all the clusters of bulbs or spheres are floating, the current temperature is colder than the highest medallion tag. You won’t get an accurate reading because it has gone beyond the range.

Remember that all the spheres float on top of the glass vessel in low temperatures. That’s because the glass gets denser than the bulbs. 

9. The Temperature is High if They are All Sinking

The temperature has reached higher than it can read if all the glass bubbles sank. This appearance indicates that your weather conditions are too hot. 

As the liquid water or alcohol heats up in your thermometer, it gets less dense than the bulbs. The outcome is a whole cluster of bulbs submerged in the liquid. 

The medallion tag on the lowest sphere is much lower than the actual temperature. 

10. Remember that Galileo Thermometers are Not Precise

Galileo thermometer temperature bubbles

Aside from their narrow air temperature range, Galileo thermometers cannot determine the precise air temperature of your surroundings. Two-degree increments can offer more accuracy in temperature readings.

Or just get a more accurate device that senses temperature and humidity levels.

Still, the Galileo thermometer is an aesthetically pleasing way to determine your weather conditions. It’s colorful, fun, and informative. 

In Conclusion

Did you enjoy this tutorial on how to read a Galileo thermometer? Have you tried using yours to check the temperature? 

Learning how to use this instrument helps optimize your home’s comfort levels. You’ll realize that the Galileo thermometer is not just a decorative piece you can hang inside your space. It adds fun and color to the mundane act of checking how hot or cold it is.

Leave your thoughts about the Galileo thermometer in the comments below, and we’ll be happy to read them. And if you enjoyed reading this, share it with your weather enthusiast friends. For more awesome tips and guides, check out our best indoor hygrometers.

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