I love nerdy science stuff.

And just like anyone else, I like to surround myself with the things I love.

The result is that my home decor is what one might call science chic. My dining and living rooms are natural history inspired with fossils, minerals, and other natural wonder objects. The family room is more physics and scientific instrument inspired. I liken it to living in a museum which I think is awesome.

(See related: 5 reasons a kaleidoscope isn’t just for kids anymore and why you should collect them)

galileo thermometer with wooden frame

My Galileo thermometer

In my family room, one of my beloved objects is my Galileo thermometer. It is approximately 14.5 inches tall with a stand made of wood. The glass bulbs contain various saturated colors. From the bulbs hang golden metallic tags. In my opinion, the clean lines make it rather striking. You can see it on the right and let me know what you think.

Gazing upon it makes me happy. Guess it doesn’t take much, huh? They say it is the simple things in life that make us happy. Actually, it isn’t that simple. It gives me joy because not only is it beautiful, but it also reminds me of the elegance of science and the natural world. It is inspiring and humbling all at the same time.

I feel like that about a lot of scientific instruments. If you share my interest in scientific instrumentation, I encourage you to read my article If you like the Large Hadron Collider, then you’ll like these.

Inspired by my joy, I wanted to share the secrets behind the Galileo thermometer in this article. When was it created? How does it work? How is it made? Let’s take a look.


Who was Galileo?

Galileo Galilei was an Italian scientist and scholar. He was born in 1564 in Pisa -and yes the famous tower had been leaning for several hundred years by then. He was a pioneer in scientific discovery as well as in the methods he used. It is odd that we refer to him by his first name as most famous people of history are often referred to by their last name.

galileo galilei

You are most likely familiar with him because of his use of telescopes on the night sky. Perhaps you have heard about his scuffle with the Catholic church surrounding his support of the Copernican theory (you know, where the Earth orbits the Sun instead of vice versa).

I do not feel obliged to believe that the same God who has endowed us with senses, reason and intellect has intended us to forgo their use.  


-Galileo Galilei

He did not invent the Galileo thermometer. However, he did discover the property that drives its behavior. That the density of a liquid changes with temperature.

He did invent the thermoscope which merely shows when a temperature has changed. It doesn’t include the measurement of how much the temperature has changed using a scale of measure.


Why is it called the Galileo thermometer if he didn’t invent it?

Because he inspired it. Galileo discovered that the density of liquids would change predictably under temperature fluctuations. As stated above, he also created a thermoscope. Without these discoveries, the Galileo thermometer wouldn’t exist.

It was his student and others that ran with the idea and created the Galileo thermometer. By carefully calibrating the suspended bulbs with the surrounding liquid, it could function as a thermometer.


How is the Galileo thermometer made?

galileo thermometer closeupThe thermometer consists of a clear liquid, usually ethanol, inside an enclosed glass column. Submerged in the ethanol are several glass bulbs with suspended weights hanging below it. Pretty simple actually.

What is special about the bulbs?

Not much. Each glass bulb holds the same amount of liquid inside it. Because of the aberration of the glass cylinder they may not look the same size, but they are. The liquid is colored for purely decorative purposes.

The magic is in the suspended weights attached to each bulb. Each weight has a slightly different and carefully calibrated mass. The weights are marked with a specific temperature. The temperature where density equilibrium is attained between the bulb/weight and the ethanol.

The lightest weights are at the top of the column because their low density causes them to float to the top. The heaviest weights are at the bottom because their density causes them to sink.


How does the Galileo thermometer work?

As the room temperature changes, the temperature of the ethanol changes. When the temperature of the ethanol changes, so does its volume. It will expand if it gets warmer and conversely it will contract if it gets colder.

As the volume of the ethanol changes, so does its density. Anything in the liquid with a higher density will sink while those with lower densities will float.  If something has the exact same density, it will neither sink nor float and will remain suspended. The bulbs will move up or down in the column corresponding with the changing density of the ethanol.

What is density?

Simply put,

Density = Mass / Volume

I can’t say density without thinking of Back to the Future and George McFly telling Lorraine that he is her density. Poor guy, I felt so uncomfortable for him!

Density is how much of something is packed into a specific volume of space. You know the joke about what weighs more? A pound of feathers or a pound of rocks. Well, they may have the same mass, but they have different densities because they take up different amounts of space. The rocks have a higher density.

Put another way, a brick of steel will sink. A boat made of steel will float. Why? The density is either heavier or lighter than the water displaced. A brick is small and weighs a lot so it has a high density, higher than water density. A boat is heavy but displaces a lot of water; so the boat density is lower than the water density it displaces. Thus it floats.

On a related note, there is a funny scientific legend surrounding volume and water displacement. Ancient Greek Archimedes was tasked with identifying if a golden crown had been diluted with silver. Pondering the task, he lowered himself in the bath. He noticed that the water level rose as his body submerged. He then realized that was the key to discerning if the crown contained silver or was pure gold. Gold and silver have different densities so given a fixed mass, the volume displaced with be different. Legend has it that Archimedes was so excited he ran down the street naked shouting Eureka! Eureka! which means “I found it!, I found it!”


Reading the temperature

If there is a bulb suspended in the middle of the column, that weight marked on that bulb is the temperature. If there is  a group of floating bulbs and a group of sunken bulbs, the temperature is the weight assigned to the lowest floating bulb.

Since gases and liquids are poor conductors of heat, Galileo thermometers are slow reacting. So, if you put it outside on a freezing cold day, it would still take a while for the ethanol to cool down. For practical purposes, this isn’t scientifically precise. Although, I think the graceful movement adds to the appearance.

You may also notice that it has a limited number of bulbs. Mine has 7 bulbs with a range from 60 to 84 degrees fahrenheit. Just enough to cover the comfortable room temperature range. But for practical purposes, it has limited applications.


The Galileo thermometer in time-lapse action


Does it float your boat?

If you have ever jumped into a lake or other outside body of water, you may have noticed that the water on the surface is warmer than the deeper water. That was your informal experiment with temperature and water density. Didn’t realize you were doing science, did you?

Are you fascinated with the elegance of the laws of nature? Remember all the cool experiments in high school physics class?

I have deep faith that the principle of the universe will be beautiful and simple.


-Albert Einstein

If you haven’t noticed, I get quite romantic about the mystery of the cosmos. My curiosity will never end. Granted, much of what is simple to Albert Einstein is likely beyond my grasp of understanding. However, I do marvel at the simplicity of E=mc².

What are your thoughts? Fascinating? Boring? This is the world we live in. Constantly surrounded by the laws of physics even if we don’t realize or understand. They are always there.

Let me know your perspective in the comments.



Density from Vision Learning

Fact or Fiction?: Archimedes Coined the Term “Eureka!” in the Bath from Scientific American

Galileo from Biography

Galileo Thermometer from Real World Physics Problems

‘Galileo thermometers’ said not Galileo’s from UPI

Galileo thermometer time lapse from YouTube

Science Quotes from Lock Haven University

The Galileo Thermometer – Beautiful Science from Kuriositas

The Mystery of the Galileo Thermometer from Headline Science Now

The Perimeter of Ignorance from Natural History Magazine

Wikipedia contributors. “Galileo thermometer.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 31 May. 2015. Web. 6 Oct. 2015.