What Is A Galileo Thermometer And How Does It Work?

Measure what is measurable and make measurable what is not so - Galileo Galilei 

It’s easy to forget that we are living in an age in which science is as fundamental to everyday life as the air that we breathe.

While we now take science for granted and defer to the wisdom that it imparts and the theories that guide us further down the path to enlightenment, it’s easy to forget that we weren’t always so ready to believe.

What Is A Galileo Thermometer And How Does It Work

Less than half a millennia ago, the idea that one day we would all accept scientific principles and theory as our collective guiding light was widely regarded as being heresy.

That heresy formed the basis of the scientific renaissance and was, partly responsible, for helping to fuel the insatiable curiosity that drove it forward and helped dispel the last of the lingering clouds of the Dark Ages.

And chief among those heretics was the man whose work would form the basis for multiple scientific disciplines for centuries to come, Galileo Galilei.

Who Was Galileo? 

Galileo was far more than a lyric in a Queen song. Born in Italy in 1564, he is often described as being a mathematical and scientific polymath and is commonly regarded as being the father of both modern physics and modern science. 

An astronomer, physicist, and engineer, Galileo famously studied gravity, velocity, projectile motion inertia, and the principle of relativity, while also describing the properties of pendulums and hydrostatic balance, which is the study of fluid mechanics and the ways in which fluids, when immersed in another fluid, react with one another. 

A noted champion of Nicholas Copernicus (who first suggested the idea of heliocentrism, or as it’s more commonly known, the later proven idea that the Earth revolves around the sun), it was Galileo’s support of Copernicus and his criticism of the papal clergy that led to him being tried by the Inquisition. 

Found to be “vehemently suspected” of being a heretic, Galileo was forced to recant his support of, and belief in, Copernicus’ model and was placed under house arrest for the rest of his life.

While more famous for being a physicist and astronomer, Galileo also used his furious intellect to develop a number of different compasses that were used by the military, spent a great deal of his working life attempting to perfect and further develop the telescope, and as a result of his continuing interest in, and fascination with fluid mechanics, also invented the thermoscope.

Galileo’s early thermoscope was the basis for and is still used as a working model, for the widely used temperature measuring device that has come to be known as a Galileo Thermometer.

The Galileo Thermometer

While based on the original model and design of Galileo’s Thermoscope, the modern Galileo Thermometer has very little in common with, both in terms of functionality and design, the Thermoscope. 

As much a sought-after and desirable home decoration as well as being an incredibly effective and efficient way of measuring temperature, the Galileo thermometer is a sealed, liquid-filled glass tube in which a number of glass bulbs each filled with different liquids float.

Each of these bulbs has a metal tag, upon which a number that indicates a temperature reading, attached to it, and rises and falls according to fluctuations in, and the rise or fall of, the temperature of the air around the thermometer.

How It Works

The metal discs attached to the bottom of each of the glass bulbs that indicate the temperature are designed to act as perfectly designed and engineered counterweights that act as a weighted balance for the bulb that they are attached to.

While the bulbs vary in size and contain a different amount of colored liquid (the fluid inside the bulbs often contains food dye and alcohol), they are finely adjusted so that they each have roughly the same density.

The crucial component that allows a Galileo thermometer to work are the differently weighted and sized metal tags that are attached to the bulbs. 

As the air surrounding the thermometer increases or decreases in temperature,  the temperature of the water inside the thermometer also increases and decreases, which causes it either expand, as it gets warmer, or contract, as it cools down.

As the temperature of the water fluctuates, so does its density, which in direct opposition to the way the temperature affects it, decreases, as the density rises and increases as the density gets lower. This causes the glass bubbles within the thermometer to rise toward the surface or sink according to the density of the water within the thermometer.

The thermometer works, as did Galileo’s thermoscope, according to the principle of buoyancy. This means that the bubbles inside the thermometer will rise or sink according to their specific weight.

The bubbles that are heavier, or have a greater density than the water that surrounds them will sink, and the bubbles that weigh less, or have a smaller density than the water that envelopes them, will rise toward the surface of the thermometer.  

As the thermometer works in the same way that Galileo’s original thermoscope did, it was named in honor of, and after, the Italian scientist. 

Heating Up And Cooling Down - How To Read A Galileo Thermometer

Primarily designed to give a temperature reading between sixty and ninety degrees Fahrenheit, and made to be used as a means of reading interior temperatures, it is incredibly easy to read a Galileo thermometer.

The first thing to remember, and to note, is that you need to ignore all of the glass bulbs that have sunk to the bottom of the thermometer.

In order to read the temperature, you only need to focus on the bulbs that are floating, and in particular, the lowest bulb, or the glass bulb that is floating closest to, but not sitting on, the bottom of the thermometer.

The disc attached to the lowest floating glass bulb will provide a rough indication of the ambient temperature of the room that the thermometer is in. 

While they’re not a precise way of measuring the temperature of a room, or as accurate as mercury or digital thermometer, Galileo thermometers are nonetheless, a scientific curiosity that are meant to be enjoyed and celebrate the life and numerous achievements of the father of modern science, Galileo Galilei. 

About the Author Marvin J. Snyder

I'm the research analyzer and data interpretation here at Weather Station Lab. I test various weather stations and share my conclusion here. Since my childhood, I had a passion towards weather and I'm always fascinated by that. Eventually, I pursued Ph.D. in Atmospheric Science from the University of Arizona. I hope my contribution will help you to know more about weather stations. Read more about us, here