What is Galileo Thermometer and How to Read it?


If measuring the temperature was an art, the Galileo thermometer would be the Picasso of it because no other instrument measures the temperature more magnificently than the Galileo thermometer.

what is galileo thermometer and how to read it

This is completely unlike your regular thermometers that use substances like mercury as the central component of measurement. The design and functionality are much more sophisticated than a regular mercury thermometer that expands or contracts at the command of the heat applied upon it inside a glass tube.

The composition of the Galileo thermometer consists of glass bulbs with colored liquids in it, which are used to mark the distinction.

In this article, we will explore all the key aspects of a Galileo Thermometer, from the comprehensive composition of the framework to the operation that allows us to measure the temperature via the thermometer and the method of reading the thermometer.

What is a Galileo Thermometer?

Galileo thermometer is a type of thermometer that consists of a liquid enclosed within a sealed glass vessel among several other glass containers of different densities. This apparatus is responsible for measuring the temperature.

The varying density of the containers inside the cylinder is the key feature of measurement via a Galileo thermometer. The containers have the density labeled against it, and they soar up or fall in proportion to their respective density when the cylindrical design is engulfed in liquid as the temperature changes.

How does a Galileo Thermometer work?

The Galileo thermometer is based on the principle of buoyancy which is the foundational law that probes the device to work. Buoyancy is the ability of some object to float in a liquid, notably water. It assesses what object may float in a liquid and what object may sink in.

Such abilities allow people to make things like steel boats that float in the water while the steel bar sinks deep. As I have mentioned, the principle of buoyancy is fundamental in the functioning of the Galileo Thermometer as the same principle is applied here to determine the temperature of the object.

The main determinant of the temperature of an object we need to measure is its density relative to the liquid's density. The densities of both are considered for determining the temperature. If the object has more density than the liquid, it sinks as the object is heavier than the liquid. On the other hand, if the object has less density than the water, it floats in the water.

  • For instance, if the bulb with 25 degrees Celsius as the label will have less density than the liquid in which it is submerged at the same temperature, prompting it to float. Simultaneously, the object of 24 degrees Celsius will have more density than the liquid, and it will sink to the bottom.
  • Each bulb has a metal tag attached at the bottom of it that denotes its temperature, and the tagging is what allows you to compute the temperature of the object. The tags have different weights, marking a clear distinction.
  • Though the bulbs may have different kinds of shape and size, and the liquids are of different colors with no apparent coding, they are adjusted so that the density of each ends up being the same.
  • These bulbs are just for pretense, and to make the clear-cut distinction, the tags have different densities, and the respective density is written on the tag.
  • These bulbs are just for pretense, and to make the clear-cut distinction, the tags have different densities, and the respective density is written on the tag.

The theoretical working of the Galileo thermometer is the same as other thermometers like Indoor Outdoor Thermometer. The heat is applied upon the device, and based on the resulting temperature, the liquid expands or contracts.

When the temperature of the ambient liquid is increased or decreased, the temperature of the glass bulbs will have a proportionate effect; that is, the temperature of the glass bulbs will too adjust as per the ambient temperature.

How to Read a Galileo Thermometer

  • To read the temperature on a Galileo thermometer, you have to look at the lowest-lying bulb.
  • The bulbs that have sunk to the bottom have no role to play in the computation of the temperature. Thus, no special attention should be paid to them. 
  • The center of our observation should be the bulbs that are still floating.
  • If a bulb is absent in the space between the soaring and sinking bulbs, the temperature of the lowest bulb should be taken into account. That's it.


The utmost beauty of measuring the temperature via the Galileo thermometer is unbound. While the enhancement of technology since the advent of this invention allows us to measure the temperature of various things without the elaborate design and unnumbered efforts, this traditional way of measuring the temperature remains a magnificent method.

You may not find this method much in use, but you will be in much awe of the procedure itself once you the hang of its mechanism.

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About the Author


I am Tim, a weather enthusiast who loves to watch hurricanes and all other harsh weather conditions. I studied B.Sc(Meteorology) at the University of Miami. With excellent knowledge of Weather Forecasting, Meteorology, and Environmental Science, I am currently working in San Francisco as a Meteorologist. Also, I am a member of The Weather Channel and AccuWeather. In this blog, I will write a detailed review of Weather instruments that you need for survival and other activities.