Galileo Thermometer

When it comes to thermometers we are spoiled for choice nowadays with everything from the tried and true mercury thermometers to cutting edge digital sensors. Italian astronomer and physicist Galileo made a number of significant discoveries, one of which was that temperature variations have an effect on how much a liquid expands and shrinks or its density. The Galileo thermometer, usually a glass tube or ball filled with liquid and glass baubles filled with liquid and each with a specific temperature medallion was developed in response to what he discovered.

The water inside the Galileo thermometer changes temperature along with the atmospheric temperature which causes the water to either expand or contract and alter its density. Some of the spheres will float when the water density changes, while others will sink.

The medallions are calibrated counterweights that are imprinted with a temperature reading. They are responsible for the spheres’ rising and falling. The weight of sinking spheres is more than the temperature, whereas the weight of floating spheres is less than the temperature. Depending on how the spheres are responding several techniques are used to determine the temperature. One sphere has the correct temperature reading on its medallion if it floats roughly in the middle of the floating and sinking sphere groups. If there isn’t a sphere floating in the middle of the top group of spheres and the bottom group of spheres the temperature can be calculated by averaging the readings from the lowest sphere in the top group and the highest sphere in the bottom group. When all the spheres float the temperature is below the lowest sphere. If all the spheres sink, the temperature is above 28°C or 84 degrees Fahrenheit.