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Galileo Thermometers


Galileo at age 38. Every substance has the property of 'mass', which is the basic physical presence of matter. Matter occupies space. A physical mass contained within a physical space produces the physical property of 'density'. For practical purposes, we define density as the mass of material contained within a specific unitary volume, usually as grams per cubic centimeter. The density of a material is a reflection of the energy contained by the molecules that compose the material. Molecular energy is exhibited in molecules by various vibrational motions. The more energy the molecules contain, the more they vibrate. The higher the temperature, the more the molecules vibrate and bump into each other. This tends to push teh molecules apart so that fewer of them occupy the same volume of space as the temperature increases.

Thus the mass of any material contained within a unitary volume of space tends to decrease as the temperature increases. Therefore density is inversely proportional to temperature; as temperature increases, the density of materials decreases. Each different material exhibits its 'energy behaviour' in its own unique way. This can be used to correlate the density of a material with its temperature. A Galileo thermometer is constructed using small glass spheres to make a series of floating environments within a larger tube that is usually filled with water. Each sphere contains a specific amount of water and air or another liquid and air, and is tagged with a precisely calibratedcounterweight.

The counterweightis marked with a specific temperature. Each sphere thus has a specific density at a specific temperature. The spheres float within the primary liquid at a level determined by the difference in their densities. Because each of the spheres changes density with temperature at a different rate, the difference between the densities of the two materials decreases in a predictable manner. The level at which any particular sphere floats within the primary liquid changes accordingly. In this way, the temperature is clearly indicated by the sphere floating at the lowest level within the primary liquid.

About the Author


Richard M. J. RenneboogRichard M. J. Renneboog, MS
Richard M. J. Renneboog is an independent private technical consultant and writer in both chemical and computer applications. Endeavors have included preparation of scripts for instructional and promotional video, corporate website design, curriculum development for training in advanced composites technology, and development.

Further Reading
A History of the Thermometer and Its Use in Meteorology
by W. E. Knowles Middleton


Related Web Links
About Galileo
by The Galileo Project

About Temperature
by Project Skymath





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