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Thermometers: For Measuring Temperature

It may seem obvious to say that thermometers are designed for measuring temperature. Thermometers surround us in our everyday lives. We have thermometers hanging outside our windows so that we can get an idea of what it is like outside. We have thermometers indoors, and on our thermostats. We are treated to thermometer readings on radio, television and the internet. We use thermometers to measure body temperature. There are even thermometers on our fish tanks, or that we stick into turkey roasts and ovens. There is a thermometer on your car's engine, in refrigerators and freezers. Modern life would be just about impossible without a way to measure heat levels, and then adjust for them.

Keep in mind that a thermometer does not measure the amount of heat; it measures its intensity. For example there would not be much heat on the head of a lit matchstick. There would be much more heat on a bonfire on a beach. However, the intensity of the heat of each might be just the same. To find out how much heat is within a system would require taking the temperature and applying it to the volume and mass of the system.

It was not so long ago that thermometers were unknown. It was not until Galileo, Santorio, and Gianfrancesco Sagredo began experimenting with something they called the thermoscope in the early 1600s that people could put any quantification at all on temperature other than the general, hot, cold, or middling warm.1 The instrument they developed was crude and relied on air or gas in a tube, similar in manufacture to a barometer. Yet it was a large step forward.

Daniel Gabriel Fahrenheit took the first real step in coming up with accurate thermometers based on an objective scale. He was the inventor of the mercury thermometer. Anders Celsius created an even better scale that used the freezing and boiling points of water. Finally, Lord Kelvin, William Thomson came up with an absolute scale that took into account the very lowest temperature possible in the universe.

The way thermometers work is actually quite simple. Classically, thermometers have a bulb at the base of a long glass tube. The bulb is filled with some kind of medium, usually red tinted alcohol or mercury. The substance expands when it is warm and contracts when it is cold. It has nowhere to expand to other than up the tube. Knowing how far the mercury will expand in the tube at various temperatures, engineers have made marks beside the glass tube indicating a designated degree when the mercury should expand or contract to that point.2

A spring thermometer works on a similar principle, only it uses a coiled spring of metal that will expand in the heat and contract in its absence. The coil is attached to a pointer that is pushed or pulled as the spring moves. Again the expected place the pointer will indicate on a dial at particular temperatures is marked on its face. This device is used in many thermostats also. It, however, is generally less accurate than a bulb thermometer.

Thermometer is a word that was made from two other words, thermo meaning heat, and meter meaning measure.

<-- Lord Kelvin and His Scale | Temperature Conversion Tool -->


  1. Referencing article originally at: http://galileo.rice.edu/sci/instruments/thermometer.html - Galileo Project
  2. Energy Quest



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