- The earliest temperature-measuring devices were used by the Greeks around the first century B.C. to perform simple experiments that noted changes in temperature.
- Though credited to at least four different scientists, Galileo Galilei is generally acknowledged to have created the thermoscope in 1592. The thermoscope is a large glass bulb with a long, narrow, open neck inverted over a vessel of colored water or alcohol. When air was driven into the neck, the liquid rose into the tube, registering changes to the temperature of the liquid in the bulb.
- In 1611, Sanctorius Sanctorius (or Sanctorio Sanctorio) improved on Galileo's device by adding a scale to measure the changes in temperature. By the early 18th century, some 35 different scales had come into use in various attempts to calibrate the thermometer readings.
- One of the few scales to survive was invented by German physicist Daniel Gabriel Fahrenheit, who became famous in the years 1700 to 1730 for the quality and accuracy of his mercury thermometers. His scale used the melting point of ice (32) and blood heat (96) as its two fixed points for calibration.
- From the earliest days, scientists were aware that thermometers are influenced by atmospheric pressure and sought ways to overcome its effects. In 1742, Swedish astronomer Anders Celsius produced the first centigrade scale, which used as its fixed points the temperature attained when the thermometer bulb was immersed in melting snow (100) and when it was immersed in water boiling at a particular barometric reading (0). The scale was eventually reversed and remains in use that way today.
- Thermometers are used to measure much more than air or water temperatures, which has led to a variety of thermometers that use different scales, such as Rankin and Kelvin, to compensate for various factors affecting the readings. Currently, the most common and familiar thermometers use liquid mercury in hermetically sealed tubes filled with nitrogen gas.
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