The thermometer was invented by Galileo Galilei in 1593. His thermometer consisted of water in a glass bulb; the water moved up and down the bulb as the temperature changed.
The sealed thermometer was invented in 1641 by the Grand Duke Ferdinand II. He used a glass tube containing alcohol, which freezes well below the freezing point of water (alcohol freezes at -175°F=-115°C). He sealed the tube to exclude the influence of air pressure.
Mercury was later substituted for the alcohol, and then Daniel Gabriel Fahrenheit (1686-1736), a German physicist, used mercury plus a chemical solution that kept the mercury from sticking to the tube of the thermometer (in 1714). Fahrenheit also expanded the thermometer's scale (in 1724); on his scale, the temperature of boiling water is 212°F and the freezing point of water is 32°F
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