We’ve Seen It
with Our Own Eyes
Thermometers have been around in something like their modern form since the first mercury thermometer of Gabriel Fahrenheit, in 1724. There are many stories about the origin of the Fahrenheit temperature scale, but one is simply that 0°F was the coldest temperature that Fahrenheit experienced in the winter of 1708–1709, and 100°F was his own body temperature. The scale puts the melting and boiling points of water at the somewhat awkward temperatures of 32°F and 212°F, respectively. We in the United States tend to think of the metric system as some newfangled thing, but the Celsius scale is no younger than the Fahrenheit scale. Fresh water melts and boils at 0°C and 100°C on the Celsius scale.
The very first temperature measurements might not have been easily comparable with each other, while the temperature scales were being defined. But the modern definition of the Fahrenheit scale was chosen just a few years after Fahrenheit’s death in 1739. A mercury thermometer is still considered a good way to measure temperature today.
Temperature is a relatively easy physical quantity to calibrate, because common substances like water have precisely stable