"How cold is it?" If you check the weather report, the answer will probably be in Celsius because most countries use the metric system and the Celsius scale. The U.S. is the only major country to use mainly the imperial system and Fahrenheit.

So, how did we get two systems? Well, back in the early 1700s, there wasn't a reliable system for measuring temperature. A German scientist named Fahrenheit was fascinated with thermometers. He worked to make them reliable and developed the Fahrenheit scale. On his original scale, 0° was not the point at which water turns to ice, but rather it was the lowest possible temperature of brine, a mixture of water and salt. And on his original scale, 100° was the average body temperature. That scale has since been adjusted. Now 32° is the temperature at which water freezes, while 212° is the temperature at which it boils, and the average body temperature is 98.6°.

Other scientists were working on measuring temperature in the early 1700s, too. One was a Swedish scientist named Celsius. On his original scale, 0° was the point at which water boiled, and 100° was the point at which it froze. A French scientist named Christin developed a scale with 0° being the freezing point of water and 100° being the boiling point. People began to use these systems, and Christin's "forward" scale became the standard, but the term Celsius was used.

Now the scientific community uses this 0-to-100 system and refers to temperature in "degrees centigrade", but laypeople use the term "degrees Celsius." The Celsius scale, as part of the metric system, is used around the world, but the US is a big exception. They did try to change 40 years ago, when a law called the 1975 Metric Conversion Act was passed, and American school kids began learning the metric system. But older Americans resisted the change, and under Reagan in 1982, the metric system was abandoned. Now, most Americans have no idea if 20°C is warm or cold.

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