(degree) Celsius (°C)		Anders Celsius (1701–1744)

Anders Celsius was a Swedish astronomer and mathematician who worked in thermometry and studied the Aurora Borealis.

Around 1701 Newton had proposed a temperature scale in which the lower fixed point was 0° and the upper fixed point was 12°. On this scale the boiling point of water was 33°. Celsius was probably aware of this work and built on it in 1742 by proposing a 100 degree scale between the freezing point of water (100° in his original scale) and the boiling point of water (0° in his original scale). He published this proposal in a paper entitled "Observations on two persistent degrees on a thermometer". It is not known what led him to associate the higher value with the colder fixed point, and vice versa. Perhaps he wanted to introduce more originality into his work, or perhaps he was influenced by the Royal Society's temperature scale (used until about 1725), in which the '0' was 'extreme hot' and '90' was extreme cold.

In any case, Celsius' proposed scale was intuitively backwards and was inverted soon after his death so that 0° was the lower fixed point and 100° the upper fixed point. In this way the modern Celsius scale was born. It was accepted as a standard, first in Sweden and France, and then across the globe. Temperature values measured in this scale were originally referred to as degrees "centigrade" ('centi' referring to one hundred, and 'grade' referring to degrees). However, in 1948 Celsius' name became the official temperature unit, when the Ninth General Conference of Weights and Measures declared that 'degrees centigrade' should thereafter be referred to as 'degree Celsius'. In the early 21st Century, only the United States still clings to the Fahrenheit scale; the Celsius scale is the accepted international standard everywhere else.

Celsius was also interested in the Aurora Borealis. In 1724 he and his student Olaf Peter Hiorter noted that the Aurora Borealis are accompanied by deflections of a magnetic compass. This discovery confirmed the relationship between auroras and magnetic fields. Celsius' observations of the aurora were published in Nuremburg, Germany in 1733 in a work entitled Observations of the Northern Lights in Sweden.

For a single temperature-related item listed below (from Ghana), the name Celsius is spelled out. Many other items, indicated only by the symbol °C for degree Celsius, are available on the thermometers, temperatures and temperature units page.

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