Celsius, Centigrade and friends

The 1st century BC physicist and philosopher Philo of Byzantium, was probably the first person to realise that air expands on heating and to use this principle to demonstrate a crude thermometer. There was then little development of this idea for 15 centuries. Then, during the 16th century thermometres began to be developed and the famous Italian physicist and astronomer Galileo Galilei was among the first people to develop a crude thermometer. The first thermometer as we would recognise them was made by Ferdinand II, Grand Duke of Tuscany, in 1641 and was filled with alcohol, rather than mercury which is often used today. Mercury thermometers were then developed within the next 20 years.

Later in the 17th Century thermometer scales began to be developed and various suggestions for what sort of scales would be best. One, suggestion, for example, was based around the temperature of a healthy human and another used the freezing and boiling points of water (on which the Celsius scale we use today is based).

The first scale to gain widespread credibility was developed by the German physicist Fahrenheit in 1714, and his scale is still popular today, particularly in USA and Britain. The Fahrenheit scale is a quite precise and complex scale (it is much more precise than degrees Celsius - there are nearly 2 degrees Celsius in 1 degree Fahrenheit - use this link to convert Fahrenheit to Celsius or vice versa*) and so the search for a simpler scale was on.

Swedish astronomer Anders Celsius developed a much simpler scale in 1742 and an adaptation of this scale is the unit now known as degrees Celsius. Celsius' scale originally used zero as the boiling point of water and 100 as the freezing point of water. This format was not very popular and so the scale was modified and turned upside down. The Frenchman Christen and Swedes Stromer and von Linne were among the first people to do this.

The simplicity of the Celsius scale led to it superseding the Fahrenheit as the universal temperature scale. Centigrade, meanwhile, was a popular name for the Celsius scale for a time and this term literally means 'a 100 grade scale'.

The World Meteorological Organisation decided some time ago that the Celsius scale would be the official temperature scale to be used in the meteorological community and that in honour of Celsius' early work in developing a simple temperature scale the unit of temperature would be known as degrees Celsius as opposed to degrees Centigrade or the Fahrenheit scale!

So, that's how the Celsius scale came to be and that's why temperatures in weather forecasts are (in most places) now quoted in degrees Celsius. Just think though, it could so easily have been degrees Christen, degrees Stromer or degrees von Linne had the World Meteorological Organisation chosen to honour any of these men's efforts!

*to convert Celsius to Fahrenheit simply multiply the Celsius value by 9, divide the answer by 5 and add 32. To convert Fahrenheit to Celsius deduct 32 from the Fahrenheit reading, multiply the answer by 5 and divide this answer by 9.
Mathematically, Celsius = [(Fahrenheit -32) x 5 ] / 9 and Fahrenheit = (Celsius x 9) / 5 + 32.

HOLFORD, I. (1977): The Guiness Book of Weather Facts and Feats, Guiness Superlatives, p240.

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Dan Suri, 16 February 2001