# Anders Celsius and the Celsius temperature scale

Anders Celsius is one of Uppsala University’s best-known natural scientists. His name is part of the metric system as degrees Celsius or °C, and his temperature scale is used for measuring temperatures in most of the world.

## The celsius temperature scale

Anders Celsius developed his temperature scale after thoroughly investigating the freezing and boiling points of water, finding that they would serve as good reference points when measuring temperatures. He showed that the freezing point is essentially unaffected by air pressure and he determined with remarkable precision how the boiling point of water varies with air pressure. This enabled thermometers to be calibrated under different atmospheric conditions.

The result of his studies was his suggested temperature scale, which had a scale of 100 degrees between the freezing and boiling points of water. More specifically, he used the boiling point of water at mean atmospheric pressure and mean sea level.

He made his first observations with his temperature scale on Christmas Day 1741. However, compared with the modern-day Celsius scale, Anders Celsius’s scale was reversed. He had set the boiling point of water at 0 degrees and the freezing point at 100 degrees. This was perhaps due to the influence of other temperature scales available at the time, or perhaps because he wanted to avoid negative values when recording weather data.

Just over a year later, in 1743, the French scientist Jean-Pierre Christin designed a similar temperature scale: Christin’s scale used the same divisions as Celsius’s scale, but had the freezing point at 0 degrees and the boiling point at 100 degrees. Christin called his scale the centigrade scale.

For a long time, centigrade and degrees Celsius were used interchangeably, but in 1948 the 9th General Conference on Weights and Measures officially designated the temperature scale as the Celsius scale. This was in honour of Anders Celsius’s meticulous work in defining the scale’s end points. It was also done to avoid confusion in the Romance languages where the word centigrade also refers to 1/100th of a right angle.

As part of the metric system, the Celsius temperature scale is now used across the world – even in some countries which generally use imperial units.

## The observatory

Interestingly, Anders Celsius was not primarily a meteorologist but rather an astronomer. In 1730 he was appointed as Professor of Astronomy. This science had been on the decline in Sweden, but according to historian Sten Lindroth, Anders Celsius ‘immediately filled the office with living content and undertook astronomical observations with the poor instruments that were available.’ He undertook the task of creating an observatory in Uppsala as the old one had been destroyed in the Great Fire of 1702. Celsius rebuilt a building on the street Svartbäcksgatan, which today is right in the centre of Uppsala. It was suitably furnished for astronomy, and, as he was very good at raising money, it was also equipped with modern instruments. The observatory was ready in 1741. Celsius, who was a lifelong bachelor, lived in the building himself.

If you have ever walked along Uppsala’s main shopping promenade you may have noticed the yellow Celsius building. It stands out, quite literally, because it is built at an odd angle compared with the surrounding buildings. When the streets were regulated in the 1640s the original building had been allowed to remain as it was.

## The greatest inspiration

Anders Celsius belonged to a well-known scholarly family. His father, Nils Celsius, held the title of professor of mathematics but was best known as headmaster of Katedralskolan in Uppsala. Anders studied at his hometown university and excelled there. However, the main inspiration for his activities was a four-year journey to Germany, Italy and France. He was already a professor at the time.

## The measurment of degrees in Tornedalen

Newton’s theories meant a great deal to Celsius, but even more important was the contact he had with the French mathematician P.L. de Maupertuis, who was a few years older than Celsius. De Maupertuis initiated the measurement of degrees in 1736–1737 that came to occupy such a prominent place in the scientific history of Sweden. According to historian Tore Frängsmyr, the fact that he chose Sweden was primarily thanks to Celsius. The team of six, which included Celsius, set up in Tornedalen.

It was a rough experience. In the summer they were pestered by mosquitoes, and in the winter it was so cold that everything froze, except their alcoholic drinks. But they succeeded and could establish by their measurements that the Earth is flatter at the poles. A French team reached the same conclusions simultaneously in Peru.

## The late years

In recognition of his work, Celsius was awarded an annual state pension of 1,000 livres from France, so financially he was relatively comfortable. But he had led a rough life on his ambitious expeditions and with his nocturnal observations outdoors. He contracted tuberculosis and died at the age of 43. In one respect he was a forerunner of Darwin, as he stubbornly maintained to his dying day that the chronology of the Bible did not square with the findings of scientific research in his field.