Temperature > 13 - Anders Celsius

He was a Swedish astronomer known worldwide for his thermometric scale.

He was born in Uppsala, Sweden, on November 27, 1701.

He became a professor of astronomy in 1730.

From 1732 he visited and worked in most of the European astronomical observatories for 4 years.

In 1736 he participated in the “Lapland Expedition” of the French astronomer Maupertius to Torneå (northern Sweden) to measure the length of a degree along a meridian near the pole and compare it with that measured in Peru, near the Equator. Newton's prediction that the Earth has an ellipsoidal shape, flattened at the poles, was confirmed. Celsius used the prestige gained from his participation in this expedition to build the modern “Celsius Observatory” in Uppsala, which was completed in 1741. That year he published the book “Arithmetic for Swedish Youth”.

The Celsius scale originated in his article “Observations on Two Persistent Degrees in a Thermometer” from 1742. Celsius observed over two years that the thawing of snow or ice, in places at different latitudes and with different atmospheric pressures, always occurred at the same point on the thermometer. He used this “fixed point” as a reference for 100 degrees. The other “fixed point” chosen was the one corresponding to the boiling of water at a pressure of 755 mm of mercury, to which he associated 0 degrees. He divided the distance between the two points into 100 equal parts, thus obtaining the so-called Celsius scale for measuring temperatures. Choosing 0 degrees for the boiling temperature of water avoided the use of negative temperatures. After his death, the “fixed points” 0 and 100 were swapped, leaving the scale as we know it today. It is believed that the person responsible for the change was the scientific instrument maker Daniel Ekström, although Strömer and, less certainly, Carl von Linné are also mentioned. Given the nature of the scale, its unit was called “degree centigrade” for many years. In 1948, the CIPM (Comité International des Poids et Mesures) decided to replace that name with “degree Celsius”.

The observation of the deflection of a magnetic needle led Celsius and his assistant Olof Hiorter to conclude that the phenomenon of the aurora borealis has magnetic causes.

Celsius carried out numerous astronomical works, using a photometric system of his own to determine the magnitude of stars. He published most of his works at the Royal Society of Sciences in Uppsala and the Royal Swedish Academy of Sciences.

He died of tuberculosis in April 1744, aged 42.