Celsius – A pioneer in investigating the Earth and its changes

°C, as we know, stands for degrees Celsius, but who was Celsius? Celsius was a pioneer in investigating the Earth and its changes by means of systematic observations and by collecting long series of numerical data, among other things temperature. He started this work in Uppsala in 1722.

Anders Celsius lived in 1701 – 1744; he grew up in a family of astronomers in Uppsala, but in rather poor circumstances. At the age of 28 he was appointed professor of astronomy, but his main interest was our own planet.

Celsius first made a study tour to Germany, Italy, France and England during four years, then he participated in a French scientific expedition to the Arctic Circle during one year, and after that he founded an observatory in Uppsala (close to his mother’s restaurant). However, his life became short; he died, unmarried but with many friends, in a lung disease only 42 years old. But what did he actually do?

Arctic Circle expedition and Newton’s theories

Newton’s theories of gravitation and centrifugal force at this time were disputed. In Paris intense discussions for and against took place, and one had in mind trying to solve the question by determining if the Earth due to the rotation was somewhat flattened at the poles. At this moment Celsius arrived there, and he suggested that the contemplated expedition should go to the Arctic Circle in Sweden, to the Torne valley.

Celsius now became a member of the French expedition which performed measurements at the Arctic Circle in 1736 – 1737, both towards stars in the winter cold and between mountain peaks during summer. Also gravity was measured there. The results were then compared with corresponding ones around Paris.

The expedition itself did not manage to solve the controversial problem, but together with earlier observations of other phenomena it made the balance in the discussion finally tip over in favour of Newton.

Observatory, zero meridian, and gravity

Inspired by what he had seen in Paris and Greenwich, Celsius, after returning from the Arctic Circle, succeeded in persuading the University to found an observatory in Uppsala in 1739. The building is still there, standing ”askew” in central Uppsala. Here Celsius worked for the rest of his short life, together with his diligent assistants Olof Hiorter and Pehr Wargentin.

Celsius engaged in new methods using celestial bodies to determine latitude and longitude on the Earth’s surface, important for mapping, and he made the Uppsala Observatory the first zero meridian in Sweden. Together with Wargentin he made Uppsala internationally leading within longitude determination.

Celsius also could determine gravity in Uppsala, with a pendulum clock mounted in the Observatory and constructed by a specialist in London. This was one of only few gravity stations in the world at this time.

Sea level and land uplift

Celsius had early taken an interest in the phenomenon then called the water decrease, today known as the land uplift after the Ice Age, or the postglacial rebound; he succeeded in 1743 to determine, for the first time, its rate. For this he used an old seal rock, a rock where long ago seals could be shot when they rested close to the then mean sea level. The result was slightly more than 1 cm/yr, about the correct value.

Based on this value, Celsius then the draw the conclusion that large regions in Sweden must have been below sea level a few thousand years ago. He made natural science enter into history.

Celsius had, for the benefit of future generations, a special mark for the mean sea level 1731 cut into another seal rock. It turned out to be valuable one century later when it could be used to show that the phenomenon was a land uplift and not a water decrease.

Temperature scale and temperature series

Celsius had since 1722 not only measured temperature but compared different thermometers and temperature scales. He found none of them reliable and therefore constructed, after much testing, his own temperature scale in 1742, defined by the freezing and boiling points of water at normal air pressure. The interval in between he divided into 100 degrees. Today this is the international unit for temperature.

Also regarding temperature Celsius had in mind the benefit for future generations; he expected a weather journal to be continued in Uppsala for all time. Today the temperature series of Uppsala commencing in 1722 is one of the longest in the world.

Already in the latter part of the 1700s Wargentin could make use of the temperature series to study climate changes, nowadays a highly urgent subject.

Magnetic field and northern lights

When Celsius was in London he had, by the instrument specialist there, ordered a kind of large compass with a needle being especially long. With this he studied, in Uppsala, variations in the direction of the magnetic field, pondering over whether they could be connected with phenomena in the atmosphere.

In winter 1741 Celsius and his assistant Hiorter noted that the magnetic needle behaved strangely at the same time as the northern lights appeared in the sky. Moreover, Celsius showed, through a cooperation with London, that a similar magnetic needle there behaved strangely at the same time as the one in Uppsala. Hiorter and Celsius had discovered that there had to be a connection between the northern lights and the magnetic field.

Today this connection is fundamental for the understanding of the phenomenon of the northern lights and the role played by the sun in the whole thing.

Text by Martin Ekman, reader of geophysics and author of the book “The Man behind ‘Degrees Celsius’: A Pioneer in Investigating the Earth and its Changes”.