Anders Celsius

Anders Celsius was born in Uppsala, Sweden, in 1701, into a family of scientists — both his grandfathers were professors, and his father taught astronomy. He became professor of astronomy at Uppsala University in 1730 and founded the Uppsala Astronomical Observatory in 1741, the oldest in Sweden.

Celsius was an accomplished observational astronomer. He travelled across Europe visiting major observatories, and in 1736 took part in the French Academy's expedition to Lapland led by Maupertuis to measure the length of a degree of meridian near the pole. The expedition's results confirmed Newton's prediction that the Earth is flattened at the poles, a major vindication of Newtonian physics, and made Celsius well known in European science.

In 1742 Celsius proposed a temperature scale with exactly 100 degrees between the freezing and boiling points of water — but in the reverse of the modern convention, setting 0 for the boiling point and 100 for the freezing point. The scale was inverted to its present form within a few years of his death; the botanist Carl Linnaeus is among those credited with the reversal. Celsius valued the scale for its decimal simplicity and its reliance on two universally reproducible fixed points.

Celsius also made early studies of the aurora borealis and was among the first to connect it with the Earth's magnetic field. He died of tuberculosis in 1744, at just 42; the centigrade scale was officially renamed in his honour in 1948.