Anders Celsius
1701-1744
Swedish Astronomer and Mathematician
Anders Celsius opened Sweden to modern European science and initiated reforms in his country's astronomy curriculum. Known as the founder of Swedish astronomy, he is today remembered for establishing the centigrade scale, which bears his name.
Celsius was born in Uppsala on November 27, 1701. He studied astronomy and mathematics, and in 1725 became secretary of Uppsala's Scientific Society. After teaching mathematics for a few years he succeeded his father as professor of astronomy at Uppsala University (1730).
An ecclesiastical ban on teaching of Copernican theory and lack of astronomical instruments in Sweden obliged Celsius to travel abroad to complete his studies and practical training. His first stop was the new observatory in Berlin where he assisted Christfried Kirch (1694-1740) in taking observations (1732-33). He then traveled to Nuremberg where he initiated an international astronomical review and published his aurora boerealis observations. He then visited Venice, Padua, and Bologne before proceeding to Rome and then Paris.
His arrival in Paris coincided with an ongoing debate over Earth's shape. Isaac Newton (1642-1727) had argued Earth's axial rotation would cause bulging at the equator and flattening at the poles where as René Descartes' (1596-1650) vortex theory implied Earth would be flattened about the equator and elongated along the polar axis. Most Academy of Science members supported Descartes' theory; but, Pierre Louis Maupertuis (1698-1759) spoke out in support of Newton (1732). More accurate measurements were required to settle the matter. In 1733 Charles-Marie La Condamine (1701-1774) proposed an expedition to measure Earth's curvature where it was expected to be greatest—the equator. His expedition departed in May 1735.
Maupertuis proposed a similar expedition to measure Earth's curvature in the Arctic. Celsius, having already made Maupertuis' acquaintance, was consulted about a suitable location. Torneå in Swedish-Finnish Lapland was selected, and Celsius was invited to join the expedition.
Preliminary preparations made, Celsius left for London in July 1735 with the dual purpose of continuing with his studies and purchasing instruments for the expedition. He departed England in April 1736 and soon after sailed from Dunkerque with Maupertuis' expedition. Their work was completed in less than a year, with their measurements supporting Newton's theory. But their work was challenged, and Celsius participated in the ensuing debate. The matter was only decisively settled in Newton's favor with the return of La Condamine's expedition (1744).
Upon resuming his academic post at Uppsala in 1737, Celsius undertook the establishment of Sweden's first modern observatory, which opened in December 1742. While engaged in this project, Celsius also attempted to determine the magnitude of stars in the constellation Aries by purely photometric means (1740) and worked at reforming academic instruction of astronomy.
From early on Celsius began taking daily meteorological measurements. His efforts were however hampered by inaccurate thermometers, and he sought to make a more reliable instrument by employing a fixed scale based on two invariable, naturally occurring points. His lower fixed point was determined by immersing the instrument in melting ice, the upper point by placing it in boiling water. He set the upper point at 0° and the lower at 100° thus producing the first centigrade thermometer. His instrument was ready for use on December 25, 1741.
Confusion still exists over priority for the centigrade thermometer. Carolus Linnaeus (1707-1778) inverted the scale shortly after Celsius' death in 1744 and is sometimes given credit. But a centigrade thermometer with the freezing point at 0° had been built sometime before 1743 by Jean Pierre Christian (1683-1755). If one considers the scale with a freezing point of 100° as the one used today then Celsius was first. If not, the strongest priority claim is Christian's.
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