Anders Johan Lexell (1740-1784): a Finnish Mathematician and a Russian Academician

Anders Johan Lexell (1740-1784) was born in Turku, Finland. He graduated from the Royal Academy of Åbo (Turku) only 19-years old. His teacher in Mathematics was Martin Johan Wallenius. In Uppsala, he presented a thesis on differential geometry in the plane, which made him known as an excellent geometer in Sweden. However, for lack of positions in Sweden he noticed the activities at the Academy of Sciences in St. Petersburg, where Leonhard Euler had arrived in 1766. His application for work was approved in 1768 and he was invited to St. Petersburg to assist in the calculations for determining the parallax of the sun using the dated collected on the transit of Venus. He started collaborating with Euler on a number of issues, differential and integral calculus, spherical geometry and polygonometry, and orbit calculations. He computed the orbit of the famous "Lexell's comet" and that of Uranus, he proved Lagrange's inversion theorem and discovered Lexell's theorem for spherical triangles. At the peak of his career, in 1780-1781, he visited Berlin, Leipzig, Göttingen, Mannheim, Strasbourg, Paris, London, Oxford, Amsterdam, Hamburg, Copenhagen, Lund, Stockholm and Turku and returned to St. Petersburg. In 1783 he succeeded Euler as professor of "Sublime Mathematics" at the Petersburg Academy of Sciences. He fell ill within a year and died in 1784, only 43-years old.