Leonhard Euler. Engraving of Leonard Euler (1707- 1783), Swiss mathematician. He developed the theory of differential equations, the calculus of variations, and did important work in astronomy and optics. A pupil of Johann Bernoulli, he became professor of physics at the University of St Petersburg, Russian, in 1730. In 1741 he was invited to Berlin by Frederick the Great, where he spent 25 years before returning to Russia. He was totally blind in the last years of his life, but an ability to calculate in his head ensured that his productivity did not diminish. He published 800 papers, contributing to all areas of mathematics. Engraving published between 1833-1837