# Euler, Leonhard (1707–1783)

Leonhard Euler was a great Swiss mathematician; the second most prolific mathematician in history
(in terms of publications), after Paul Erdös.
His greatest contributions were to number
theory, but Euler also did important work in calculus, geometry, algebra,
probability, acoustics, optics, mechanics, astronomy, artillery, navigation,
and finance. He had a knack of coming up with important results by intuition,
he cast calculus and trigonometry in their modern forms, and he showed the
importance of the number *e*. Even the amusing puzzles
he invented and, in some cases, solved have opened up new mathematical fields.
The bridges of Königsberg problem, for example, heralded the beginning of graph
theory and topology, while his thirty-six
officers problem stimulated important work in combinatorics.
Euler also worked on magic squares and the problem of the knight's tour.

Along with Joseph Lagrange, Pierre Laplace,
and others, Euler helped develop the science of celestial
mechanics. He applied powerful new mathematical techniques to problems
of cometary orbits, planetary perturbations,
and the tides. He also refined the theory of the Moon's motion and calculated
more accurate orbits for Jupiter and Saturn.

Having learned some math from his father, a Calvinist preacher, Euler studied at the University of Basle where he became close friends with members of the Bernoulli family. In 1727, he moved to St. Petersburg, to the court of Catherine the Great, becoming professor of physics (1730) and of mathematics (1733). A devout Christian, Euler met in Russia the encyclopedist and philosopher René Diderot, a notorious atheist. When Diderot heard that Euler had a mathematical proof of the existence of God, he asked for it and was quoted the equation now often to as Euler's formula. Upon losing the use of his right eye, Euler said "Now I will have less distraction." Indeed, the quantity of his output seemed to be inversely proportional to the quality of his sight, because his rate of publication increased after he became almost totally blind in 1766. Euler died moments after calculating the orbit of Uranus on September 18, 1783.