讲座提要：

The calculus of variations was founded by Euler, building upon the work of Leibnz, Jacob and Johann Bernoulli and others, and even earlier,  the invention of the pendulum clock by Huygens and Fermat's principle for the shortest path of light rays. It is also connected with the Principle of Least Action which led to the most famous controversy of the 18th century, involving not only Euler, but also Maupertuis,Voltaire and the Prussian King Frederic the Great. It is a fascinating story with a puzzle, still unsolved today,  about a letter, perhaps by Leibniz, but possibly forged.