### Happy birthday, Leonhard Euler!

Leonhard Euler, born on the 15th of April 1707 in Basel, Switzerland, would have turned 300 yesterday! In the current issue *Plus* kicks of a celebratory series of articles with Robin Wilson's "Read Euler, read Euler, he is the master of us all.". Here is a taster of Wilson's article.

Euler was the most prolific mathematician of all time. He wrote more than 500 books and papers during his lifetime — about 800 pages per year — with an incredible 400 further publications appearing posthumously. His collected works and correspondence are still not completely published: they already fill over seventy large volumes, comprising tens of thousands of pages.

Euler worked in an astonishing variety of areas, ranging from the very pure — the theory of numbers, the geometry of a circle and musical harmony — via such areas as infinite series, logarithms, the calculus and mechanics, to the practical — optics, astronomy, the motion of the Moon, the sailing of ships, and much else besides. Indeed, Euler originated so many ideas that his successors have been kept busy trying to follow them up ever since. Not surprisingly, many concepts are named after him: Euler's constant, Euler's polyhedron formula, the Euler line of a triangle, Euler's equations of motion, Eulerian graphs, Euler's pentagonal formula for partitions, and many others.

Euler's career took him from his native Basel to the Academy at St Petersburg, where he eventually became Professor of Mathematics, to the Berlin Academy, on invitation from Prussia's Frederick the Great, and finally back to St Petersburg. He fathered thirteen children, of whom only five survived to adolescence, and reportedly carried out mathematical researches with a baby on his lap.

He died in St Petersburg on the 18th of September 1783. In a eulogy by the Marquis de Condorcet, we read about his final afternoon:

*On the 7th of September 1783, after amusing himself with calculating on a slate the laws of the ascending motion of air balloons, the recent discovery of which was then making a noise all over Europe, he dined with Mr Lexell and his family, talked of Herschel's planet (Uranus), and of the calculations which determine its orbit. A little after, he called his grandchild, and fell a playing
with him as he drank tea, when suddenly the pipe, which he held in his hand, dropped from it, and he ceased to calculate and to breathe.*

The *Plus* article "Read Euler, read Euler, he is the master of us all." gives a broad overview of Euler's life and work, but you can also find out more in the following articles:

*posted by Plus @ 9:05 AM*

## Comments

## Euler's Constant

Euler's constant originates from a formula in the Supplement to De Moivre's Miscellanea Analytica (1730) containing the Bernoulli numbers. Due to the Bernoulli numbers this formula is unfortunately divergent, but Euler amends this formula to make it nearly convergent.