Leonhard Euler was a Swiss mathematician and physicist, born on 15th April 1707 in Basel. His father was friends with the renowned mathematician family, the ‘Bernoullis’ and Johann Bernoulli was to have a great impact on Euler’s life later on. When he was only thirteen, Euler entered the University of Basel receiving his Master’s degree in 1723 with a brilliant dissertation to his name, the likes of which could be compared to Issac Newton and René Descartes. On insistence by his father, Euler also studied other subjects such as theology, Greek and Hebrew. Johann Bernoulli who was teaching Euler at the time articulated to his father that he was destined to become a great mathematician and that he should not go for priesthood.

### Work

In 1727, Euler took up a position in the physiology department in Imperial Russian Academy of Sciences in St. Petersburg on the recommendation of Johann Bernoulli. He was later promoted to the mathematics department. While in the Russian capital, Euler mastered the Russian language and decided to settle there permanently also taking up a job as a medic in the Russian Army. In 1731, he was given the post of Professor at the academy. After two years when Daniel Bernoulli left St. Petersburg, Euler was made head of the mathematics department.

When the political situation in Russia got worse, Euler decided to move to Berlin where he took up a post in the Berlin Academy. His stay in Berlin lasted for 25 years during which he wrote numerous articles. Two of his most renowned works are ‘Introductio in analysin infinitorum’ which was published in 1748 and ‘Institutiones calculi differentialis’ published in 1755. The same year he became the member of the Royal Swedish Academy of Sciences.

A compilation of his letters that he wrote tutoring the German princess of Anahalt-Dessau consists of more than two hundred bestselling letters named ‘Letters of Euler on different Subjects in Natural Philosophy Addressed to a German Princess’. His work also included a book on Newtonian dynamics called ‘Mechanica’ which was published in 1737.

### Health Problems

Euler’s health started to deteriorate. In 1735, he suffered from a fatal fever. After that in 1738, he lost eyesight in his right eye and a cataract was found in his left eye in 1766. However his blindness never got in the way of his mathematical career. An excellent memory and exceptional mental ability to calculate made up for his lost eyesight. So much so that he wrote one paper every week in the whole of 1775.

### Later Life and Death

Euler worked in all branches of mathematics including infinitesimal calculus, geometry, algebra and trigonometry. He was the first to present the concept of a function like notation of a trigonometric function along with introducing many notational conventions. He used the letter ‘e’ denoting the base of a natural logarithm called the Euler’s number. ‘Σ’ and ‘π’ were also his inventions. Euler worked with the number theory and the Graph theory. He contributed immensely to the engineering field through his Euler-Bernoulli equation. He is recognized for use of diagrams of ‘closed curves’ to demonstrate ‘syllogistic’ reasoning. These are known as Euler Diagrams.

Euler spent the last days of his life in Russia. He died of a brain hemorrhage on 18th September 1783.