First Saint Petersburg period (1727–1741) stamp commemorating the 250th birthday of Euler. The text says: 250 years from the birth of the great mathematician, academician Leonhard Euler. Johann Bernoulli's two sons,
Daniel and
Nicolaus, entered into service at the
Imperial Russian Academy of Sciences in
Saint Petersburg in 1725, leaving Euler with the assurance they would recommend him to a post when one was available. On 31 July 1726, Nicolaus died of appendicitis after spending less than a year in Russia. When Daniel assumed his brother's position in the mathematics/physics division, he recommended that the post in physiology that he had vacated be filled by his friend Euler. In November 1726, Euler eagerly accepted the offer, but delayed making the trip to Saint Petersburg while he unsuccessfully applied for a physics professorship at the University of Basel. Euler arrived in Saint Petersburg in May 1727. He was promoted from his junior post in the medical department of the academy to a position in the mathematics department. He lodged with Daniel Bernoulli with whom he worked in close collaboration. Euler mastered Russian, settled into life in Saint Petersburg and took on an additional job as a medic in the
Russian Navy. The academy at Saint Petersburg, established by
Peter the Great, was intended to improve education in Russia and to close the scientific gap with Western Europe. As a result, it was made especially attractive to foreign scholars like Euler. The academy's benefactress,
Catherine I, who had continued the progressive policies of her late husband, died before Euler's arrival to Saint Petersburg. The Russian conservative nobility then gained power upon the ascension of the twelve-year-old
Peter II. The nobility, suspicious of the academy's foreign scientists, cut funding for Euler and his colleagues and prevented the entrance of foreign and non-aristocratic students into the Gymnasium and universities. Conditions improved slightly after the death of Peter II in 1730 and the German-influenced
Anna of Russia assumed power. Euler swiftly rose through the ranks in the academy and was made a professor of physics in 1731. In 1730, he began a lengthy correspondence with the secretary of the academy
Johann Daniel Schumacher which continued until 1757, long after Euler had left for Berlin, comprising over three hundred letters in total. They shared scientific news and Euler advised Schumacher on suitable candidates for vacancies at the academy (such as the mathematician and astronomer
Tobias Mayer, the natural philosopher , and the mathematician and philosopher ), as well as sending scientific equipment and his own latest publications. From the 1750s, he corresponded similarly with
Gerhard Friedrich Müller, to whom Schumacher delegated many of his responsibilities. In 1731 Euler also left the Russian Navy, refusing a promotion to
lieutenant. Two years later, Daniel Bernoulli, fed up with the censorship and hostility he faced at Saint Petersburg, left for Basel. Euler succeeded him as the head of the mathematics department. In January 1734, he married Katharina Gsell (1707–1773), a daughter of
Georg Gsell.
Frederick II had made an attempt to recruit the services of Euler for his newly established
Berlin Academy in 1740, but Euler initially preferred to stay in St Petersburg. But after Empress Anna died and Frederick II agreed to pay 1600
ecus (the same as Euler earned in Russia) he agreed to move to Berlin. In 1741, he requested permission to leave for Berlin, arguing he was in need of a milder climate for his eyesight. The Russian academy gave its consent and would pay him 200 rubles per year as one of its active members.
Berlin period (1741–1766) Concerned about the continuing turmoil in Russia, Euler left St. Petersburg in June 1741 to take up a post at the
Berlin Academy, which he had been offered by
Frederick the Great of Prussia. He lived for 25 years in
Berlin, where he wrote several hundred articles. In 1748 his text on functions called the
Introductio in analysin infinitorum was published and in 1755 a text on
differential calculus called the
Institutiones calculi differentialis was published. In 1755, he was elected a foreign member of the
Royal Swedish Academy of Sciences and of the
French Academy of Sciences. Notable students of Euler in Berlin included
Stepan Rumovsky, later considered as the first Russian astronomer. In 1748 he declined an offer from the University of Basel to succeed the recently deceased Johann Bernoulli. In 1753 he bought a house in
Charlottenburg, in which he lived with his family and widowed mother. Euler became the tutor for
Friederike Charlotte of Brandenburg-Schwedt, the Princess of
Anhalt-Dessau and Frederick's niece. He wrote over 200 letters to her in the early 1760s, which were later compiled into a volume entitled
Letters of Euler on different Subjects in Natural Philosophy Addressed to a German Princess. This work contained Euler's exposition on various subjects pertaining to physics and mathematics and offered valuable insights into Euler's personality and religious beliefs. It was translated into multiple languages, published across Europe and in the United States, and became more widely read than any of his mathematical works. The popularity of the
Letters testifies to Euler's ability to communicate scientific matters effectively to a lay audience, a rare ability for a dedicated research scientist. Despite Euler's immense contribution to the academy's prestige and having been put forward as a candidate for its presidency by
Jean le Rond d'Alembert,
Frederick II named himself as its president. The Prussian king had a large circle of intellectuals in his court, and he found the mathematician unsophisticated and ill-informed on matters beyond numbers and figures. Euler was a simple, devoutly religious man who never questioned the existing social order or conventional beliefs. He was, in many ways, the polar opposite of
Voltaire, who enjoyed a high place of prestige at Frederick's court. Euler was not a skilled debater and often made it a point to argue subjects that he knew little about, making him the frequent target of Voltaire's wit. Frederick also expressed disappointment with Euler's practical engineering abilities, stating: However, the disappointment was almost surely unwarranted from a technical perspective. Euler's calculations look likely to be correct, even if Euler's interactions with Frederick and those constructing his fountain may have been dysfunctional. Throughout his stay in Berlin, Euler maintained a strong connection to the academy in St. Petersburg and also published 109 papers in Russia. He also assisted students from the St. Petersburg academy and at times accommodated Russian students in his house in Berlin. In 1760, with the
Seven Years' War raging, Euler's farm in Charlottenburg was sacked by advancing Russian troops. Upon learning of this event,
General Ivan Petrovich Saltykov paid compensation for the damage caused to Euler's estate, with
Empress Elizabeth of Russia later adding a further payment of 4000 rubles—an exorbitant amount at the time. Euler decided to leave Berlin in 1766 and return to Russia. During his Berlin years (1741–1766), Euler was at the peak of his productivity. He wrote 380 works, 275 of which were published. This included 125 memoirs in the Berlin Academy and over 100 memoirs sent to the
St. Petersburg Academy, which had retained him as a member and paid him an annual stipend. Euler's
Introductio in Analysin Infinitorum was published in two parts in 1748. In addition to his own research, Euler supervised the library, the observatory, the botanical garden, and the publication of calendars and maps from which the academy derived income. He was even involved in the design of the water fountains at
Sanssouci, the King's summer palace.
Second Saint Petersburg period (1766–1783) The political situation in Russia stabilized after
Catherine the Great's accession to the throne, so in 1766 Euler accepted an invitation to return to the St. Petersburg Academy. His conditions were quite exorbitant—a 3000 ruble annual salary, a pension for his wife, and the promise of high-ranking appointments for his sons. At the university he was assisted by his student
Anders Johan Lexell. While living in St. Petersburg, a fire in 1771 destroyed his home. ==Personal life==