Editing Leonhard Euler (section)

=== Berlin ===
Concerned about the continuing turmoil in Russia, Euler left St. Petersburg in June 1741 to take up a post at the [[Prussian Academy of Sciences|Berlin Academy]], which he had been offered by [[Frederick the Great of Prussia]].{{sfn|Gautschi|2008|p=7}} He lived for 25 years in [[Berlin]], where he wrote several hundred articles.<ref name="zum werk leonhard" /> 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.<ref name="dartm" />{{sfn|Dunham|1999|pp=xxiv–xxv}} In 1755, he was elected a foreign member of the [[Royal Swedish Academy of Sciences]]<ref name=sten/> and of the [[French Academy of Sciences]].<ref name="volumes"/> Notable students of Euler in Berlin included [[Stepan Rumovsky]], later considered as the first Russian astronomer.<ref name="BEA"/><ref name="ClarkGolinski1999"/> In 1748 he declined an offer from the University of Basel to succeed the recently deceased Johann Bernoulli.<ref name="zum werk leonhard" /> In 1753 he bought a house in [[Charlottenburg]], in which he lived with his family and widowed mother.<ref name="zum 300 knobloch"/>{{sfn|Gautschi|2008|pp=8–9}}

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 to a German Princess|Letters of Euler on different Subjects in Natural Philosophy Addressed to a German Princess]]''.<ref name='Digital Copy of "Letters 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.{{sfn|Dunham|1999|pp=xxiv–xxv}}

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 of Prussia|Frederick II]] named himself as its president.{{sfn|Gautschi|2008|pp=8–9}} 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.{{sfn|Dunham|1999|pp=xxiv–xxv}} Frederick also expressed disappointment with Euler's practical engineering abilities, stating:

{{blockquote|I wanted to have a water jet in my garden: Euler calculated the force of the wheels necessary to raise the water to a reservoir, from where it should fall back through channels, finally spurting out in [[Sanssouci]]. My mill was carried out geometrically and could not raise a mouthful of water closer than fifty paces to the reservoir. Vanity of vanities! Vanity of geometry!<ref name=fredlett/>}}

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.<ref name=Lynch/>

Throughout his stay in Berlin, Euler maintained a strong connection to the academy in St. Petersburg and also published 109 papers in Russia.<ref name="vucinich"/> He also assisted students from the St. Petersburg academy and at times accommodated Russian students in his house in Berlin.<ref name="vucinich" /> In 1760, with the [[Seven Years' War]] raging, Euler's farm in Charlottenburg was sacked by advancing Russian troops.<ref name="zum 300 knobloch" /> Upon learning of this event, [[Ivan Saltykov|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.<ref name="gindikin" /> Euler decided to leave Berlin in 1766 and return to Russia.{{sfn|Gautschi|2008|p=9}}

During his Berlin years (1741–1766), Euler was at the peak of his productivity. He wrote 380 works, 275 of which were published.<ref name="math at prussian"/> This included 125 memoirs in the Berlin Academy and over 100 memoirs sent to the [[Russian Academy of Sciences|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.<ref name="historian's craft"/> He was even involved in the design of the water fountains at [[Sanssouci]], the King's summer palace.<ref name="fountains"/>