An old idiom, employed by many writers over the years, claims that nothing is certain except death and taxes. One example appears in Daniel Defoe's 1726 book, *The Political History of the Devil*, which runs thus:

Things as certain as death and taxes, can be more firmly believ’d. [Def, p. 269]

The year 1783 brought two particular events to the world, one undeniably certain and one profoundly uncertain.

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On September 19, 1783, a sheep, a duck, and a rooster, became the first non-human animal passengers aboard a hot air balloon constructed by the brothers Montgolfier, Joseph-Michel and Jacques-Etienne, who spent the past few months experimenting with their flying device. The balloon, dubbed the Aérostat Réveillon (mention Réveillon here), lifted off the grounds of royal palace at Versailles and flew for about x minutes and up to y meters under a crowd that included the King Louis XVI and his Queen Marie Antoinette. (Need source).

In St. Petersburg Russia the night before, Leonhard Euler succumbed from a brain hemorrhage earlier that day. His death has been romanticized to the point.... It is true, however, that Euler continued to work until his dying day. Euler had left calculations on his slate describing the ascent of an aerostatic globe, roused by the public demonstration of the flight of a passenger-less hot air balloon that the Montgolfier brothers performed in Annonay, France in early June.

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The first was the death, on September 18 of that year, of the famed Swiss mathematician Leonhard Euler, at his home in St. Petersburg, Russia. The second was the report in June of lighter-than-air flight by the brothers Joseph-Michel and Jacques-Étienne Montgolfier, at the town of Annonay, France.

The death of such a luminary as Euler was, if not unexpected, a profound loss for the mathematical community. Over his 56 year career, Euler contributed to such disparate fields as astronomy, number theory, mechanics, calculus, graph theory, and music theory. His prowess at mental calculation was widely known, [[anecdote here]] In the Marquis de Condorcet's eulogy, Euler's death occurred suddenly in the bucolic setting of his St. Petersburg estate:

...he had his grandson come and play with him and took a few cups of tea, when all of a sudden the pipe that he was smoking slipped from his hand and he ceased to calculate and live. [Con]

Euler's influence would continue long after his death, with many of his works not published until 1862. All told, he wrote over 800 papers in mathematics and science, and some 30 books. His work revolutionized the mathematical sciences. However, Euler's work in the mathematical sciences had a more specific impact immediately after his death. Immediately before reporting the death of Euler in his eulogy, Condorcet wrote on Euler's particular interest in the weeks leading up to his death:

On 7 September 1783, after having enjoyed some calculations on his blackboard concerning the laws of ascending motion for aerostatic machines for which the recent discovery was the rage of Europe, he dined with Mr. Lexell and his family, spoke of Herschel’s planet and the mathematics concerning its orbit... [Con]

As we see here, Euler was engaged in the study of the Mongolfier brothers' novel "aerostatic machines" on the very day of his death. The calculations of their motion remained on the blackboard even as Euler himself "ceased to calculate and live." The following year, a short piece appeared in the *Memoires *of the Paris Academy, titled "Calculs sur les Ballons aérostatiques faits par feu M. Léonard Euler, tels qu'on les a trouvés sur son ardoise, après sa mort arrivée le 7 Septembre 1783" ("Calculations on aerostatic Balloons made by the late Mr. Leonhard Euler, as they were found on his blackboard, after his death on September 7, 1783."). Euler's son, Johann-Albrecht, had forwarded a copy of these calculations to the Paris Academy, thus preserving the work in the public record.

##### References

[Def] Defoe, Daniel. *The Political History of the Devil*, *As Well Ancient And Modern: In Two Parts.* London: Black Boy, 1726.

[Con] Condorcet, Marquis de. *Eulogy of Euler. *[http://eulerarchive.maa.org/historica/condorcet.html]