Jérôme Lalande

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Joseph Jérôme Le Français de Lalande

Joseph Jérôme Lefrançais de Lalande (born July 11, 1732 in Bourg-en-Bresse , France , † April 4, 1807 in Paris ) was a French mathematician and astronomer during the Enlightenment and the French Revolution . During the revolution, he dropped the nobility predicate "de".

Live and act

Lalande attended a Jesuit school and then began studying law . After he met the astronomer Joseph Nicolas Delisle in Paris , he studied astronomy and theoretical physics with Pierre Lemonnier .

Despite being a dedicated observer as Delisle's assistant , he completed his law degree in 1751 and practiced in his home town of Bourg-en-Bresse . After stimulating contacts with Pierre-Louis Moreau de Maupertuis and Leonhard Euler in Berlin, Lalande published some reductions in his measurements in the communications of the academies in Berlin and Paris. His work led to his appointment as a foreign member of the Prussian Academy of Sciences and, in 1752, director of the Berlin observatory . In 1753 he was elected to the Académie des Sciences . Then there was a dispute with his teacher Lemonnier about the correct calculation of the flattening of the earth, which was needed for calculating the lunar orbit ( equatorial horizontal parallax ). A commission from the Paris Academy decided in favor of Lalandes. For him, however, it was only a " Pyrrhic victory " because his relationship with his teacher Lemonnier then cooled down. In 1764 Lalande was elected a foreign member of the Göttingen Academy of Sciences .

Calculation of the orbit of Halley's comet

Lalande then worked as assistant to Alexis-Claude Clairaut on a better orbit calculation of Halley's comet , where he dealt with the three-body problem like Clairaut, d'Alembert and Euler . Using Clairaut's methods, Lalande was able to successfully calculate the comet's orbital disturbances caused by large planets . He was supported in the extensive arithmetic work by Nicole-Reine Lépaute (1723–1788), whose contribution, like that of other female mathematicians at the time, who were allowed to do “arithmetic” for their male colleagues, was largely ignored. Lalande recognized her work as follows:

For six months we did the math from morning to night. Mme. Lépautes' help was such that without her I would not have been able to start the enormous work at all. It was necessary to calculate the distance of the two planets Jupiter and Saturn to the comet separately for each successive degree over 150 years.

Later on, Lalande often cooperated with female mathematicians. Lalande's partner Louise du Pierry (born 1746) later became the first female astronomy professor.

For “Halley”, because of the unusually strong orbit disturbances caused by Jupiter , he calculated that the comet would come a few months later than assumed when it approached the earth's orbit next . Charles Messier had looked in vain for the comet expected in 1757; it was first sighted by Johann Georg Palitzsch at the end of 1758 and the perihelion in March 1759 was accurate to within four weeks - which was a great success for the new perturbative methods. Lalande's prediction was viewed by contemporaries as a triumph of the mainly mechanistic worldview of the Enlightenment .

Today we know through other methods (mainly thanks to the numerical integration of small steps made possible by computers ) that Halley's orbital period changed by one year not only then: its value, which averages 76 years, fluctuated between the last 2000 years 74 and 79 years.

It was only 40 years after Lalande that Wilhelm Olbers succeeded in developing faster methods of calculating the orbit of comets.

University professor

After this success, Lalande succeeded his teacher Deslisle as professor of astronomy at the Collège Royale in 1762, which he remained until his death. From 1760 to 1776 he was also editor of the Connaissance des temps , the most important astronomical yearbook in France. In 1791 he became rector of the College de France and, among other things, pushed through the admission of female students.

As an astronomer, for example, he worked on the development of "lunar distances" to stars, which at the time was regarded as a method of solving the longitude problem , which was very important for shipping navigation .

Lalande was also involved in the processing of the data for the passages of Venus in 1761 and 1769, carried out by James Cook in the South Seas ( Endeavor expedition, Charles Green carried out the observations in Tahiti in June 1769 ). In 1771 Lalande succeeded in submitting an improved calculation of the Earth's orbit based on worldwide observations of the Venus transit of 1761 and 1769. His specification of this " astronomical unit " of 153 ± 1 million km already agrees with the current value of 149.6 million km to within 2%. Johann Franz Encke received the same value in 1835, while Pingrè came to 142.9 million km.

On November 24, 1763 Lalande was inducted into the Royal Society . In 1764 his textbook on astronomy appeared, which was also a manual for measurements and their "reduction" and measuring instruments. The calculation methods for comet orbits described therein influenced the young businessman Friedrich Wilhelm Bessel to turn to astronomy in 1800. Lalande also wrote popular science books such as his "Astronomy des Dames".

From 1765 to 1766 he traveled to Italy , where at an audience he asked the Pope to remove the works of Nicolaus Copernicus and Galilei from the "Index". In 1769 his extensive travelogue from Italy appeared. On another trip to England, he also saw Harrison's famous clocks in Greenwich , which in an improved form finally solved the problem of length.

In 1781 Lalande was elected to the American Society of Arts and Sciences . From 1783, his most gifted student, Jean-Baptiste Joseph Delambre, was his assistant, whom Lalande described in 1788 (letter to Bugge) as “the world's most capable astronomer at the time”. After Delambre had received the Academy Grand Prix for his calculation of the Uranus orbit in 1789 , Lalande gave him the name of his observatory.

In May 1795 Lalande became director of the Paris observatory . A first star catalog was created with 30,000 stars, expanded to 41,000 in 1797. His niece in law and illegitimate daughter Marie-Jeanne de Lalande (Amélie Harlay, 1768-1832) and his cousin Michel, husband of Marie-Jeanne, were his employees.

The enlightener Lalande was known to be an atheist , which was an advantage during the French Revolution. In 1799 his dictionary for atheists appeared , in which he later included Napoleon Bonaparte , to his displeasure . Its "ugliness" was the target of many contemporary caricatures . He himself took no offense and was not disturbed by it in his relationships with women.

His joke is expressed in the following anecdote, for example. It was common knowledge that Voltaire , with whom Lalande was on friendly terms, did not like cats. When Voltaire blasphemed that they had not even made it under the 33 constellations as animals, the avowed cat lover Lalande named a constellation Felis (cat). However, it was not well received by many astronomers and was therefore only found on some sky maps. However, the decision first European astronomers Congress 1798 in Gotha , where he invited by Franz Xaver von Zach with Johann Elert Bode met that of Lalande also proposed " hot air balloon " should remain. This constellation was also banned from official maps by 1922 at the latest.

Freemason and encyclopedist

Jérôme Lalande is listed among the 72 names of great people on the Eiffel Tower .

With his friend Claude Adrien Helvétius , the Enlightenment founded one of the most important Masonic lodges of the Age of Enlightenment , the so-called Neuf Sœurs Philosophers Lodge in Paris. He himself was their first lodge master . For the Encyclopedia by Diderot and d'Alembert he contributed 250 articles in the field of astronomy.

Jérôme Lalande died at the age of 74 and was buried at the Cimetière du Père Lachaise in Paris.

Eponyms

The asteroid (9136) Lalande , discovered on May 13, 1971, was named after him on April 2, 1999. The lunar crater Lalande is also named after him.

Fonts

Voyage d'un françois en Italie, fait dans les années 1765 et 1766. Tome premier , 1769
  • Traité d'astronomie , 1764, another 4 volumes 1771–1781, and in 1792 the 3rd edition appeared, edited by Delambre
  • Abrégé de navigation historique, théorétique, et practique , (navigation tables) 1793
  • Voyage d'un françois en Italie , 1769 (8 volumes, travelogue)
  • Astronomical manual or the star art in a short teaching term. Flittner & Müller, Leipzig 1775 ( digitized version )
  • Astronomy des dames 1785, new editions 1795, 1806
  • Histoire céleste française , 1801 (with an appendix with 47,000 cataloged stars).
  • Logarithmic trigonometric tables. Increased by the tables of the Gaussian logarithms. Tauchnitz, Leipzig 1844 ( digitized version )

Web links

Notes and individual references

  1. ↑ Lalande, Joseph-Jérôme LE FRANÇAIS de . In: Werner Hartkopf: The Berlin Academy of Sciences. Its members and award winners 1700–1990. Akademie Verlag, Berlin 1992, ISBN 3-05-002153-5 , p. 204.
  2. ↑ Holger Krahnke: The members of the Academy of Sciences in Göttingen 1751-2001 (= Treatises of the Academy of Sciences in Göttingen, Philological-Historical Class. Volume 3, Vol. 246 = Treatises of the Academy of Sciences in Göttingen, Mathematical-Physical Class. Episode 3, vol. 50). Vandenhoeck & Ruprecht, Göttingen 2001, ISBN 3-525-82516-1 , p. 143.
  3. ↑ There are different spellings such as Elisabeth Louise Felicite Pourri de la Madeleine du Piéry
  4. ↑ Napoleon tried to approach the church again. Lalande was criticized for being accepted by the academy.
  5. ↑ knerger.de: The grave of Jérôme Lalande
  6. ↑ Minor Planet Circ. 34350
personal data
SURNAME Lalande, Jérôme
ALTERNATIVE NAMES Lalande, Joseph Jérôme Lefrançais de (full name)
BRIEF DESCRIPTION French mathematician and astronomer
DATE OF BIRTH July 11, 1732
PLACE OF BIRTH Bourg-en-Bresse , France
DATE OF DEATH April 4, 1807
Place of death Paris