Jérôme Lalande | |
|---|---|
 Jérôme de La Lande byJean-Honoré Fragonard,c. 1769 | |
| Born | (1732-07-11)11 July 1732 |
| Died | 4 April 1807(1807-04-04) (aged 74) |
| Scientific career | |
| Fields | Astronomy |
| Institutions | Paris observatory |
| Doctoral advisor | Joseph-Nicolas Delisle Pierre Charles Le Monnier |
| Doctoral students | Jean Baptiste Joseph Delambre |
Joseph Jérôme Lefrançois de Lalande (French:[lalɑ̃d]; 11 July 1732 – 4 April 1807) was a Frenchastronomer,freemason and writer. He is known for having estimated a precise value of theastronomical unit (the distance from theEarth to theSun) using measurements of thetransit of Venus in 1769.
Lalande was born atBourg-en-Bresse (département ofAin) to Pierre Lefrançois and Marie‐Anne‐Gabrielle Monchinet.[1] His parents sent him to Paris to study law, but as a result of lodging in the Hôtel Cluny, whereJoseph-Nicolas Delisle had his observatory, he was drawn to astronomy, and became the zealous and favoured pupil of both Delisle andPierre Charles Le Monnier. Having completed his legal studies, he was about to return to Bourg to practise as an advocate, when Le Monnier obtained permission to send him toBerlin, to make observations on the lunarparallax in concert with those ofNicolas Louis de Lacaille at theCape of Good Hope.[2]
The successful execution of this task obtained for him, before he was twenty-one, admission to theAcademy of Berlin, as well as his election as an adjunct astronomer to theFrench Academy of Sciences. He now devoted himself to the improvement of the planetary theory, publishing in 1759 a corrected edition ofEdmond Halley's tables, with a history ofHalley's Comet whose return in that year he had helpedAlexis Clairaut andNicole-Reine Lepaute to calculate.[3] In 1762, Delisle resigned the chair of astronomy in the Collège de France in Lalande's favour. The duties were discharged by Lalande for forty-six years. His house became an astronomical seminary, and amongst his pupils wereJean Baptiste Joseph Delambre,Giuseppe Piazzi,Pierre Méchain, and his own nephewMichel Lefrançois de Lalande. By his publications in connection with thetransit of Venus of 1769 he won great fame. However, his difficult personality lost him some popularity.[2]
In 1766, Lalande, withClaude Adrien Helvétius, founded theLes Sciences lodge in Paris, and received its recognition fromGrand Orient de France in 1772.[4] In 1776, he changed its name toLes Neuf Soeurs, and arranged forBenjamin Franklin to be chosen as the first worshipful master.[5]
Although his investigations were conducted with diligence rather than genius, Lalande's career was an eminent one. As a lecturer and writer he helped popularise astronomy. His planetary tables, into which he introduced corrections for mutual perturbations, were the best available up to the end of the 18th century. In 1801, he endowed theLalande Prize, administered by theFrench Academy of Sciences, for advances in astronomy.Pierre-Antoine Véron, the young astronomer who for the first time in history determined the size of the Pacific Ocean from east to west, was Lalande's disciple.[6]
Lalande was an atheist,[7] and wrote a dictionary of atheists with supplements that appeared in print posthumously.
He never married. He was believed to have an illegitimate daughterMarie-Jeanne de Lalande whom he trained in mathematics so that she could help him with his work;[8] according to more recent research she was not his daughter.[9]
In February 1847Sears C. Walker of theUS Naval Observatory was searching historical records and surveys for possible prediscovery sightings of the planetNeptune that had been discovered the year before. He found that observations made by Lalande's nephew,Michel Lefrançois de Lalande in 1795 were in the direction of Neptune's position in the sky at that time and that Neptune might appear in the observation records. On 8 May and again on 10 May 1795 astar was observed and recorded with uncertainty noted on its position with a colon, this notation could also indicate an observing error so it was not until the original records of the observatory were reviewed that it was established with certainty that the object was Neptune and the position error between the two nights was due to the planet's motion across the sky.[10] The discovery of these records of Neptune's position in 1795 led to a better calculation of the planet's orbit.[11]
His published works include:[2]
He communicated more than one hundred and fifty papers to theFrench Academy of Sciences, edited theConnoissance de temps (1759–1774), and again (1794–1807), and wrote the concluding two volumes of the 2nd edition ofMontucla'sHistoire des mathématiques (1802).[2]
Attribution
This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Lalande, Joseph Jérôme Lefrançais de".Encyclopædia Britannica. Vol. 16 (11th ed.). Cambridge University Press. p. 95.
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