Person: De Lacaille, Nicolas-Louis
Nicolas-Louis de Lacaille was a French astronomer and geodesist who catalogued the stars of the Southern Hemisphere and named 14 out of the 88 constellations.
Mathematical Profile (Excerpt):
- Most biographers agree on his birthday being 15 March 1713, though some sources mark his birthday on 14 December, closer to 29 December, the date of his baptism.
- They owned the castle of Cour-des-Prés, where Lacaille grew up.
- Being in charge of Lacaille's studies from a young age, he transmitted his passions to him.
- Nicolas-Louis Lacaille went to study at the Collège de Mantes-sur-Seine (now Mantes-la-Jolie), 48 km west of Paris, and then, in 1729, with a scholarship to the Parisian Collège de Lisieux.
- He went on to study theology at the Collège de Navarre, entering in 1732, intending at this stage to become a priest.
- During this time, Lacaille came across a copy of Euclid's Elements.
- He eventually decided to focus entirely on the former, but he did not forget his religious background.
- He had become a deacon, and acted as such first in Saint-Étienne-du-Mont and later in the chapel of Collège Mazarin.
- Through astronomy, Abbé Lacaille became friends with Jacques Cassini, then director of the Paris Observatory.
- Cassini's influence helped Lacaille improve in his astronomical observations.
- He also befriended Cassini's son, César-François (often called Cassini de Thury), and nephew, Jean-Dominique Maraldi.
- In 1735, Lacaille surveyed the French coast from Nantes to Bayonne, along with Maraldi.
- Lacaille started working in the Paris Observatory in May 1736, and stayed there until January 1740.
- In July 1739, along with Maraldi and Cassini de Thury, Lacaille began measuring the French meridian.
- The results were published in 1743 with the title La Méridienne de France vérifiée Ⓣ(The Meridian of France verified) under Cassini de Thury's name.
- Lacaille, however, had made all the calculations and was not happy that all he received was an acknowledgement of his help in the Preface.
- The measurements of the meridian confirmed Newton's idea that the Earth was a sphere flattened at the poles, as did the results from the expeditions sent to Peru and Lapland in 1735 and 1736.
- The Académie des Sciences recognised Lacaille's worth and elected him as an assistant astronomer on 3 May 1741, when he was only 28 years old.
- On 5 April 1745, he was elected associate astronomer, replacing Grandjean de Fouchy (who was appointed perpetual secretary).
- Descartes" erroneous theory of fluid vortices in a space filled with an ill-defined medium still held sway.
- Indeed, it can be said that Lacaille and the mathematicians who were his contemporaries in Paris were the true successors of Newton when it came to the development of celestial mechanics and physics as a whole.
- There, he published many textbooks based on his lectures in mathematics (Leçons de Mathématiques Ⓣ(Lessons in mathematics), 1741), in mechanics (Leçons de Mécanique Ⓣ(Lessons in mechanics), 1743), in astronomy (Leçons d'Astronomie géométrique et physique Ⓣ(Lessons in geometric and physical astronomy), 1746) and in optics (Leçons d'Optique Ⓣ(Lessons in optics), 1750).
- Abbé Lacaille would often sell these books to his students at half their prize, not interested in financial gain.
- Lacaille moved his observatory to Collège Mazarin, where a new one had been built for him, stopping his visits to the Paris Observatory by 1742.
- Indeed Bradley had been elected to the Academy of Sciences in July 1748.
- After receiving Bradley's paper, Lacaille adjusted all his own observations to allow for nutation.
- Lacaille proposed a project for improving the foundations of astronomy, revising solar theory, and forming a star catalogue, and he invited the other astronomers of the Academy to join him in this undertaking.
- Cold-shouldered by the Cassinis, treated with hostility by P C Le Monnier and Jean d'Alembert, he carried the project forward on his own, with a heroism that went beyond the mere courage of physical endurance.
- Indeed, one of Abbé Lacaille's greatest astronomical achievements was the cataloguing of the southern stars.
- On 20 November 1750 he embarked on the vessel Le Glorieux, commanded by d'Après de Mennevillette, a friend of Lacaille's.
- He headed to the Cape of Good Hope on a scientific expedition organised by the Académie des Sciences, set up at Lacaille's request.
- He arrived on 19 April 1751, after a detour to Rio de Janeiro.
- His observations, published in 1763 in Coelum Australe Stelliferum Ⓣ(Stars of the Southern skies), include 10,305 distinct stars, immediately superseding Halley's previous catalogue, which was much smaller and less accurate.
- He identified fourteen new constellations, which he named after scientific instruments: Telescopium, Microscopium, Apparatus Sculptoris, Fornax chemical, Horologium, Reticulus rhomboidalis, Pyxis nautica, Antlia pneumatica, Octanis, Circinus, Norma, and Mons Menae.
- He described these constellations in Table des Ascensions Droites et des Declinaisons Apparentes des Etoiles australes renfermées dans le tropique du Capricorne ...
- Ⓣ(Table of right ascents and apparent declinations of Southern stars enclosed by the Tropic of Capricorn ...) (1756).
- Lacaille narrated in detail his journey to the Cape in Journal historique de voyage au Cap de Bonne-Espérance par feu M l'abbé de La Caille ...
- Abbé Carlier edited this publication and added a description of Lacaille's life.
- Two hundred years later, R Raven-Hart translated this work into English and it was published as Travels at the Cape, 1751-53: an annotated translation of 'Journal historique du voyage fait au Cap de Bonne-Espérance ...' (1976).
- In 1751, while in the Cape, he made some observations of the Moon.
- Later, when put together with the observations carried out by Jérôme Lalande in Berlin at the same time, they allowed the astronomer to determine the lunar parallax.
- The latitudes of the end stations were measured using a zenith sector.
- The radius of the earth at 33 degrees south was found to be comparable to that at 45 degrees north in France, implying that the planet was somewhat pear-shaped.
- Sir George Everest explained in 1821 that Lacaille was in error due to the gravitational attraction of the nearby mountains, particularly Table Mountain.
- Sir Thomas Mclear later revised this measure between 1838 and 1847 and was able to confirm that the error was not due to measurement errors by Lacaille for his baseline and latitudes were remarkably accurate.
- Abbé Lacaille came back to Paris on 28 June 1754 and continued his research.
- He created a method to calculate the orbits of comets, he studied astronomical refraction and he published ephemerides and logarithmic tables, among other things.
- In 1757, he published Astronomiae Fundamenta Ⓣ(Fundamental astronomy), a catalogue of the 400 brightest stars that was far superior to any of its predecessors.
- It is of note that Lacaille did not sell the Astronomiae Fundamenta Ⓣ(Fundamental astronomy) commercially, but distributed copies to those interested, paying for the expenses himself.
- Since the Observatory at Collège Mazarin was not ideal for it, Lacaille went to Carrières, near Charenton, along other astronomers.
- He was elected a member of the Science Academies of St Petersburg, Berlin, Stockholm, London, Göttingen and Bologna.
- We mentioned above Lacaille correspondence with Bradley but he was certainly not the only astronomer with whom Lacaille corresponded.
- A disagreement concerning the corrections of refraction predicted by both astronomers leads them into a heated debate, in which each one defends stoutly his own observation instrument while casting suspicion on the instrument of the other.
- In this case Tobias Mayer was right; Lacaille never came to realise that the graduation of his sextant, although carefully verified, was defective.
- Lacaille continued working until his death at Collège Mazarin in 1762 due to a fatal attack of the gout certainly made worse due to over-work.
- It was not until Francis Baily produced a catalogue that was published by the British Association in 1847 that all of Lacaille's observations became known.
Born 15 March 1713, Rumigny-en-Thiérache, France. Died 21 March 1762, Paris, France.
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Thank you to the contributors under CC BY-SA 4.0!
Adapted from other CC BY-SA 4.0 Sources:
- O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive