Nicolas Louis de Lacaille : biography

Abbé Nicolas Louis de Lacaille ( 28 December 1713 – 21 March 1762)Thomas Hockey et al: The Biographical Dictionary of Astronomers, Springer, 2007, ISBN 978-0-387-31022-0, p665 was a French astronomer. Note that the birth date given that of his baptism; babies were normally baptised on the day that they were born. Almost certainly the traditional date of 15 March 1713 is incorrect.

He is noted for his catalogue of nearly 10,000 southern stars, including 42 nebulous objects. This catalogue, called Coelum Australe Stelliferum, was published posthumously in 1763. It introduced 14 new constellations which have since become standard. He also calculated a table of eclipses for 1800 years.

In honor of his contribution to the study of the southern hemisphere sky, a 60-cm telescope at Reunion Island will be named the La Caille Telescope.(French)

Biography

Born at Rumigny (in present-day Ardennes), he attended school in Mantes-sur-Seine (now Mantes-la-Jolie). Afterwards he studied rhetoric and philosophy at the Collège de Lisieux and then theology at the Collège de Navarre. He was left destitute in 1731 by the death of his father, who had held a post in the household of the duchess of Vendôme. However he was supported in his studies by the Duc de Bourbon, his father’s former patron.

After he had taken deacon’s orders, however, he concentrated on science, and, through the patronage of Jacques Cassini, obtained employment, first in surveying the coast from Nantes to Bayonne, then, in 1739, in remeasuring the French arc of the meridian, for which he is honored with a pyramid at Juvisy-sur-Orge. The success of this difficult operation, which occupied two years, and achieved the correction of the anomalous result published by J. Cassini in 1718, was mainly due to Lacaille’s industry and skill. He was rewarded by admission to the Academy and the appointment of mathematical professor in Mazarin college, where he worked in a small observatory fitted for his use.

His desire to observe the southern heavens led him to propose, in 1750, an astronomical expedition to the Cape of Good Hope. This was officially sanctioned by Roland-Michel Barrin de La Galissonière. Among its results were determinations of the lunar and of the solar parallax (Mars serving as an intermediary), the first measurement of a South African arc of the meridian, and the observation of 10,000 southern stars. On his return to Paris in 1754 Lacaille was distressed to find himself an object of public attention; he withdrew to Mazarin college, where he worked actively for some years, and there died of an attack of gout aggravated by over-work in 1762.

Lalande said of him that, during a comparatively short life, he had made more observations and calculations than all the astronomers of his time put together. The quality of his work rivalled its quantity, while the disinterestedness and rectitude of his moral character earned him universal respect.

In 1754, de Lacaille was elected a foreign member of the Royal Swedish Academy of Sciences. He was also elected an honorary member of the academies of Saint Petersburg and Berlin, the Royal Society of London and the Royal Society of Göttingen, and the Institute of Bologna.Thomas Hockey et al: The Biographical Dictionary of Astronomers, Springer, 2007, ISBN 978-0-387-31022-0, p666

The crater La Caille on the Moon is named after him. Asteroid 9135 Lacaille (AKA 7609 P-L and 1994 EK6), discovered on 17 October 1960 by Cornelis Johannes van Houten, Ingrid van Houten-Groeneveld and Tom Gehrels at Palomar Observatory, was also named after him.

Notes

Measuring the southern arc of meridian

At the Cape, Abbé de Lacaille wanted to test Newton’s theory of gravitation and verify the shape of the earth in the southern hemisphere. He set out a baseline north of Darling. Using triangulation he then measured a 137 km arc of meridian between Cape Town and Aurora. The results suggested the earth was egg-shaped rather than oval. In 1838, Thomas Maclear who was Astronomer Royal at the Cape, repeated the measurements. He found that de Lacaille had failed to take into account the gravitational attraction of the nearby mountains.

Main works

• Astronomiae Fundamenta (1757), containing a standard catalogue of 398 stars, re-edited by F. Baily (Memoirs Roy. Astr. Society, v. 93)
• Tabulae Solares (1758)
• (1763) (edited by J. D. Maraldi), giving zone observations of 10,000 stars, and describing fourteen new constellations
• Observations sur 515 étoiles du Zodiaque (published in t. vi. of his Ephémérides, 1763)
• Leçons élémentaires de Mathématiques (1741), frequently reprinted
• ditto de Mécanique (1743), &c.
• ditto d’Astronomie (1746), 4th edition augmented by Lalande (1779)
• ditto d’Optique (1750), &c.
• Calculations by him of eclipses for eighteen hundred years were inserted in L’Art de vérifier les dates by Benedictine historian Charles Clémencet (1750)
• He communicated to the Academy in 1755 a classed catalogue of forty two southern nebulae, in and gave in t. ii. of his Ephémérides (1755) practical rules for the employment of the lunar method of longitudes, proposing in his additions to Pierre Bouguer’s Traité de Navigation (1760) the model of a nautical almanac.