Nicolas-Louis de Lacaille

Lore & Background

Lacaille was born at Rumigny in the Ardennes in eastern France and attended school in Mantes-sur-Seine. He studied rhetoric and philosophy at the Collège de Lisieux and theology at the Collège de Navarre. Left destitute in 1731 by his father's death, he was supported by the Duc de Bourbon. He took deacon's orders, becoming an Abbé, and concentrated on science. Through Jacques Cassini's patronage, he surveyed the coast from Nantes to Bayonne and in 1739 remeasured the French meridian arc, correcting an anomalous result published by Jacques Cassini in 1718. He was admitted to the Royal Academy of Sciences and appointed professor of mathematics at the Mazarin college of the University of Paris, where he built a small observatory. His students included Antoine Lavoisier and Jean Sylvain Bailly.

Reader's Guide

Lacaille's significance lies in his systematic survey of the southern sky, which produced the Coelum Australe Stelliferum catalogue and introduced 14 constellations that remain standard. His arc measurement at the Cape of Good Hope, though initially suggesting a prolate Earth, was later corrected by Thomas Maclear, who confirmed George Everest's conjecture that gravitational deflection of the vertical had affected Lacaille's latitude observations. Lacaille also prepared the first accurate lunar tables for determining longitude via lunar distances, and calculated a table of eclipses for 1,800 years. His work advanced positional astronomy and geodesy, and his textbooks and advocacy of Newtonian theory influenced a generation of scientists. The crater 'La Caille' on the Moon and asteroid 9135 Lacaille commemorate his contributions.

Did You Know?

• Lacaille named 14 constellations, including Mensa, the only one named after a terrestrial feature (Table Mountain).
• He observed over 10,000 stars using a refracting telescope during his 1750–1754 stay at the Cape of Good Hope.
• His arc measurement at the Cape suggested the Earth was lengthened (prolate) toward the south pole, later corrected by Thomas Maclear.
• The comet now known as Halley's Comet was named after Edmond Halley, not by Lacaille.