He concentrated thereafter 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 meridian arc, for which he is honoured 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 Jacques Cassini in 1718, was mainly due to Lacaille's industry and skill.

He was rewarded by admission to the Royal Academy of Sciences and appointment as Professor of mathematics in the Mazarin college of the University of Paris, where he constructed a small observatory fitted for his own use.

His desire to determine the distances of the planets trigonometrically, using the longest possible baseline, led him to propose, in 1750, an expedition to the Cape of Good Hope.

Using triangulation he then measured a 137 km arc of meridian between Cape Town and Aurora, determining the astronomical latitudes of the end points by means of astronomical-geodetic observations.

[11] During his voyage to the southern hemisphere as a passenger on the vessel Le Glorieux, captained by the noted hydrographer Jean-Baptiste d'Après de Mannevillette, Lacaille became conscious of the difficulties in determining positions at sea.

On his return to Paris he prepared the first set of tables of the Moon's position that was accurate enough to use for determining time and longitude by the method of 'Lunars' (Lunar distances) using the orbital theory of Clairaut.

The quality of his work rivalled its quantity, while the disinterestedness and rectitude of his moral character earned him universal respect.

In 1757 he published his Astronomiae Fundamenta Novissimus, containing a list of about 400 bright stars with positions corrected for aberration and nutation.

His last public lecture, given on 14 September 1761 at the Royal Academy of Sciences, summarised the improvements to astronomy that had occurred during his lifetime, to which he had made no small contribution.