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Lacaille was the first to catalogue the star clusters and nebulae in the far southern sky.

LIFE SKETCH OF LACAILLE
(https://upload.wikimedia.org/wikiped...a/Lacaille.jpg)
The biographical information on Lacaille’s life was principally obtained from the book
Lacaille: Astronomer, Traveler, by David S Evans.

Previous to Nicolas-Louis de La Caille work, Edmond Halley (1656 – 1742) catalogued 341 stars from the island of St Helena in the South Atlantic Ocean in 1677. Halley’s interest was not just astronomy, it also included finding accurate time for navigation at sea. His star catalogue was designed to help in this regard.

In 1714 the British Board for the Discovery of Longitude offered prize money of £20,000 for an accurate method for measuring east west longitude at sea. Although Evans indicates that Lacaille was not interested in personal wealth, this prize may have provided some impetus for Lacaille. For the next 47 years there was competition amongst astronomers until the money was finally awarded.

Lacaille’s father, Charles Lewis La Caille (1679-1731) and his mother Barbe Rebuy had 10
children, 6 daughters and 4 sons. Six children died young, three girls and three boys. The other
3 girls become nuns and Nicolas-Louis became an astronomer.

(Lacaille monument at Rumigny. https://maps.app.goo.gl/nMKSVXYkKtM7RTGq5)
Nicolas-Louis de La Caille was born in March or December 1713 at Rumigny (195 km NE of Paris), France. His education began with his mechanically minded father tutoring him. At age sixteen, Nicolas-Louis attended the college of Mantes-sur-Seine, where he studied humanities. He studied rhetoric for the next two years in Paris, but his interests included history, antiquities, mythology and Latin poetry. His father’s death in 1731, when he was eighteen, left Nicolas-Louis with large debts.

After completing his philosophical studies in Paris, he went on to three years of theology, intending to become a priest. It was during his theological studies that Lacaille became interested in mathematics, especially Euclid’s Elements, which he studied on his own. He also taught himself astronomy. Lacaille passed his examinations with distinction, but when he failed to answer the Vice-Chancellor’s questions satisfactorily, he was denied his Master of Arts, and this turned him from theology. He was never ordained.

Lacaille spent the next year at Paris Observatory working with Cassini II and Maraldi II. For
some reason, Lacaille lost the esteem of Cassini II, but in July 1739, Lacaille and Cassini III
began a geodetic survey of a 930 km long meridian from Perpignan, on the French
Mediterranean Coast (near Spain) to Dunkirk on the English Channel, to establish the
circumference of the earth.

Later Lacaille moved to the Collège Mazarin where he studied the earth’s orbit, parallaxes, planetary orbits, comets and stars. He also wrote textbooks on mathematics, practical astronomy, mechanics and optics for the college. It was during this time that Lacaille became interested in the work of Father Feuillée who observed from the Canary Islands in 1724. This probably inspired his later trip to the Cape of Good Hope.

LACAILLE’S WORK IN THE SOUTHERN HEMISPHERE, 1751-1754

Lacaille set himself several goals for his stay in the southern hemisphere.
* He wanted to find the exact positions of the fixed stars, especially first, second and third magnitude stars near the ecliptic;
* the length of a simple seconds pendulum to provide a value for gravity at that location and hence information on the shape of the Earth;
* the longitude and latitude of important places, especially Cape Town;
* measure an arc of the meridian; and
* measure the parallaxes of the Moon, Mars and Venus which he did in conjunction with astronomers in Europe. Lacaille made plans with other astronomers for simultaneous observations of solar
system objects to determine their distances from the Earth, before he left for the Cape.

The authorities at the Cape were reluctant at first to allow Lacaille to observe there, because he
was a French Catholic, while they were Dutch Protestants. Previously there were problems with
a German astronomer, Peter Kolbe who invented false stories against these authorities.

Lacaille left Paris on October 20, 1750 and sailed from L’Orient on November 21 on the ship Le Glorieux. His trip was to span three years and eight months. The ship was uncertain of its position on the way from France to Africa, but a lunar eclipse on December 13, 1750 (totality from 5:32 to 7:11 UT) showed they were 4 degrees off course. They stayed at Rio de Janeiro from January 25 to February 25, 1751 where Lacaille did experiments on magnetism and pendulums. He also determined Rio de Janeiro’s longitude using the moon’s position with respect to the stars as an accurate clock.

Le Glorieux arrived off Cape Town on April 19, and Lacaille presented himself to the governor the next day. A leading citizen by the name of Bestbier gave Lacaille the use of his house. He spent the next six weeks in May and June constructing an observatory.

LACAILLE’S CAPE TOWN OBSERVATORY

Lacaille’s observatory was at the lower end of Strand St, in Cape Town behind Jan Lourens
Bestbier’s house. The governor, Ryk Tulbagh helped with the building of the observatory, which was only 2.5 metres above sea level.
(Lacaille’s observatory was here. https://maps.app.goo.gl/Epu1gxKoGEASMGXk7)

The observatory was a 4.1 m square with the corners pointing north, east, south and west. The sector was placed on the western pedestal, the quadrant on the northern pedestal and the sextant on the eastern pedestal. A bed, table and chairs filled the southern part of the crowded room. The door was near the southern corner on the western side and there was a window in the southeast wall. The wooden roof was covered with a tarpaulin.

INSTRUMENTS IN LACAILLE’S OBSERVATORY

The instruments used in Lacaille’s observatory are listed below:
1. A sector, with 1.95 m radius.
2. A sextant, with 1.95 m radius, which was equipped with two telescopes perpendicular
to each other. The focal lengths of the telescopes were 2.11 m and 1.79 m.
3. A quadrant, of 0.97 m radius with a 13.5 mm aperture refractor telescope attached. This was the main instrument used for the star catalogue.
4. A sidereal clock made by Julien le Roy.
5. Telescopes of various sizes, with focal lengths 14, 15 and 18 feet. Unfortunately their
apertures are not known. The 14-foot telescope was used to examine parts of the Milky
Way and the Magellanic clouds.

Lacaille’s aim was to replace the catalogue of 341 southern stars made by Edmund Halley in
1677 with a better one. He used a quadrant telescope, 75.7 cm in length with a three degree field
of view to make his star catalogue. The observations for the star catalogue were made “with a
clock regulated to the revolutions of the stars and with a telescope equipped with different
reticles.”

This telescope had a length of 866 mm. It was applied parallel to the fixed telescope of a quadrant of 974 mm radius, very heavy and of a very solid construction. The object glass of the telescope had a focal length of 712 mm: its aperture was 13.5 mm. The focal length of the eyepiece was 88 mm to give the telescope an extended field, very clear, and free from parallaxes at its edges. The field was almost 3 degrees. This gave eight times magnification. An expert workman by the name of Poitevin maintained and modified the instruments.