A History of Science, vol 3 | Page 9

incorrectly measured by his patron in 1684. This was begun in 1739,
and occupied him for two years before successfully completed. As a
reward, however, he was admitted to the academy and appointed
mathematical professor in Mazarin College.
In 1751 he went to the Cape of Good Hope for the purpose of
determining the sun's parallax by observations of the parallaxes of Mars
and Venus, and incidentally to make observations on the other southern
hemisphere stars. The results of this undertaking were most successful,
and were given in his Coelum australe stelligerum, etc., published in
1763. In this he shows that in the course of a single year he had
observed some ten thousand stars, and computed the places of one
thousand nine hundred and forty-two of them, measured a degree of the
meridian, and made many observations of the moon--productive
industry seldom equalled in a single year in any field. These
observations were of great service to the astronomers, as they afforded
the opportunity of comparing the stars of the southern hemisphere with
those of the northern, which were being observed simultaneously by
Lelande at Berlin.
Lacaille's observations followed closely upon the determination of an
absorbing question which occupied the attention of the astronomers in
the early part of the century. This question was as to the shape of the
earth--whether it was actually flattened at the poles. To settle this
question once for all the Academy of Sciences decided to make the
actual measurement of the length of two degrees, one as near the pole
as possible, the other at the equator. Accordingly, three astronomers,
Godin, Bouguer, and La Condamine, made the journey to a spot on the
equator in Peru, while four astronomers, Camus, Clairaut, Maupertuis,
and Lemonnier, made a voyage to a place selected in Lapland. The
result of these expeditions was the determination that the globe is
oblately spheroidal.
A great contemporary and fellow-countryman of Lacaille was Jean Le
Rond d'Alembert (1717-1783), who, although not primarily an
astronomer, did so much with his mathematical calculations to aid that

science that his name is closely connected with its progress during the
eighteenth century. D'Alembert, who became one of the best-known
men of science of his day, and whose services were eagerly sought by
the rulers of Europe, began life as a foundling, having been exposed in
one of the markets of Paris. The sickly infant was adopted and cared for
in the family of a poor glazier, and treated as a member of the family.
In later years, however, after the foundling had become famous
throughout Europe, his mother, Madame Tencin, sent for him, and
acknowledged her relationship. It is more than likely that the great
philosopher believed her story, but if so he did not allow her the
satisfaction of knowing his belief, declaring always that Madame
Tencin could "not be nearer than a step-mother to him, since his mother
was the wife of the glazier."
D'Alembert did much for the cause of science by his example as well as
by his discoveries. By living a plain but honest life, declining
magnificent offers of positions from royal patrons, at the same time
refusing to grovel before nobility, he set a worthy example to other
philosophers whose cringing and pusillanimous attitude towards
persons of wealth or position had hitherto earned them the contempt of
the upper classes.
His direct additions to astronomy are several, among others the
determination of the mutation of the axis of the earth. He also
determined the ratio of the attractive forces of the sun and moon, which
he found to be about as seven to three. From this he reached the
conclusion that the earth must be seventy times greater than the moon.
The first two volumes of his Researches on the Systems of the World,
published in 1754, are largely devoted to mathematical and
astronomical problems, many of them of little importance now, but of
great interest to astronomers at that time.
Another great contemporary of D'Alembert, whose name is closely
associated and frequently confounded with his, was Jean Baptiste
Joseph Delambre (1749- 1822). More fortunate in birth as also in his
educational advantages, Delambre as a youth began his studies under
the celebrated poet Delille. Later he was obliged to struggle against
poverty, supporting himself for a time by making translations from
Latin, Greek, Italian, and English, and acting as tutor in private families.
The turning-point of his fortune came when the attention of Lalande

was called to the young man by his remarkable memory, and Lalande
soon showed his admiration by giving Delambre certain difficult
astronomical problems to solve. By performing these tasks successfully
his future as an astronomer became assured. At that time the planet
Uranus had just been discovered by Herschel, and the Academy of
Sciences offered as