across the channel were by no means idle. In France several successful
observers were making many additions to the already long list of observations
of the first astronomer of the Royal Observatory of Paris, Dominic Cassini
(1625-1712), whose reputation among his contemporaries was much greater
than among succeeding generations of astronomers. Perhaps the most deserving
of these successors was Nicolas Louis de Lacaille (1713-1762), a theologian
who had been educated at the expense of the Duke of Bourbon, and who, soon
after completing his clerical studies, came under the patronage of Cassini,
whose attention had been called to the young man's interest in the sciences.
One of Lacaille's first under-takings was the remeasuring of the French
are of the meridian, which had been 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 the subject for one
of its prizes the determination of the planet's orbit. Delambre made this
determination and won the prize - a feat that brought him at once into
By his writings he probably did as much
towards perfecting modern astronomy as any one man. His History of Astronomy
is not merely a narrative of progress of astronomy but a complete abstract
of all the celebrated works written on the subject. Thus he became famous
as an historian as well as an astronomer.