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 prominence.