l 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 prominence.

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.

LEONARD EULER

Still another contemporary of D'Alembert and Delambre, and somewhat
older than either of them, was Leonard Euler (1707-1783), of Basel,
whose fame as a philosopher equals that of either of the great
Frenchmen. He is of particular interest here in his capacity of
astro