ome. He stated that, from his
great age and infirmities, Galileo's career was near its close; that he
possessed many valuable ideas, which the world might lose if they were
not matured and conveyed to his friends; and that Galileo was anxious to
make these communications to Father Castelli, who was then a stipendiary
of the Court of Rome. The Grand Duke commanded his ambassador to see
Castelli on the subject--to urge him to obtain leave from the Pope to
spend a few months in Florence--and to supply him with money and every
thing that was necessary for his journey. Influenced by this kind and
liberal message, Castelli obtained an audience of the Pope, and
requested leave to pay a visit to Florence. Urban instantly suspected
the object of his journey; and, upon Castelli's acknowledging that he
could not possibly refrain from seeing Galileo, he received permission
to visit him in the company of an officer of the Inquisition. Castelli
accordingly went to Florence, and, a few months afterwards, Galileo was
ordered to return to Arcetri.

During Galileo's confinement at Sienna and Arcetri, between 1633 and
1638, his time was principally occupied in the composition of his
"Dialogues on Local Motion," in which he treats of the strength and
cohesion of solid bodies, of the laws of uniform and accelerated
motions, of the motion of projectiles, and of the centre of gravity of
solids. This remarkable work, which was considered by its author as the
best of his productions, was printed by Louis Elzevir, at Amsterdam, and
dedicated to the Count de Noailles, the French ambassador at Rome.
Various attempts to have it printed in Germany had failed; and, in order
to save himself from the malignity of his enemies, he was obliged to
pretend that the edition published in Holland had been printed from a
MS. entrusted to the French ambassador.

Although Galileo had for a long time abandoned his astronomical studies,
yet his attention was directed, about the year 1636, to a curious
appearance in the lunar disc, which is known by the name of the moon's
libration. When we examine with a telescope the outline of the moon, we
observe that certain parts of her disc, which are seen at one time, are
invisible at another. This change or libration is of four different
kinds, viz. the diurnal libration, the libration in longitude, the
libration in latitude, and the spheroidal libration. Galileo discovered
the first of these kinds of libration, and appear