ii. p. 121.

It appears, on the testimony of Galileo himself, that he taught the
Ptolemaic system, in compliance with the popular feeling, after he had
convinced himself of the truth of the Copernican doctrines. In the
treatise on the sphere, indeed, which bears his name,[7] and which must
have been written soon after he went to Padua, and subsequently to 1592,
the stability of the earth, and the motion of the sun, are supported by
the very arguments which Galileo afterwards ridiculed; but we have no
means of determining whether or not he had then adopted the true system
of the universe. Although he might have taught the Ptolemaic system in
his lectures after he had convinced himself of its falsehood, yet it is
not likely that he would go so far as to publish to the world, as true,
the very doctrines which he despised. In a letter to Kepler, dated in
1597, he distinctly states that he _had, many years ago, adopted the
opinions of Copernicus_; but that _he had not yet dared to publish his
arguments in favour of them, and his refutation of the opposite
opinions_. These facts would leave us to place Galileo's conversion
somewhere between 1593 and 1597, although _many_ years cannot be said
to have elapsed between these two dates.

[7] The authenticity of this work has been doubted. It was printed
at Rome, in 1656, from a MS. in the library of Somaschi, at Venice.
See Opere di Galileo, tom. vii. p. 427.

At this early period of Galileo's life, in the year 1593, he met with an
accident which had nearly proved fatal. A party at Padua, of which he
was one, were enjoying, at an open window, a current of air, which was
artificially cooled by a fall of water. Galileo unfortunately fell
asleep under its influence; and so powerful was its effect upon his
robust constitution, that he contracted a severe chronic disorder,
accompanied with acute pains in his body, and loss of sleep and
appetite, which attacked him at intervals during the rest of his life.
Others of the party suffered still more severely, and perished by their
own rashness.

Galileo's reputation was now widely extended over Europe. The Archduke
Ferdinand (afterwards Emperor of Germany), the Landgrave of Hesse, and
the Princes of Alsace and Mantua, honoured his lectures with their
presence; and Prince Gustavus Adolphus of Sweden also received
instructions from him in mathematics, during his sojourn in Italy.

When Galileo had completed the first peri