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GALILEI, GALILEO (b. Pisa, Italy, 15 February
1564; d. Arcetri, Italy, 8 January 1642), physics,
astronomy.
assumed proportionality of speed to space traversed.
Accordingly, he introduced in its place two propositions
drawn from mechanics, which he submitted for
criticism to Valerio. Galileo received Valerio's reply
in July 1609, just after his attention had again been
diverted from mechanics, this time by news of the
invention of the telescope.
The Telescope.
A Dutch lens-grinder, Hans Lipperhey,
had applied in October 1608 to Count
Maurice of Nassau for a patent on a device to make
distant objects appear closer. Sarpi, whose extensive
correspondence (maintained for theological and political
reasons) kept him currently informed, learned
of this device within a month. Somewhat skeptical,
he applied for further information to Jacques
Badovere (Giacomo Badoer), a former pupil of Galileo's
then at Paris. In due course the report was
confirmed. Galileo heard discussions of the news
during a visit to Venice in July 1609, learned from
Sarpi that the device was real, and probably heard
of the simultaneous arrival at Padua of a foreigner
who had brought one to Italy. He hastened back to
Padua, found that the foreigner had left for Venice,
and at once attempted to construct such a device
himself. In this he quickly succeeded, sent word of
it to Sarpi, and applied himself to the improvement
of the instrument. Sarpi, who had meanwhile been
selected by the Venetian government to assess the
value of the device offered for sale to them by the
stranger, discouraged its purchase. Late in August,
Galileo arrived at Venice with a nine-power telescope,
three times as effective as the other. The practical
value of this instrument to a maritime power obtained
for him a lifetime appointment to the university, with
an unprecedented salary for the chair of mathematics.
The official document he received, however, did not
conform to his understanding of the terms he had
accepted. As a result, he pressed his application for
a post at the Tuscan court, begun a year or two earlier.
Galileo's swift improvement of the telescope continued
until, at the end of 1609, he had one of about
thirty power. This was the practicable limit for a
telescope of the Galilean type, with plano-convex
objective and plano-concave eyepiece. He turned this
new instrument to the skies early in January 1610,
with startling results. Not only was the moon revealed
to be mountainous and the Milky Way to be a congeries
of separate stars, contrary to Aristotelian principles,
but a host of new fixed stars and four satellites
of Jupiter were promptly discovered. Working with
great haste but impressive accuracy, Galileo recited
these discoveries in the Sidereus nuncius, published
at Venice early in March 1610.
His sudden fame assisted Galileo in his negotiations
at Florence. Moreover, the new discoveries made him
reluctant to continue teaching the old astronomy. In
the summer of 1610, he resigned the chair at Padua
and returned to Florence as mathematician and philosopher
to the grand duke of Tuscany, and chief
mathematician of the University of Pisa, without
obligation to teach.
Galileo's book created excitement throughout
Europe and a second edition was published in the
same year at Frankfurt. Kepler endorsed it in two
small books, the Dissertatio cum Nuncio Sidereo,
published before he had personally observed the new
phenomena, and the Narratio de observatis a se
quatuor Jovis satellitibus, published a few months
later. Other writers attacked the claimed discoveries
as a fraud. Galileo did not enter the controversy but
applied himself to further observations. He discovered,
later in 1610, the oval appearance of Saturn
and the phases of Venus. His telescope was inadequate
to resolve Saturn's rings, which he took to be
satellites very close to the planet. The phases of Venus
removed a serious objection to the Copernican system,
and he saw in the satellites of Jupiter a miniature
planetary system in which, as in the Copernican astronomy,
it could no longer be held that all moving
heavenly bodies revolved exclusively about the earth.
Early in 1611 Galileo journeyed to Rome to exhibit
his telescopic discoveries. The Jesuits of the Roman
College, who had at first been dubious, confirmed
them and honored Galileo. Federico Cesi feted Galileo
and made him a member of the Lincean Academy,
the first truly scientific academy, founded in
1603. The pope and several cardinals also showed
their esteem for Galileo.
Controversies at Florence.
Shortly after his return
to Florence, Galileo became involved in a controversy
over floating bodies. In that controversy an important
role was played by Colombe, who became the leader
of a group of dissident professors and intriguing
courtiers that resented Galileo's position at court.
Maffeo Barberini—then a cardinal but later to become
pope—took Galileo's side in the dispute. Turning
again to physics, Galileo composed and published
a book on the behavior of bodies placed in water
(Discurso ... intorno alle cose che stanno in su
l'acqua, o in quella si muovono), in support of Archimedes
and against Aristotle, of which two editions
appeared in 1612. Using the concept of moment and
the principle of virtual velocities, Galileo extended
the scope of the Archimedean work beyond purely
hydrostatic considerations.
While this work was in progress, Galileo received
from Marcus Welser of Augsburg a short treatise on
sunspots that Welser had published pseudonymously