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GALILEI, GALILEO (b. Pisa, Italy, 15 February
1564; d. Arcetri, Italy, 8 January 1642), physics,
and a common outlook rather than from early and
direct knowledge of Benedetti's work.
Similarly, a direct influence of medieval writers on
Galileo, although widely accepted by most historians,
is still largely conjectured on the basis of specific
parallels. The statics of Jordanus de Nemore was
widely known in Italy after 1546, when Tartaglia
published in Italian and endorsed the “science of
weights” as necessary to an understanding of the
balance; yet all subsequent writers (at least in Italy)
condemned it in favor of the Archimedean approach.
Writings of the Merton school, published repeatedly
in Italy up to about 1520, continued to be discussed
thereafter at Paris and in Spain. Galileo's reasoning
about acceleration, after his recognition of its importance
around 1602, invariably proceeded by comparison
of ratios, whereas medieval writers adopted a
mean speed as representative of uniformly changing
velocities. Medieval impetus theory, which Galileo
adopted at first for the explanation of projectile motion,
had no place in the concept of neutral motions
that led him eventually to an inertial terrestrial physics.
A connection of Galileo's own physical thought
with medieval sources may yet be convincingly
established, but at present this has not been done.
Experiment and Mathematics.
The role of experiment
in Galileo's physics was limited to the testing
of preconceived mathematical rules and did not extend
to the systematic search for such rules. It is
probable that his use of experiment had its roots in
the musical controversy conducted by his father
rather than in philosophical considerations of method.
Appeal to experiment in his published works was
resorted to by Galileo chiefly as a means of confuting
rival theories, as in the dispute over bodies in water
and in his rejection of proportionality of speed to
space traversed in free fall.
It is difficult to find older sources for Galileo's
attitude toward mathematics, which was strikingly
modern. He considered mathematics to enjoy a superior
certainty over logic. Where a mathematical relation
could be found in nature, Galileo accepted it
as a valid description and discouraged further search
for ulterior causes. He attributed discrepancies between
mathematics and physical events to the investigator
who did not yet know how to balance his
books. Galileo did not adopt the traditional Platonist
view that our world is a defective copy of the “real”
world, and he derided philosophical speculation about
a world on paper.
The Influence of Galileo.
Except with respect to the
acceptance of Copernican astronomy, Galileo's direct
influence on science outside Italy was probably not
very great. After 1610 he published his books in
Italian and made little effort to persuade professional
scholars either at home or abroad. His influence on
educated laymen both in Italy and abroad was considerable;
on university professors, except for a few
who were his own pupils, it was negligible. Latin
translations of his Dialogue appeared in Holland in
1635, in France in 1641, and in England in 1663; but
the only Latin translation of the Two New Sciences
was published in 1700, long after Newton's Principia
had superseded it.
Between Galileo and Newton, science was Cartesian
rather than Galilean. Indirectly, Galileo's science
exerted some influence in France through Marin
Mersenne, Pierre Gassendi, and Nicholas Fabri de
Peiresc; in Germany through Kepler; and in England
through John Wilkins and John Wallis. Descartes,
who repudiated Galileo's approach to physics because
of its neglect of the essence of motion and physical
causation, did not mention him in any published
work. Newton seems not to have read Galileo's Two
New Sciences, at least not before 1700, but knew his
Dialogue as early as 1666. Aware of his achievements
in physics only indirectly, Newton, in the Principia,
mistakenly credited Galileo with a derivation of the
laws of falling bodies from the law of inertia and the
Within Italy, Galileo had a strong following both
in scientific and nonscientific circles. His ablest pupil,
Castelli, was the teacher of Torricelli and Cavalieri,
both of whom also had personal acquaintance with
Galileo. His last pupil, Viviani, did much to extend
Galileo's influence in the succeeding generation,
editing the first collection of his works in 1655-1656.
But by that time physics and astronomy had both
progressed well beyond the point where Galileo had
Outside scientific circles, Galileo's influence was
strongly felt in the battle for freedom of inquiry and
against authority. English translations of his Dialogue
and Letter to Christina, published in 1661, carried this
influence outside academic circles. John Milton cited
the fate of Galileo in his Areopagitica. French writers
during the Enlightenment also made Galileo a symbol
of religious persecution.
Galileo was of average stature,
squarely built, and of lively appearance and disposition.
Viviani remarks that he was quick to anger and
as quickly mollified. His unusual talents as a speaker
and as a teacher are beyond question. Among those
who knew him personally, even including adversaries,
few seem to have disliked him. Many distinguished
men became his devoted friends, and some sacrificed
their own interests in his support at crucial periods.
On the other hand, there were many contemporary