GALILEI, GALILEO (b. Pisa, Italy, 15 February 1564; d. Arcetri, Italy, 8 January 1642), physics, astronomy.

    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 force-acceleration relationship.

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 left them.

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.

Personal Traits.

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