PHYSICS
65
PHYSICS
first Catholic astronomer to adopt the double test
imposed upon astronomical hypotheses by Tycho
Brahe, and to decide (15S1) that the suppositions
of Copernicus were to be rejected, as oppiisod Ixitli to
Peripatetic physics and to Scripture; on the ofiier
hand, at the end of his life and under the influence
of Galileo's discoveries, Clavius appeared to have
assumed a far more favourable attitude towards
Copernican doctrines. The enemies of Aristotelean
philosophy gladly adopted the system of Copernicus,
considering its hypotheses as so many propositions
physically true, this being the case with Pierre de La
Ram^e, called Petrus Ramus (1502-72), and espe-
cially with Giordano Bruno (about 1550-1600). The
physics developed by Bruno, in which he incorporated
the Copernican hypothesis, proceeded from Nicole,
Oresme, and Nicholas of Cusa; but chiefly from the
physics taught in the University of Paris in the four-
teenth century. The infinite extent of the universe
and the plurality of worlds were admitted as possible
by many theologians at the end of the thirteenth
century, and the theory of the slow motion which
gradually causes the central portions of the Earth
to work to the surface had been taught by Albert
of Saxony before it attracted the attention of Vinci.
The solution of Peripatetic arguments against the
Earth's motion and the theory of gravity called forth
by the comparison of the planets with the Earth
would appear to have been borrowed by Bruno from
Oresme. The apostasy and heresies for which Bruno
was condemned in 1600 had nothing to do with the
physical doctrines he had espoused, which included
in particular Copernican astronomy. In fact it
does not seem that, in the sixteenth century, the
Church manifested the slightest anxiety concerning
the system of Copernicus.
XIV. Theory of the Tides. — It is undoubtedly to the great voyages that shed additional lustre on the close of the fifteenth century that we must attribute the importance assumed in the sixteenth century by the problem of the tides, and the great progress made at that time towards the solution of this prob- lem. The correlation existing between the phenome- non of high and low tide and the course of the moon was known even in ancient times. Posidonius accu- rately described it; the Arabian astronomers were also familiar with it, and the explanation given of it in the ninth century by Albumazar in his "Intro- ductoriura magnum ad Astrononiiam " remained a classic throughout the Middle Ages. The observation of tidal phendiiifiui very naturally led to the supposi- tion that the iiKiiui attracted the waters of the ocean and, in the thirteenth century, William of Auvergne compared this attraction to that of the magnet for iron. However, the mere attraction of the moon did not suffice to account for the alternation of spring and neap tides, which jihenomenon clearly indicated a certain intervention of the sun. In his "Questions sur les livres des Meteores", which appeared during the latter half of the fourteenth century, Themon, "Son of the Jew", introduced in a vague sort of way the idea of superposing two tides, the one due to the sun and the other to the moon.
In l.^'JS this idea was very clearly endorsed by Federico Grisogone of Zara, a Dalmatian who taught medicine at Padua. Grisogone declared that, under the action of the moon exclusively, the sea would assume an ovoid shape, its major axis being directed towards the centre of the moon; that the action of the sun would also give it an ovoid shape, less elon- gated than the first, its major axis being directed toward.s the centre of the sun; and that the variation of sea level, at all times and in all places, was obtained by adding the elevation or depression produced by the solar tide to the elevation or depression produced by the lunar tide. In 15.57 Girolamo Cardano accepted and briefly explained Grisogone's theory.
In 15.59 a posthumous work by Delfino gave a de-
scription of the phenomena of the tides, identical with
that deduced from the mechanism conceived by
(irisogone. The doctrine of the Dalmatian physician
w;is reproduced by Paolo Gallucci in 1588, and by
Annibale Raimondo in 1589; and in 1600 Claude
Duret, who had plagiarized Delfino's treatise, pub-
lished in France the description of the tides given in
that work.
XV. Statics in the Sixteenth Century — Stevinus. — When writing on statics Cardano drew upon two sources, the writings of Archimedes and the treatises of the School of Jordanus; besides, he probably plagiarized the notes left by Vinci, and it was perhaps from this source that he took the theo- rem: a system endowed with weight is in equilibrium when the centre of gravity of this system is the lowest possible.
Nicole Tartaglia (about 1500-57), Cardano's an- tagonist, shamelessly purloined a supposedly for- gotten treatise by one of Jordanus's commentators. Ferrari, Cardano's faithful disciple, harshly rebuked Tartaglia for the theft, which nevertheless had the merit of re-establishing the vogue of certain discov- eries of the thiit(>enth century, especially the law of the eciuilibrium of a body supported by an inclined plane. By another and no less barefaced plagiarism, Tartaglia published under his own name a translation of Archimedes's "Treatise on floating bodies" made by William of Moerbeke at the end of the thirteenth century. This publication, dishonest though it was, helped to give prominence to the study of Arch- imedes's mechanical labours, which study exerted the greatest influence over the progress of science at the end of the sixteenth century, the blending of Archimedean mathematics with Parisian physics, generating the movement that terminated in Galileo's work. The translation and explanation of the works of Archimedes enlisted the attention of geometricians such as Francesco Maurolycus of Messina (1494- 1.575) and Federico Commandinoof Urbino (1509-75), and these two authors, continuing the work of the great Syracusan, determined the position of the centre of gravity of various solids; in addition Com- mandin translated and explained Pappus's mathe- matical "Collection", and the fragment of "Mechan- ics" by Heron of Alexandria appended thereto. Admiration for these monuments of ancient science inspired a number of Italians with a profound con- tempt for medieval statics. The fecundity of the prin- ciple of virtual displacements, so happily employed by the School of Jordanus, was ignored; and, de- prived of the laws discovered by this school and of the additions made to them by Vinci, the treatises on statics written by over-enthusiastic admirers of the Archimedean method were notably deficient. Among the authors of these treatises Guidobaldo dal Monte (1545-1607) and Giovanni Battista Benedetti (1530-90) deserve special mention.
Of the mathematicians who, in statics, claimed to follow exclusively the rigorous methods of Archimedes and the Cireek geometricians, the most illustrious was Simon Stevinus of Hrugcs ( 154S-1(;20). Through him the .statics (if .solid bodies recovered all that had been gained by the Si-liool of Jordanus and Vinci, and lost by the contempt of such men as Guidobaldo del Monte and Benedetti. The law of the equilibrium of the lever, one of the fundamental propositions of which Stevinus made use, was established by him with the aid of an ingenious demonstration which Galileo was also to employ, and which is found in a small anonymous work of the thirteenth century. In order to confirm another essential principle of his theory, the law of the equilibrium of a body on an inclined plane, Stevinus resorted to the impossibility of per- petual motion, which had been affirmed with great precision by Vinci and Cardano. Stevinus's chief
