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 PHYSICS

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PHYSICS

those with which the Earth was provided, and he maintained that the moon moved in a circle around the Earth.

Of the Copernican hjTJothescs, the newest was that according to which the Earth moved in a circle around the sun. From the days of Aristarchus of Samos and Seleucus no one had adopted this view. Me- dieval astronomers had all rejected it, because they supposed that the stars were much too close to the Earth and the sun, and that an annual circular motion of the Earth might give the stars a perceptible parallax. Still, on the other hand, we have seen that various authors had proposed to attribute to the Earth one or the other of the two motions which Copernicus added to the annual motion. To defend the hj'pothesis of the daily motion of the Earth against the objections formulated by Peripatetic physics, Copernicus invoked exactly the same reasons as Oresme, and in order to explain how each planet retains the various parts of its elements, he adopted the theorj- of gravity proposed by the eminent mas- ter. Copernicus showed himself the adherent of Parisian physics even in the following opinion, enun- ciated accidently: the acceleration of the fall of hea\-j' bodies is ex-plained by the continual increase which impetus receives from gra\-ity.

XIII. Fortunes of the Copernican System in THE Sixteenth Centl'rv. — Copernicus and his disciple Rh^ticus verj- probably regarded the motions which their theory ascribed to the Earth and the planets, the sun's rest and that of the firmament of fixed stars, as the real motions or real rest of these bodies. The "De revolutionibus orbium ca;lestium libri sex" appeared with an anonymous preface which inspired an entirely different idea. This pref- ace was the work of the Lutheran theologian Osian- der (1498-1552), who therein expressed the opinion that the hj-potheses proposed by pliilosophers in general, and by Copernicus in particular, were in no wise calculated to acquaint us with the reality of things: "Neque enim necesse est eas hypotheses esse veras, imo, ne verisimiles quidem, sed sufficit hoc unum si calculum observationibus eongruentem exhibeant". Osiander's view of astronomical hy- potheses was not new. Even in the days of Grecian antiquity a number of thinkers had maintained that the sole object of these hypotheses was to ''save appearances", ffiiffii' rd (paivdfKva; and in the Middle Ages, as well as in antiquity, this method continued to be that of philosophers who wished to make use of Ptolemaic astronomy whilst at the same time up- holding the Peripatetic physics absolutely incom- patible ^ith this astronomy. Osiander's doctrine was therefore readily received, first of all by astron- omers who, without beheving the Earth's motion to be a reaUty, accepted and admired the kinetic combinations conceived by Copernicus, as these combinations provitled them with better means than could be offered bj' the Ptolemaic system for figuring out the motion of the moon and the phenomena of the precession of the equinoxes.

One of the astronomers who most distinctly as- sumed this attitude in regard to Ptolemy's system was Erasmus Reinhold (1511-5.3), who, although not admitting the Earth's motion, professed a great admiration for the system of Copernicus and used it in computing new astronomical tables, the " Prutenicse tabuls" (1551), which were largely instrumental in introducing to astronomers the kinetic combinations originated by Copernicus. The "Prutenica; tabula>" were especially employed bj- the commission which in 1582 effected the Gregorian reform of the calendar. Whilst not believing in the Earth's motion, the mem- bers of this commission did not hesitate to use tables founded on a theory of the precession of the equi- noxes and attributing a certain motion to the earth.

However, the freedom permitting astronomers to

use all hypotheses qualified to account for phenomena was soon restricted by the exigencies of Peripatetic philosophers and Protestant theologians. Osiander had written his celebrated preface to Copernicus's book with a view to warding off the attacks of theo- logians, but in this he did not succeed. ^lartin Luther, in his "Tischrede", was the first to express indignation at the impiety of those who admitted the hypothesis of solar rest. Melanchthon, although acknowledging the purely astronomical ativantages of the Copernican system, strongly combatted the hj-pothesis of the Earth's motion (1549), not only with the aid of arguments furnished by Peripatetic physics but likewise, and chiefly, with the assistance of numerous texts taken from Holy ^^"rit. Kaspar Peucer (1525-1602), Melanchthon's son-in-law, whilst endeavouring to have his theorj' of the planets har- monize with the progress which the Copernican sj'stem had made in this regard, nevertheless rejected the Copernican hypotheses as absurd (1571).

It then came to be exacted of astronomical hj-poth- eses that not only, as Osiander had desired, the result of their calculations be conformable to facts, but also that they be not refuted "either in the name of the principles of physics or in the name of the authority of the Sacred Scriptures". This criterion was expUc- itly formulated in 1578 by a Lutheran, the Danish astronomer Tycho Brahe (1546-1601), and it was precisely by virtue of these two requirements that the doctrines of Galileo were to be condemned by the Inquisition in 1616 and 1633. Eager not to admit any hypothesis that would conflict with Aristotelean physics or be contrarj- to the letter of the Sacred Scriptures, and yet most desirous to retain all the astronomical advantages of the Copernican sj-stem, Tycho Brahe proposed a new system which virtually consisted in leaving the Earth motionless and in moving the other heavenly bodies in such a waj- that their displacement with regard to the Earth might remain the same as in the sj'stcm of Copernicus. Moreover, although posing as the defender of Aris- totelean physics, Tycho Brahe dealt it a disastrous blow. In 1572 a star, until then unknown, appeared in the constellation of Cassiopeia, and in showing accurate observations that the new astral body was really a fixed star, Tycho Brahe proved conclusively that the celestial world was not, as Aristotle would have had us believe, formed of a substance exempt from generation and destruction.

The Church had not remained indifferent to the hj-pothesis of the Earth's motion until the time of Tycho Brahe, as it was amongst her members that this hj'pothesis had found its first defenders, counting adherents even in the extremely orthodox University of Paris. At the time of defencUng this hypothesis, Oresme was Canon of Rouen, and immediately after he was promoted to the Bishopric of Lisieux; Nicholas of Cusa was Bishop of Brixen and cardinal, and was entrusted with important negotiations by Eugenius IV, Nicholas V, and Pius II; Calcagnini was protho- notary Apostolic; Copernicus was Canon of Thorn, and it was Cardinal Schomberg who urged him to publish his work, the dedication of which was ac- cepted by Paul III. Besides, Oresme had made clear how to interpret the Scriptural passages claimed to be opposed to the Copernican system, and in 1584 Didacus a Stunica of Salamanca found in Holy Writ texts which could be invoked with just as much certainty in favour of the Earth's motion. However, in 1595 the Protestant senate of the University of Tiibingen compelled Kepler to retract the chapter in his "Mysterium cosraographicum ", in which he had endeavoured to make the Copernican system agree with Scripture.

Christopher Clavius (1537-1612), a Jesuit, and one of the influential members of the commission that reformed the Gregorian Calendar, seemed to be the