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 PHYSICS

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PHYSICS

tament (Matt., xxiii, 5), in the great discourse of Our Lord against the Pharisees whom He reproaches with ostentation in the discharge of their rehgious and social duties: "For they make their phylacteries broad and enlarge their fringes". By the Jews the phylacteries are termed lephillin, plural of the word tephillah, "a prayer", and consist of two small square

Arm entwined with Phylactery

cases of leather, one of which is worn on the forehead, the other on the upper left arm. The case for the forehead holds four distinct compartments, that for the arm only one. They contain narrow strips of parchment on which are copied passages from the Pentateuch, viz., Ex., xiii, 1-10; and Deut., vi, 4-9; xi, 13-21. The practice of wearing the phylacteries at stated moments is still regarded as a sacred reli- gious duty by the orthodox Jews.

Klein. Die Totaphoth nach Bibel und Tradition in Jahrbiicker f. Prot. Theol. (Berlin. 1881), 666-689; Viqodrodx, Did. de la Bible, 3. V. Phylacth-es.

James F. Driscoll.

Physics, History of. — The subject will be treated under the following heads: — I. A Glance at Ancient Physics; II. Science and Early Christian Scholars; III. A Glance at Arabian Physics; IV. Arabian Tradi- tion and Latin Schola-sticism; V. The Science of Ob- servation and Its Progress — Astronomers — The Stat- ics of Jordanus — Thierry of Freiberg — Pierre of Maricourt; VI. The Articles of Paris (1277) — Possi- bility of Vacuum; VII. The Earth's Motion — Oresme; VIII. Plurality of Worlds; IX. Dynamics — Theory of Impetus — Inertia — Celestial and Sublunary Mechan- ics Identical; X. Propagation of the Doctrines of the School of Paris in Germany and Italy — Purbach and Regiomontanus — Nichohis of Cusa — Vinci; XI. Ital- ian Averroism and its Tendencies to Routine — At- tempts at Restoring the Astronomy of Homocentric Spheres; XII. The Copernican Revolution; XIII. Fortunes of the Copernican System in the Sixteenth Century; XIV. Theory of the Tides; XV. Statics in the Sixteenth Century — Stevinus; XVI. Dynamics in the Sixteenth Century; XVII. Galileo's Work; XVIII. Initial Attempts in Celestial Mechanics — Gilbert — Kepler; XlX. Controversies concerning Geostatics; XX. Descartes's Work; XXI. Progress of Experimental Physics; XXII. Undulatory Theory of Light; XXIII. Development of Dynamics; XXIV. Newton's Work; XXV. Progress of General and Celes- tial Mechanics in the Eighteenth Century; XXVI. Establishment of the Theory of Electricity and Mag- netism; XXVII. Molecular Attraction; XXVIII. Revival of the Undulatory Theory of Light; XXIX. Theories of Heat.

I. A Glance at Ancient Physics. — Although at the time of Christ's birth Hellenic science had pro- duced nearly all its masterpieces, it was still to give to the world Ptolemy's astronomy, the way for which had been paved for more than a century by the works of Hipparchus. The revelations of Greek thought on the nature of the exterior world ended with the "Almagest", which appeared about a. d. 14.5, and then began the decline of ancient learning. Those of its works that escaped the fires kindled by Moham- medan warriors were subjected to the barren inter- pretations of Mussulman commentators and, like parched seed, awaited the time when Latin Chris- tianity would furnish a favourable soil in which they could once more flourish and bring forth fruit. Hence jt is that the time when Ptolemy put the finishing

touches to his "Great Mathematical Syntax of Astron- omy" seems the most opportune in which to study the field of ancient physics. An impassable frontier separated this field into two regions in which different laws prevailed. From the moon's orbit to the sphere enclosing the world, extended the region of beings exempt from generation, change, and death, of per- fect, divine beings, and these were the star-sphere and the stars themselves. Inside the lunar orbit lay the region of generation and corruption, where the four elements and the mixed bodies generated by their mutual combinations were subject to perpetual change.

The science of the stars was dominated by a prin- ciple formulated by Plato and the Pythagoreans, according to which all the phenomena presented to us by the heavenly bodies must be accounted for by combinations of circular and uniform motions. More- over, Plato declared that these circular motions were reducible to the rotation of solid globes all limited by spherical surfaces concentric with the World and the Earth, and some of these homocentric spheres carried fixed or wandering stars. Eudoxus of Cnidus, Cal- ippus, and Aristotle vied with one another in striving to advance this theory of homocentric spheres, its fundamental hypothesis being incorporated in Aris- totle's "Physics" and "Metaphysics". However, the astronomy of homocentric spheres could not explain all celestial phenomena, a considerable number of which showed that the wandering stars did not always remain at an equal distance from the Earth. Hera- clides Ponticus in Plato's time, and Aristarchus of Samos about 280 B. c. endeavoured to account for all astronomical phenomena by a heliocentric system, which was an outline of the Copernican mechanics; but the arguments of physics and the precepts of theology proclaiming the Earth's immobility, readily obtained the ascendency over this doctrine which existed in a mere outline. Then the labours of Apol- lonius Perga^us (at Alexandria, 205 b. c), of Hip- parchus (who made observation at Rhodes in 128 and 127 B. c), and finally of Ptolemy (Claudius Ptol- ema;us of Pelusium) constituted a new astronomical system that claimed the Earth to be immovable in the centre of the universe; a system that seemed, as it were, to reach its completion when, between A. D. 142 and 146, Ptolemy wrote a work called "Me7d\7; fiuO-rjiuLTiKr] auvTa^ii Tri% atrrpovoiilas", its Arabian title being transliterated by the Christians of the Middle Ages, who named it "Almagest". The astronomy of the "Almagest" explained all astronomical phe- nomena with a precision which for a long time seemed satisfactory, accounting for them by combinations of circular motions; but, of the circles described, some were eccentric to the World, whilst others were epi- cyclic circles, the centres of which described deferent circles concentric with or eccentric to the World; moreover, the motion on the deferent was no longer uniform, seeming so only when viewed from the centre of the equant. Briefly, in order to construct a kine- matical arrangement by means of which phenomena could be accurately represented, the astronomers whose work Ptolemy completed had to set at naught the properties ascribed to the celestial substance by Aristotle's "Physics", and between this "Physics" and the astronomy of eccentrics and epicycles there ensued a violent struggle which lasted until the middle of the sixteenth century.

In Ptolemy's time the physics of celestial motion was far more advanced than the physics of sublunary bodies, as, in this science of beings subject to genera- tion and corruption, only two chapters had reached any degree of perfection, namely, those on optics (called perspective) and statics. The law of reflec- tion was known as early as the time of Euclid, about 320 B. c, and to this geometrician was attributed, al- though probably erroneously, a "Treatise on Mir-