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LEFT ASTRONOMY 317 ASTRONOMY course of 24 hours. The work by which he is best known, however, is the col- lection and systematic arrangement of the ancient observations in his great work, the "Megale Syntaxis," which gives a complete resume of the astro- nomical knowledge of the day. The most important part of it is the seventh and eighth books, which contain the catalogue of stars which bears Ptolemy's name, though it is only a compilation of the catalogue of Hipparchus with the positions brought up to the time of Ptol- moon's motion, the variation, and de- termined its amount. The revival of astronomy in Europe may be said to have begun with George Purbach, who translated the "Alma- gest" at Vienna. His pupil, John Mul- ler, translated into Latin the works of Ptolemy and the conies of Appolonius, built an observatory at Nuremberg, and equipped it with instruments of his own invention. He died in 1476. Copernicus (1473-1543) exploded the Ptolemaic idea, and promulgated a cor- ^ CMVAS < DOME PI?OT£CriPN THE DOME AND MOUNTING FOR A 60" REFLECTING TELESCOPE emy. These latter are in use to-day, though the gaps between them have been filled up in some cases by more modern asterisms. To the Arabs we owe the next ad- vances in astronomy. The most illus- trious of the Arabian school were Alba- tegnus, or AI Batani (880 A. D.), who dis- covered the motion of the solar apogee, and who was the first to make use of sines and versed sines instead of chords; and Ibn-Yunis (1000 A. D.), an excellent mathematician, who made observations of great importance in determining the disturbances and eccentricities of Jupi- ter and Saturn, and who was the first to use cotangents and sectants. Like- wise, at about the same time, Abul Wefa discovered the third inequality in the rect theory. It makes the sun the im- movable center of the universe, around which all the planets revolve in concen- tric orbits, Mercury and Venus within the earth's orbit, and all other planets without it. Decidedly the most industrious ob- server and eminent practical astronomer from the time of the Arabs to the latter half of the 16th century was Tycho Brahe (1546-1601). He made the first table of refractions, and discovered the variation and annual equation of the moon, the inequalities of the motion of the nodes, and of the inclination of the lunar orbit. He also demonstrated that the region of the comets is far beyond the orbit of the moon, and he deter- mined the positions of 777 stars with