ब्राह्मस्फुटसिद्धान्त (ब्रह्मगुप्त - शून्य, कुट्टक, बीजगणित एवं सम्पूर्ण २१ अध्याय सान्वय सटीक)

ARABS ON MOTIONS OF FIXED STARS 43 nomenon; among them are Al Sūfi, the author of the only urano- metry of the Middle Ages³, who followed Al Battani, also Abu 'l Faraj and Jagmini,¹ while Nasir ed-din mentions it but seems to doubt its reality.² By others it was willingly accepted, for instance by Al Zarkali, who made the period of oscillation of 10° either way equal to 2000 Muhammedan years (or 1940 Gregorian years, i.e. 1° in 97 years or 37" a year). The motion is in a circle of 10° radius; at the Hijra the movable equinox was it 40' in increasing precession, and in A: D. 1080 at 7° 25'.³. The diminu- tion of the inclination of the ecliptic, which the astronomers of Al Mamun had found=23° 33', no doubt lent countenance to the idea of trepidation, and the next step in the development of this curious theory was the combination of progressive and oscillatory motion. Al Betrugi, who gives a sort of history of the theory, beginning with a mythical H mes, makes out that Theon (or Taun Alexandrinus as he calls him) com- bined the motion of 1° in 100 years with the oscillation³. A century later this was actually done, and the theory received its last development by King Alfonso or his astronomers, who⁴ perceived that the equinoxes had receded much further than Tabit's theory allowed. The equioxes were now supposed to pass right round the heavens in 49,000 years (annual motion=26".45), while the period of the inequality of trepidation was 7000 years, so that in a sort of Great Jubilee year everything was again as it had been in the beginning.⁵ The progressive motion belongs to

1. Abu 'l Faraj, p. 12, simply says that the motion is 1° in 100 years according to Ptolemy, or 1° in 66 years according to others. But on p. 18 he says that if the ancient Chaldeans gave the tropical points a motion backwards and . and forwards, and if ancient astrologers adopted this, then the motion of the fixed stars must have been unknown to them. Jagmini (p. 229) says that most people adopt 1° in 66 solar years.
2. Spheres celestes, p. 347.
3. Sedillot, Memoire sur les instr. astr. des Arabes, pp. 31, 32. Abraham ben Chija (p. 196 of Munster's Sphaera mundi. Basle, 1546) gives the period as 1600 years without quoting any authority. He adds that the ancient Indians. Egyptians, Chaldeans, Greeks, and Latins first proposed the theory—Ptolemy neither approved nor disapproved of it, but Al Battani confuted it.
4. Alpetragius, f. 12a. He says that Al Zarkali did the same.
5. A later writer, Augustinus Ricius. De motu octave sphaere, Paris, 1521, who traces the theory back to Hermes, 1985 years before Ptolemy (!) credits (Continued on next page)