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

20 ASTRONOMY IN ANCIENT NATIONS facts, as Biot has shown from the Ptolemy's numerical data that the deviation of the line of apsides reaches its maximum value of ± 13° 8′ .9 in elongations 90° ∓ 32° 57′.5.¹ But it must be acknowledged that the words in question are also used very vaguely, e. g. by Abu 'l Wefa himself, who says that the velocity of the superior planets after emerging from the Sun's rays dimi- nishes gradually till their distance from the Sun is about a tathlith, when they become stationary. It looks almost as if these words might be used to denote any elongation outside syzygy and quadrature.² If Abu 'l Wefa had made a new discovery, we should have expected later Arabian astronomers to have alluded to it. But not one of them gives anything but interpretations of the lunar theory of Ptolemy, and in expressions very similar to those employed by Abu 'l Wefa. Attention was at once called to this fact, and Isaac Israeli of Toledo (about 1310) and Geber of Seville were quoted as examples,³ though it would, of course, have been quite possible for these two writers to have remained ignorant of whatever progress astronomy might have made in the school of Baghdad. But this objection does not apply to Nasir ed-din al Tusi, in whose review of the Almagest and Mem- orial of Astronomy the inequalities known to Ptolemy and no others, are described and credited to Ptolemy⁴; not to Mahamud al Jagmini (about 1300) , who wrote a compendium (mulachchas)

1. Journal des Savants, 1843, p. 701 ("Sur un traite arabe relatif a l' astro- nomie," Reprint, p. 47). This deviation does not represent the amount of the correction to the Moon's place as seen from the Earth, so that there is not any contradiction in Ptolemy's account.
2. Carra de Vaux, l. c. p. 466. The Arabs had no word for "octants." Nasir- ed-din on one occasion wants to mention them, and has to call them "the points midway between syzygy and quadrature." 3 Isaac Israeli repeatedly speaks of these inequalities discovered by Ptolemy, two of which are not found at conjunction and opposition. Liber Jesod, Olam seu Fundamentum Mundi auctore R. Isaac Israeli Hispano, section III. ch. 8 and sect. v. ch. 16, Part I. p. xxiv Part II. p. xxxi (Berlin, 1848 and 1846 ; this publication is not mentioned by Carra de Vaux).
3. C. de Vaux, "Les spheres celestes selon Nasir Eddin Attusi", Appendix to P. Tannery's Recherches sur l' astr. anc. p. 342, and Journ. asiat. 1892, p. 459 : "The third anomaly is that of the prosneusis ; it is called the equation of the proper motion" (i.e. of the motion on the epicycle).