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).