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

NASIR ED-DIN AL TŪSI 37 was apparently not ripe for a radical change with regard to this idea. Though the doctrine of the Earth's motion does not seem to have been mentioned by Arabian writers, we have evidence - that the hypothesis of the daily rotation of the Earth was not unknown among them, a natural consequence of their familiarity with the writers of antiquity. One of Nasir ed-din's fellow-workers at the Meragha observatory, Ali Negm ed-din al Katibi, who died in 1277, wrote a book, the Hikmat al-ain, on philosophy, in which he combats this opinion, which he attritutes to "some philos- phers." "I do not," he says, "advance as an argument against it that, if this were the case, a bird flying in the direction of the motion of the Earth would not be able to keep up with it, because the motion of the Earth would be much faster than that of a bird, inasmuch as it returns to its place in a day and a night. Such an argument is not conclusive, because it may be urged that the atmosphere which is close to the Earth partakes of its motion as the ether partakes of the motion of the heavenly sphere. But I reject this theory, because all terrestrial motions take place in a straight line, and therefore we cannot admit that the Earth should move in a circle."¹ What reformation of astronomy could be hoped for, as long as this kind of argument could be used ? We cannot see from this remark of Katibi's whether there really were any Arabian philosophers who believed in the rotation of the Earth. It is, however, stated in the Zohar, the great Kabbalistic work attribu- ted to Mosheh ben Shemtob of Leon (died 1305), that a certain Rabbi Hamnuna the Elder (otherwise unknown) taught that "the Earth turns like a sphere in a circle and that some people are above and others below."² Though this passage as well as others in the Zohar may have been interpolated much later, it would

1. A. Sprenger, "The Copernican System of Astronomy among the Arabs." Journ. Asiat. Society of Bengal, Vol. XXV. (1857), p. 189. Katibi's con- temporary, Abu 'l Faraj (II. p. 10) deems it necessary to prove that the Earth cannot be in motion, neither rectilinear nor circular, but his argu- ments (about birds and stones flung upwards) seem merely taken from Ptolemy, lib, 1. cap. 6. Kazwini (Kosmographie, p. 296) says that among the ancients there were some adherents of Pythagoras who maintained that the Earth continually moves round in a circle ; but whether these adherents were Greeks or Arabians cannot be seen from the context.
2. Sohar, Amsterdam, 1718, T. III. f. 10a ; Gunther, Studien Z. Gesch. d. math, Geogr., p. 113.