222 COSMOS. 



periodic course of the magnetic needle, and in the distribution 

 of organisms over the earth's surface. 



The Arabs were in possession of planetary tables* as early 

 as the close of the eighth century. We have already observed 

 that the Sus7'uta, the ancient incorporation of all the medical 

 knowledge of the Indians, was translated by learned men be- 

 longing to the court of the Calif Haroun Al-Raschid — a proof 

 of the early introduction of Sanscrit literature. The Arabian 

 mathematician Albiruni even went to India for the purpose 

 of studying astronomy. His writings, which have only recent- 

 ly been made accessible to us, prove how intimately he had 

 made himself acquainted with the country, traditions, and 

 comprehensive knowledge of the Indians. t 



However much the Arabian astronomers may have owed to 

 the earlier civilized nations, and especially to the Indian and 

 Alexandrian schools, they have, nevertheless, considerably ex- 

 tended the domain of astronomy by their own practical en- 

 dowments of mind ; by the number and direction of their ob- 

 servations ; the improvement of their instruments for angular 

 measurement ; and their zealous efforts to rectify the older ta- 

 bles by a comparison with the heavens. In the seventh book 

 of the Almagest of Abul-Wefa, Sedillot found a notice of the 

 important inequality in the moon's longitude, which disappears 

 at the syzygies and quadratures, attains its maximum at the 

 octants, and has long been regarded, under the name oi varia- 

 tion, as the discovery of Tycho Brahe.J The observations of 



* On the Indian tables which Alphazari and Alkoresmi translated 

 into Arabic, see Chasles, Recherches sur V Astronomie Indienne, in the 

 Compies Rendus des Stances de VAcad. des Sciences, t. xxiii., 1846, p. 

 846-850. The substitution of the sine for the arc, which is usually 

 ascribed to Albategnius, in the beginning of the tenth century, also 

 belongs originally to the Indians; tables of sines are to be found in the 

 Surya-Siddhanta. 



t Reinaud, Fragments Arales relatifs a Vlnde, p. xii.-xvii., 96-126, 

 and especially 135-160. Albiruni's proper name was Abul-Ryhan. 

 He was a native of Byrun, in the Valley of the Indus, and a friend of 

 Avicenua, with whom he lived at the Arabian academy which had 

 been formed in Charezm. His stay in India, and the composition of 

 his history of that country ( TaHkhi-Hind), of which Reinaud has made 

 known the most remarkable fragments, belong to the years 1030-1032. 



X Sedillot, MaUriaitx pour servir a V Histoire comparie des Sciences 

 Mathematiques chez les Grecs et les Orientattx, t. i., p. 50-89 ; also in 

 the Comptes Rendus de VAcad. des Sciences, t. ii., 1836, p. 202; t. xvii., 

 1843, p. 163-173 ; t. xx., 1845, p. 1308. In opposition to this opinion, 

 Biot maintains that the fine discovery of Tycho Brahe by no means 

 belongs to Abul-Wefa, and that the latter was acquainted, not with the 

 " variation," but only with the second part of the ** evection." {Journal 



