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

16 ASTRONOMY IN ANCIENT NATIONS equal to 57, the second one equal to 56¼ Arabian miles of 4000 black cubits, and the approximate mean, 56⅔ miles, was adopted as the final result, the circumference of the Earth being 20,400 miles and the diameter 6500 miles. Another report, by Ahmed ben Abdallah, called Habash, an astronomer under Al Mamun (quoted by Ibn Jūnis), states that a party of observers (no names given) proceeded along the plain of Sinjar until they found a difference in meridian altitudes, measured the same day, equal to one degree, while the distance travelled over was found to be 56¼ miles¹. Probably two different determinations were made. If the "black cubit" is the Egyptian and Babylonian cubit of 525 mm.², the mile would be=2100 m. and 56⅔ miles=119,000 meters, rather a large result. The doctrine of the spherical earth remained undisputed in the Muhammedan learned world, though the curious error of assuming that the level of the sea was higher on some parts of the Earth than on others appears to have found some adherents among Arabian writers as well as in Europe.³ We may, there- fore, at once pass on to the motions of the heavenly bodies. Al Battani determined the longitude of the Sun's apogee and found it=82° or 16° 47¹ more than Ptolemy had given. As he believed

1. Caussin, Not. et Extraits. vii. pp. 94-96 ; Delambre, Hist. de l'astr du Moyen Age. pp. 78 and 97; Shems ed-din, Manuel de la cosmographie, traduit par Mehren, Copenhague. 1874 p. 6. Suter, p. 209, mentions a third report (from Ibn Challikān's Biographical Dictionary), according to which the sons of Musa first measured in the plain of Sinjar and afterwards as a test at Kufa, by order of Al Mamun. The eldest of the sons of Musa died 41 years after Al Mamun, and the names of the observers in the first report are different, so that the third report is not to be relied on. Al Fargani merely gives 56⅔ miles as the result of Al Mamun. According to Shah Cholgii Astronomica . . . . studio et opera Ioh. Gravii, Lon- don, 1652, p. 95, Ala ed-din Al Kusgi (one of the Ulug Begh's astronomers) gives the circumference of the earth=8000 parasangs. As a persian parasang =30 stadia (Hultsch; Griech u. Rom. Metrologie. p. 476) this would seem to be the value of Posidonius, 240,000 stadia. Kazwini (p. 298) gives the circu- mference=6800 parasangs on the authority of Al Beruni.
2. Hultsch p- 390.
3. It deserves to be mentioned that Shems ed-din of Damascus (1256-1327) explains the great Preponderance of dry land in the northern hemisphere by the attraction of the Sun on the water, which is the greatest when the Sun is in perigee, at which time it is nearly at its greatest south declination. That this accumulation of water would not be a permanent one does not occur to him (Cosmographie, p. 4).