Al-Sufi describes very clearly the four bright stars of the famous "Southern Cross." Owing to precession these stars were some 7° further north in the tenth century than they are at present, and they could have been all seen by Al-Sufi, when on the meridian. In the time of Ptolemy and Hipparchus, they were still further north, and about 5000 years ago they were visible in the latitude of London. Dante speaks of these four stars as emblematical of the four cardinal virtues, Justice, Temperance, Fortitude, and Prudence. Closely south-east of α and β Crucis is the dark spot in the Milky Way known as the "Coal Sack," which forms such a conspicuous object near the Southern Cross. It was first described by Pinzon in 1499; and afterwards by Lacaille in 1755. Although to the naked eye apparently black, photographs show that it contains many faint stars, but, of course, much less numerous than in the surrounding regions. The dark effect is chiefly caused by contrast with the brilliancy of the Milky Way surrounding it. Al-Sufi also mentions the bright stars α and β Centauri which follow the Southern Cross. He says that the distance between them "is four cubits," that is about 9° 20', but it is less than this now. α has a large "proper motion" of 3"·67 per annum, and was farther from β in Al-Sufi's time than it is at present. This, however, would not _wholly_ account for the difference, and Al-Sufi's over-estimate is probably due to the well-known effect by which the distance between two stars is _apparently_ increased when they are near the horizon. Several of Al-Sufi's distances between southern stars are over-estimated, probably for the same reason. The constellation Lupus, the Wolf, is south of Libra and Scorpio. It lies along the western border of the Milky Way. According to ancient writers it represents Lycaon, King of Arcadia, a contemporary of Cecrops, who is said to have sacrificed human victims, and on account of his cruelty was changed into a wolf. Another fable is that it represents a wolf sacrificed by the Centaur Chiron. According to Brown, Lupus appears on the Euphratian planisphere discovered by George Smyth in the palace of Sennacherib. Al-Sufi called it _al-sabu_, "the Wild Beast." It was also called _al-fand_, "the Leopard," and _al-asada_, "the Lioness." Ara, the Altar, lies south of Scorpio. According to ancient writers it represents an altar built by Vulcan, when the gods made war against the Titans. It is called by Al-Sufi _al-midjman_, "the Scent Box," or "the Altar." The little constellation Corona Australis, the Southern Crown, lies south and west of Sagittarius, east of Scorpio, and west of Telescopium. Aratus refers to the stars in Corona Australis as-- "Other few Before the Archer under his forefeet Led round in circle roll without a name."[449]