There were several heroes of the name of Hercules, but the most famous was Hercules the Theban, son of Jupiter and Alcmene wife of Amphitryon, King of Thebes, who is said to have lived some years before the siege of Troy, and went on the voyage of the Argonauts about 1300 B.C. According to some ancient writers, another Hercules lived about 2400 B.C., and was a contemporary of Atlas and Theseus. But according to Pétau, Atlas lived about 1638 B.C., and Lalande thought that this chronology is the more probable. The small constellation Lyra, which contains the bright star Vega, is called by Al-Sufi the Lyre, the Goose, the Persian harp, and the Tortoise. In his translation of Al-Sufi's work, Schjellerup suggests that the name "Goose" may perhaps mean a plucked goose, which somewhat resembles a Greek lyre, and also a tortoise. The name of the bright star Vega is a corruption of the Arabic _vâki_. Ptolemy and Al-Sufi included all the very brightest stars in the "first magnitude," making no distinction between them, but it is evident at a glance that several of them, such as Arcturus and Vega, are brighter than an average star of the first magnitude, like Aldebaran. The constellation Perseus, which lies south-east of "Cassiopeia's Chair," may be recognized by the festoon formed by some of its stars, the bright star α Persei being among them. It is called by Al-Sufi "_barschânsch_, Περσευς, Perseus, who is _hamil râs al-gul_, the Bearer of the head of _al-gul_." According to Kazimirski, "_Gul_ was a kind of demon or ogre who bewilders travellers and devours them, beginning at the feet. In general any mischievous demon capable of taking all sorts of forms." In the Greek mythology Perseus was supposed to be the son of Jupiter and Danæ. He is said to have been cast into the sea with his mother and saved by King Polydectus. He afterwards cut off the head of Medusa, one of the Gorgons, while she slept, and armed with this he delivered Andromeda from the sea-monster.