The earth's disc, the _orbis terrarum_, was covered according to Homer by a solid vault or firmament, beneath which the stars of the day and night were carried by chariots supported by the clouds. In the morning the sun rose from the eastern ocean, and in the evening it declined into the western; and a vessel of gold, the mysterious work of Vulcan, carried it quickly back by the north, to the east again. Beneath the earth Homer places, not the habitation of the dead, the caverns of Hades, but a vault called Tartarus, corresponding to the firmament. Here lived the Titans, the enemies of the gods, and no breath of wind, no ray of light, ever penetrated to this subterranean world. Writers subsequent to Homer by a century determined even the height of the firmament and the depth of Tartarus. An anvil, they said, would take nine days to fall from heaven to earth, and as many more to fall from earth to the bottom of Tartarus. This estimate of the height of heaven was of course far too small. If a body were to fall for nine days and nights, or 777,600 seconds under the attraction of the earth, it would only pass over 430,500 miles, that is not much more than half as far again as the moon. A ray of light would only take two seconds to pass over that distance, whereas it takes eight minutes to reach us from the sun, and four hours to come from Neptune--to say nothing of the distance of the stars. The limits of the world in the Homeric cosmography were surrounded by obscurity. The columns of which Atlas was the guardian were supported on unknown foundations, and disappeared in the systems subsequent to Homer. Beyond the mysterious boundary where the earth ended and the heavens began an indefinite chaos spread out--a confused medley of life and inanity, a gulf where all the elements of heaven, Tartarus, and earth and sea are mixed together, a gulf of which the gods themselves are afraid. Ideas such as these prevailed long after geometers and astronomers had proved the spherical form of the globe, and they were revived by the early Christian geographers and have left their trace even on the common language of to-day. [Illustration: FIG. 32.--HOMERIC COSMOGRAPHY.] The centre of the terrestrial disc was occupied by the continent and isles of Greece, which in the time of Homer possessed no general name. The centre of Greece passed therefore for the centre of the whole world; and in Homer's system it was reckoned to be Olympus in Thessaly, but the priests of the celebrated Temple of Apollo at Delphi (known then under the name of Python) gave out a tradition that that sacred place was the real centre of the habitable world.