In the fifth century before Christ, Herodotus, the most celebrated traveller of antiquity, and consequently capable of forming rational ideas upon the subject of geography, rectified many errors which had crept into the popular belief, though Homer was still considered infallible by the masses of the people. "I know of no such river as the ocean," he says, ironically: "this denomination seems to be a pure invention of Homer and the old poets. I cannot help laughing when I hear of the river Ocean, and of the spherical form of the earth, as if it were the work of a turner." He displaced the centre of the inhabited surface, which the Greeks had at first made Mount Olympus and afterwards Delphi, making Rhodes the fortunate possessor of the privilege. Socrates, a century later, (400 B.C.,) asserted that the earth was in the form of a globe, sustained in the middle of the heavens by its own equilibrium. About the year 230 B.C., Eratosthenes, a Greek of Cyrene, succeeded in reducing geography to a system, under the patronage of the Ptolemies of Egypt, which gave him access to the immense mass of materials gathered by Alexander and his successors and accumulated at the Alexandrian Library. The spherical form of the earth was now quite generally considered by scientific men to be the correct theory, though it could never be substantiated till some navigator, sailing to the east, should return by the west. Eratosthenes, proceeding upon this principle, made it his study to adjust to it all the known features of the globe. The great ocean of Homer and Herodotus, surrounding the world, still remained in his system. He compared, however, the magnitude of the regions known in his time with what he conceived to be the whole circumference, and became convinced that only a third part of the space was filled up. He conjectured that the remaining space might consist of one great ocean, which he called the Atlantic, from Mount Atlas, which was fancifully believed to support the globe. He supposed, too, that lands and islands might be discovered in it by sailing towards the west. We shall now proceed to give such a description of the vessels used by the Greeks after the time of Homer, as the confused and incomplete data which have reached us will enable us to furnish. [Illustration: THE GREAT PENGUIN.] [Illustration: A GREEK VESSEL OF THE SIXTH CENTURY B.C.] CHAPTER VI. CONSTRUCTION OF GREEK VESSELS--THE PROW, POOP, RUDDER, OARS, MASTS, SAILS, CORDAGE, BULWARKS, ANCHORS--BIREMES, TRIREMES, QUADRIREMES, QUINQUEREMES--THE GRAND GALLEY OF PTOLEMY PHILOPATOR--ROMAN VESSELS--THEIR NAVY--MIMIC SEA-FIGHTS--THE FIVE VOYAGES OF ANTIQUITY.