We saw in Chapter I that two theories prevailed in ancient times as to the distribution of land and water: the oceanic theory, that the _oikoumene_ is surrounded by water; and the continental theory, that the oceans of the earth occupy relatively small and enclosed basins. Though the writers of our period held to the oceanic hypothesis, they had various and conflicting notions in regard to the size of the ocean or oceans which surround the known world. The great popularity of Martianus Capella and Macrobius, who both held the doctrine that there are three areas of land corresponding to our _oikoumene_ in the three quarters of the earth’s surface, must have rendered impossible any widespread acceptance of a theory like the one hinted at by Abelard, that all of the earth’s surface except the _oikoumene_ is covered by water; and the definition of the ocean as a zone or hem surrounding the inhabited world, not infrequently given in our period, certainly does not imply the existence of water areas of immense size in comparison with the land areas.[847] Furthermore, the Second Book of Esdras, which, though apocryphal, enjoyed high authority in the Middle Ages,[848] gave the reader an opposite impression. Here it was stated: “Upon the third day thou didst command that the waters should be gathered in the seventh part of the earth: six parts hast thou dried up, and kept them, to the intent that of these some being planted of God and tilled might serve thee.” “Upon the fifth day thou saidst unto the seventh part, where the waters gathered, that it should bring forth living creatures, fowls and fishes: and so it came to pass.” Roger Bacon uses this text from Esdras to reinforce his argument that, relatively speaking, the water surface of the world is very restricted in comparison with the land surface.[849] EXPLANATION OF UNIFORM LEVEL OF SEA SURFACE Into the sea there pours at all times a vast volume of water from the rivers. Neckam moralized mournfully on this[850] and compared the flow of fresh water into the salt depths with the way in which greater powers absorb lesser and the way in which the voluptuousness of this world—a sham sweetness—is turned to bitterness and salt; but he did not attempt to explain the puzzling physical problem of why the surface of the sea fails to rise and overflow the lands.[851] Most writers who dealt with the latter problem appealed to the theory of the _congregatio aquae_: since all the waters of the earth form one unit, they must inevitably make their way back from the sea through various routes to the sources of streams.[852] Other explanations, however, were sometimes brought forward. Adelard of Bath believed that the stars and sun absorb a certain amount of water.[853] The author of the _De imagine mundi_ was convinced that the fresh water entering the sea is partially consumed by the salt of the deeps and partially evaporated by the winds and taken up into the sun.[854]