Geography

​And in another way also he indicates that the ocean surrounds the earth in a circle, when he represents Hera as saying: “For I am going to see the limits of the fertile earth, and Oceanus, the origin of the gods.” For he says that the ocean is adjacent to all the “limits,” and the limits lie around in a circle. Also, in the making of the armor of Achilles, he places the ocean in a circle on the rim of the shield. It also belongs to the same scientific interest that he is not ignorant of the phenomena of the tides of the ocean, both the ebb and flow, calling it “backward-flowing Oceanus,” and also saying: “For three times in a day she sends it up, and three times she gulps it down.” For even if it is not three times but twice (perhaps because the historical fact was lost or the text was corrupted), yet his intention at least is of this kind. And the phrase “from the gently-flowing” also contains some indication of the tide, since it has a gentle onset and is not completely torrential. Posidonius says that from his saying that the reefs are at one time covered and at another time bare, and from his calling the ocean a river, he infers that its flowing character regarding the tides is indicated. Now, the first point is good, but the second has no reason; for the onset of the tide does not resemble a river current, and much more the retreat is not of such a kind, and the argument of Crates teaches something more plausible. For he calls the whole ocean “deep-flowing” and “backward-flowing,” and likewise a “river”; but he also calls some part of the ocean a “river” and the “flow of a river,” not of the whole but of the part, when he says: “But when the ship left the flow of the river Oceanus, and came to the wave of the wide-wayed sea.” For he does not mean the whole, but the “flow of the river in the ocean,” which is a part of the ocean, which Crates says is an overflow and a gulf extending from the winter tropic towards the south pole. For one could leave this and still be in the ocean, but it is impossible for one who has left the whole to still be in the whole. Yet Homer says: “left the flow of the river, and came to the wave of the sea,” which is none other than the ocean. It follows, then, if you accept the other view, that having gone out of the ocean he came into the ocean. But these matters belong to a longer discussion.

​On the other hand, that the inhabited world is an island must be grasped first from sensation and experience. For everywhere, wherever it has been possible for men to advance to the limits of the earth, the sea is found, which we indeed call the ocean. And where it was not possible to grasp it by sensation, reason demonstrates it. For the eastern side, that of the Indians, and the western side, that of the Iberians and the Maurusians, are entirely sailed around for a great distance both on the southern side and the northern. And the remaining part, which has been unnavigable for us until now because no persons sailing from opposite directions have met each other, is not great, if one estimates it from the parallel distances accessible to us. And it is not likely that the Atlantic Sea is divided into two seas, separated by isthmuses so narrow as to prevent the circumnavigation, but rather that it is confluent and continuous; for those who attempted to sail around and then turned back say that they were not driven back by any opposing continent that blocked their further voyage, but by want and solitude, although the sea offered a passage no less. And this agrees more with the phenomena of the ocean regarding the ebb and flow; at any rate, the manner of the changes and of the increases and decreases is everywhere the same, or does not differ much, as if the movement were performed on a single sea and from a single cause.