If we look upon the map of the world, we shall find that the ocean occupies a considerably greater surface of the globe than the land is found to do. Although the ocean, properly speaking, is but one extensive sheet of water, continued over every part of the globe without interruption; and although no part is divided from the rest, yet geographers have distinguished it by different names, as the Atlantic or Western Ocean; the Northern, Southern, Pacific, Indian, and German Oceans. In this vast receptacle, almost all the rivers of the earth ultimately terminate. And yet these vast and inexhaustable supplies do not seem to increase its stores; for it is neither apparently swelled by their tribute, nor diminished by their failure; it continues constantly the same. Indeed, the quantity of water of all the rivers and lakes in the world is nothing compared to that contained in this prodigious reservoir. And some natural philosophers have carried their ideas on this subject so far as to assert, in consequence of certain calculations, that, if the bed of the sea were empty, all the rivers of the world flowing into it with a continuance of their present stores, would take up at least 800 years to fill it again to its present height.[75] To ascertain the _depth_ of the sea has been found impracticable, both on account of the numerous experiments which it would be found necessary to make, and the want of proper instruments for that purpose. Beyond a certain depth the sea has hitherto been found unfathomable; and though several methods have been contrived to obviate this difficulty, none of them has completely answered the purpose. We know in general that the depth of the sea increases gradually as we leave the shore; but if this continued beyond a certain distance, the depth in the middle of the ocean would be prodigious. Indeed, the numerous islands every where scattered in the sea demonstrate the contrary, by showing us that the bottom of the water is unequal like the land, and that so far from uniformly sinking, it sometimes rises into lofty mountains. If the depth of the sea be in proportion to the elevation of the land, as has been generally supposed, its greatest depth will not exceed five or six miles; for there is no mountain six miles perpendicular above the level of the sea. The sea has never been actually sounded to a greater depth than a mile and 66 feet; every thing beyond that, therefore, rests entirely upon conjecture and analogical reasoning, which, in this case, are in no wise conclusive. Along the coasts, where the depth of the sea is generally well known, it has always been found proportioned to the height of the shore; when the coast is high and mountainous, the sea that washes it is deep; when, on the contrary, the coast is low, the water is shallow. Whether this analogy holds at a distance from the shore, experiments alone can determine.