Page:Physical Geography of the Sea and its Meteorology.djvu/27



§ 1.The two oceans of air and water.—Our planet is invested with two great oceans; one visible, the other invisible; one is underfoot, the other overhead; one entirely envelops it, the other covers about two-thirds of its surface. All the water of the one weighs about 400 times as much as all the air of the other.

2.Their meeting.—It is at the bottom of this lighter ocean where the forces which we are about to study are brought into play. This place of meeting is the battle-field of nature, the dwelling-place of man; it is the scene of the greatest conflicts which he is permitted to witness, for here rage in their utmost fury the powers of sea, earth, and air; therefore, in treating of the Physical Geography of the sea, we must necessarily refer to the phenomena which are displayed at the meeting of these two oceans. Let us, therefore, before entering either of these fields for study, proceed first to consider each one in some of its most striking characteristics. They are both in a state of what is called unstable equilibrium; hence the currents of one and the winds of the other.

3.Their depth.—As to their depth, we know very little more of the one than of the other; but the conjecture that the average depth of the sea does not much exceed four miles is probably as near the truth as is the commonly received opinion that the height of the atmosphere does not exceed fifty miles. If the air were,