Page:Physical Geography of the Sea and its Meteorology.djvu/30

4 been by no means completed—no, not even to the tenth part—yet more knowledge has been gained concerning the depths and bottom of the deep sea, than all the world had before acquired in all previous time.

10. Its probable depth. "The system of deep-sea soundings thus inaugurated does not thus far authorize the conclusion that the overage depth of ocean water is more than three or four miles (§ 3) nor have any reliable soundings yet been made in water over five miles deep.

11. Relation between its depth and the waves of the sea.—In very shallow pools, where the water is not more than a few inches deep, the ripples or waves, as all of us, when children, have observed, are small; their motion, also, is slow. But when the water is deep, the waves are larger and more rapid in their progress, thus indicating the existence of a numerical relation between their breadth, height, and velocity, and the depth of the water. It may be inferred, therefore, that if we knew the size and velocity of certain waves, we could compute the depth of the ocean.

12. Airy's wave tables.—Such a computation has been made, and we have the authority of Mr. Airy, the Astronomer Royal, that waves of given breadths will travel in water of certain depths with the velocities as per table:

13. The earthquake of Simoda.—Accident has afforded us an opportunity of giving a quasi practical application to Mr. Airy's formulæ. On the 23rd of December, 1854, at 9.45, the