DEPTH OF THE OCEAN THEORY OP WAVES The depth of various parts of the ocean have also been approximately determined by observations on waves, and the results, thus obtained, agree in a very remarkable manner with the latest reliable "soundings." The Astronomer-Royal, Sir G. Airy, first propounded the theory that a definite relation exists between the breadth and velocity of a wave, and the depth of the water over which it travels. The results of his researches are embodied in the three laws known as the "Theory of Waves," briefly stated as follows :—(1) Waves of any breadth may be formed in water of any depth. (2) A wave of a given breadth cannot attain more than a certain velocity. (3) When the depth is less than the breadth, the
motion increases nearly up to a certain velocity.
In two practical applications of the " Theory of Waves," to determine the depth of the Atlantic and Pacific Oceans, the tidal wave was selected in the former, and the great earth quake wave of 1854 in the latter. Herschel thus estimated the depth of the Atlantic at 22,157 feet, a number rather in excess of that given by the Challenger expedition, viz , 2500 fathoms, or 15,000 feet. The average depth of the Pacific was found to be 14,190 feet, which closely approximates that given by the Challenger, viz., 2,400 fathoms, or 14,400 feet.