man Brooke, of the United States Navy, who made the first great improvement in deep-sea sounding in 1854 by inventing a machine in which, applying Causanus's idea of disengaging a weight attached to the sounding line, the sinker was detached on striking the bottom and left behind when the tube was drawn up. The 
arrangement of the parts is shown in the accompanying figure. When the tube B strikes the bottom, the lines A A slack and allow the arms C C to be pulled down by the weight D. When these arms have reached the positions indicated by the dotted lines, the slings supporting the weight have slipped off, and the tube can be hauled up, bringing within it a specimen of the bottom. This implement has been improved from time to time by various officers of our own and foreign navies by changing the manner of slinging and detaching the sinker, and by adding valves to the upper and lower ends of the tube to prevent the specimen from being washed out during the rapid ascent which has been rendered possible by the use of wire sounding line and steam hoisting engines; but in all the essential features it is the same as the most successful modern sounding apparatus. The impulse given to deep-sea sounding by Brooke was seconded by the successful adaptation of pianoforte wire to use as a sounding line, in 1872, by Sir William Thomson; and within recent years soundings have been taken far and wide in all the seas by national vessels during their cruises, by vessels engaged in laying submarine cables, and by various specially organized expeditions, among which that known as the Challenger Expedition, sent out by the Government of Great Britain during the period from 1873 to 1876, stands pre-eminent. As a result of this work many of the questions which perplexed the naturalists of the middle of the present century have now been cleared away.
Many of the specimens of the bottom that were brought up in the early days of deep-sea sounding were studied through the microscopes of Ehrenberg, of Berlin, and Bailey, of West Point. Maury, who believed that there are no currents and no life at the bottom of the sea, wrote: "They all tell the same story. They teach us that the quiet of the grave reigns everywhere in the profound depths of the ocean; that the repose there is beyond the reach of wind; it is so perfect that none of the powers of earth, save only the earthquake and volcano can disturb it. The
