SOUND, SOUNDING (OF., Fr. sonde-, prob ably from Lat. sub, under undarc, to undulate, from unda, wave; less plausibly from AS., Icel. send, Ger. Send, sound. strait). The operation of ascertaining the depth of water. In shallow waters (less than 20 fathoms) the depths are ascertained with the lead and line (see LEAD, SOUNDING) ; in greater depths the deep-sea had and line are used or else a sounding machine. Beyond a depth of 200 fathoms soundings are not useful for the purpose of navigating vessels: but 'deep-sea' soundings are taken in all depths in order to ascertain the shape and character of the ocean bottom and its organisms, living and dead. See DEEP-SEA EXPLORATION.
Few attempts to ascertain the depth of the (wean were made before the beginning of the nineteenth century, and it was not until toward the middle of it that the investigations were at all systematic. The disadvantges under which the earlier expeditions labored were such as to preclude not only rapid hut reliable work. For the lines rope of ordinary character was used, and the sinkers employed were generally too light. The weight of the rope after it became water soaked was very great, and its bulk, together with that of the reels, very troublesome. The inadequate sinkers caused the line to run out very slowly, and the reeling in was both laborious and, tedious. Owing to the difficulty of holding a large sailing ship in a fixed position for the requisite time and the amplitude of her movements on the waves, many of the soundings were made from boats, which still further reduced the speed, es pecially that of preparing to cast and of reeling in. The first attempt (so far as known) to use wire for the line was that of the well-known 'ex ploring expedition' sent out by the United States Navy Department in 1838. The wire was of copper, about 3-32 of an inch in circumference, with sol dered and twisted splices. Owing to lack of proper appliances for handling, it always broke at 500 to 1000 fathoms, and its use was aban doned. In August, 1894, Captain Barnet. R. N.. made a sounding in 2000 fathoms with iron wire. This also broke, and no more attempts with it were made. Three months later. Lieut. J. O. Walsh, U. S. N., in the United States schooner Taney, tried to use steel wire, but his efforts were unsuccessful, the wire being too large and the sinkers too small. Ile reported soundings of 5700 fathoms and no bottom. but the depth was actually less than half as great.
Much work continued to he done with rope lines both before and after these experiments, but more especially afterwards. In 18-10 Cap tain James F. Ross first noted time intervals in sounding; he also used very heavy sinkers. and his results were exceedingly accurate for those days. The question of time intervals was taken up and perfected by Lieutenant (afterwards Ad miral) Taylor, and other officers of the United States Navy. and their observations were of great importance in determining the accuracy of deep-sea work before the invention of the Thomson sound ing machine. For a time the United States Department abandoned the use of both wire and rope, and. at the instance of Lieutenant "Maury,
adopted waxed flax twine. weighing only nine pounds to the statute mile. Between 1851 and 1853 much 'of the Atlantic was explored by United States vessels and hundreds of soundings taken (using the twine mostly) with fairly accu rate results, though, as no specimens of the bot tom were obtained, they were open to question. In 1853-54 Passed Midshipman J. M. Brooke, U. S. N., brought out his cup and detachable sinker, which enabled specimens of the bottom to be ob tained while using a heavy weight to keep the line taut when running out. Brooke also devel oped his table of 'standard casts' utilizing the time interval and weight of line out, and lie much improved the sounding apparatus.
The Civil War put an end to the deep-sea work of the United States Navy for many years, but it was carried on most successfully by the British, especially by Captain (afterwards Admiral) F. P. Shortland, who improved the Brooke sounding machine, and was one of the first, if not the first, to enunciate the important rule in regard to ten sion on the line, viz., "A sounding line should not he permitted to run free, but should be resisted by a force equal to the weight in water of a length of the line equal to the depth to be deter mined." The success of. the Brooke device and its modifications in bringing up specimens of the bottom and its organisms attracted the attention of naturalists and geologists, and their curiosity caused dredging in great depths to be attempted. The results of the early (1867-69) work of Count Ponrtales under the direction of the United States Coast Survey brought about renewed interest by showing, as Ponrtales says, "that animal life exists at great depths in as great an abundance as in shallow water." In 1872 the British Gov ernment fitted out the celebrated Challenger Ex pedition (q.v.) for investigating everything con nected with the ocean depths. Strange to say, although Sir William Thomson had invented his sounding machine and submitted it to the British Admiralty several months before the Challenger was ready, it was rejected for imperfections which might have been easily corrected, and the Challenger sailed with her antiquated outfit of sounding material, whereby a vast amount of time was lost as well as space for supplies and specimens. The United States ship Tuscarora under Captain Belknap sailed from San Francisco only four months after the Challenger, but the United States Navy Department was wise enough to supply hem with one or more Thomson ma chines in addition to the ordinary rope outfit. The new machines were not entirely satisfactory at the start, hut were easily brought into work ing shape by the Tuscarora's officers, and after very few trials entirely superseded the old ap paratus. Since that time all deep-sea work has been done by machines, and thousands of sound ings have been taken to determine the location of the submarine cables which have now become so numerous.