Page:EB1911 - Volume 19.djvu/1008

 level; thus fifteen years’ observations at Aden show a maximum in May at the end of the north-east monsoon, and a rapid falling off after the beginning of the south-west monsoon to a minimum in August, the total range being 9 in. The influence of wind on water-level is most remarkable in heavy storms on the flat coasts of the North Sea and Baltic, when the rise may amount to very many feet. In the region of tropical hurricanes the converging wind system of a circular storm causes a heaping up of water capable of devastating the low coral islands of the Pacific. On the 1st of November 1876 a cyclone acting in this way submerged a great area of the level plain of the Ganges delta to a depth of 46 ft.; here the influence of the difference of pressure within and without the cyclone acted in the same direction as the wind. The old speculations as to a great difference of level between the Mediterranean and the Red Sea, and on the two sides of the Isthmus of Panama, which hindered the projects for canals connecting those waters, have been proved by modern levelling of high precision to be totally erroneous.

Deep-sea Soundings.—The hand-lead attached to a line divided into fathoms was a well-known aid to navigation even in high antiquity, and its use is mentioned in Herodotus (ii. 5) and in the Acts of the Apostles (xxvii. 29). Greater depths than those usually sounded by a hand-line may possibly not have been beyond the reach of the earlier navigators, for Strabo says “of measured seas the Sardonian is the deepest with full one thousand fathoms” (i. 3, p. 53 Cas.). Yet we find that the great discoverers of the modern period were only familiar with the hand-lead, and the lines in use did not exceed 200 fathoms in length. Ingenious devices had indeed been tried in the 17th century and earlier, by which a lead thrown into the sea without a line detached a float on striking the bottom, and it was proposed to calculate the depth by the time required for the float to reappear. The earliest deep-sea sounding on record is that of Captain Phipps on the 4th of September 1773 in the Norwegian Sea, in 65° N. 3° E., on his return from his expedition to Spitsbergen. He spliced together all the sounding-lines on board, and with a weight of attached he found bottom in 683 fathoms and secured a sample of fine soft blue mud. He detected the moment of the lead touching the bottom by the sudden slackening in the rate at which the line ran out. Polar explorers frequently repeated those experiments in deep-sea soundings, both William Scoresby and Sir John Ross obtaining notable results, though not reaching depths of more than 1200 fathoms. The honour of first sounding really oceanic depths belongs to Sir James Clark Ross, who made some excellent measurements in very deep water, though in a few instances he overestimated the depth by failing to detect the moment at which the lead touched bottom. The pursuit of these isolated investigations received a great impetus from the enthusiasm of the great American oceanographer Captain Matthew Fontaine Maury, U.S.N., who directed the whole impetuous strength of his character to the task of compelling the silent depths of the ocean to tell their tale. Instead of the expensive mile-long stout hemp lines used by Ross, Maury introduced a ball of strong twine attached to a cannon shot, which ran it out rapidly; when the bottom was reached the twine was cut and the depth deduced from the length of string left in the ball on board. The time of touching bottom was judged by timing each 100-fathom mark and noting the sudden increase in the time interval when the shot reached the bottom. Maury, however, recognized that in great depths the surest guarantee of bottom having been reached was to bring up a sample of the deposit. To do this with a heavy lead attached required a very strong hemp line, and the twine used in the American method was useless for this purpose. In 1854 J. M. Brooke, a midshipman of the U.S.N., invented the principle already foreshadowed by Nicolaus Cusanus in the 15th century and by Robert Hooke in the 17th, of using a heavy weight so hung on the sounding-tube that it was automatically released on striking the bottom and left behind, while the light brass tube containing a sample of the deposit was easily hauled up. This principle has been adopted universally for deep soundings, and is now applied in many forms. In 1855 Maury published

the first chart of the depths of the Atlantic between 52° N. and 10° S. At this period an exact knowledge of the depths of the ocean assumed an unlooked-for practical importance from the daring project for laying a telegraph cable between Ireland and Newfoundland. Deep soundings were made in the Atlantic for this purpose by vessels both of the British and of the American navies, while in the Mediterranean and in the Indian Ocean many soundings were made in connexion with submarine cables to the East. Another stimulus came from the biologists, who began to realize the importance of a more detailed investigation of the life conditions of organisms at great depths in the sea. The lead in this direction was taken by British biologists, beginning with Edward Forbes in 1839, and in 1868 a party on board H.M.S. “Lightning” pursued researches in the waters to the north of Scotland. In 1869 and 1870 this work was extended to the Irish Sea and Bay of Biscay in H.M.S. “Porcupine,” and to the Mediterranean in H.M.S. “Shearwater.” The last-named vessel secured 157 trustworthy deep soundings, with samples of the deposits, and also observations of temperature and salinity in different depths, as well as dredging for the collection of the organisms of the deep sea.

These preliminary trips of scientific marine investigation were followed by the greatest purely scientific expedition ever undertaken, the voyage of H.M.S. “Challenger” round the world under the scientific direction of Sir Wyville Thomson and the naval command of Sir George Nares. This epoch-making expedition lasted from Christmas 1872 to the end of May 1876, and gave the first wide and general view of the physical and biological conditions of the ocean as a whole. Almost simultaneously with the “Challenger,” a German expedition in S.M.S. “Gazelle” conducted observations in the South Atlantic, Indian and South Pacific Oceans; and the U.S.S “Tuscarora” made a cruise in the North Pacific, sounding out lines for a projected Pacific cable. The successor of Sir Wyville Thomson in the editorship of the “Challenger” Reports, Sir John Murray, has rightly said that since the days of Columbus and Magellan no such revelation regarding the surface of our planet had been made as in that eighth decade of the 19th century. Since that time the British cable-ships have been busy in all the oceans making sections across the great expanses of water with ever-increasing accuracy, and in that work the government surveying ships have also been engaged, vast stretches of the Indian and Pacific Oceans having been opened up to knowledge by H.M.SS. “Egeria,” “Waterwitch,” “Dart,” “Penguin,” “Stork,” and “Investigator.” American scientific enterprise, mainly under the guidance of Professor Alexander Agassiz, has been active in the North Atlantic and especially in the Pacific Ocean, where very important investigations have been made. The eastern part of the North Atlantic has been the scene of many expeditions, often purely biological in their purpose, amongst which there may be mentioned the cruises of the “Travailleur” and “Talisman” under Professor Milne-Edwards in 1880–1883, and since 1887 those of the prince of Monaco in his yachts, as well as numerous Danish vessels in the sea between Iceland and Greenland, conspicuous amongst which were the expeditions in 1896–1898 on board the “Ingolf.” The Norwegian Sea was studied by the Norwegian expedition on board the “Vöringen” in 1876–1878, and the north polar basin by Nansen and Sverdrup in the “Fram” in 1893–1896, the Mediterranean by the Italians on the “Washington” and by the Austrians on the “Pola” in 1890–1893, the latter carrying the investigations to the Red Sea in 1895–1898, while the Russians investigated the Black Sea in 1890–1893. For high southern latitudes special value attaches to the soundings of the German deep-sea expedition on the “Valdivia” in 1898–1899, and to those of the “Belgica” in 1897–1898, the “Gauss” in 1902–1903, and the “Scotia” in 1903–1904. The soundings of the Dutch expedition on the “Siboga” during 1899–1900 in the eastern part of the Malay seas and those of the German surveying ship “Planet” in 1906 in the South Atlantic, Indian and North Pacific Oceans were notable, and Sir John Murray’s expedition on the “Michael Sars” in the Atlantic in 1910 obtained important results.