The line between these various branches of science is for our present purpose difficult to draw; but at the risk of a charge of arbitrary treatment it appears pertinent to refer to certain facts in the history of oceanography. As an organized department this is no less a creation of the nineteenth century than others we have named. Among ancient geographers there was certainly some speculation as to the physical character of the seas, known and unknown. From a very early period sounding in shallow waters has been recognized as a method of navigation, and Strabo, for example, displays some knowledge of the greater depths of the Mediterranean. But to mere navigation a close study of the sea was not essential, and explorers with their eyes fixed on distant lands were concerned merely to make the best of their way over the intervening waters. It is not, therefore, until towards the close of the eighteenth century, the period of the scientific exploration of the Arctic region and of Cook’s great voyages--exploration necessarily carried out mainly on shipboard--that any systematic investigation of the deep seas is found. Phipps, Scoresby, John and James Clark Ross, and especially the last, made deep soundings; but the whole subject of oceanography may be said to have been first organized by Matthew Fontaine Maury (1806–73), an American naval officer, who, after his appointment to the United States Dépôt of Charts and Instruments (which became the Hydrographic Office), systematized the collection of navigators’ observations on winds and currents, while his example inspired the establishment of similar collections in other countries. He also devoted himself to the study of the relief of the ocean floor, an investigation which was forwarded by the invention of a compatriot, J. M. Brooke, of the United States Navy, who introduced the principle of sounding in great depths by means of a lead which was detached from the line on reaching the bottom, so that the line might be easily hauled aboard. Maury published his _Physical Geography of the Sea_ in 1855. Meanwhile the possibility of connecting England and America by submarine telegraphic cable had been discussed ten years earlier. Communication across the Channel with France had been successfully established in 1851, and in 1856 the first signals passed across the Atlantic. This first trans-oceanic cable survived only for a little, but the investigation of the sea-floor had now acquired a commercial as well as a scientific interest.