N since the great Challenger expedition of I872-I876, only the merest beginning has been made in the study of the open sea. Even with regard to such simple features as depths, deposits, and currents is this true. Extensive areas, covering thousands of square miles, have never been sounded; the exact nature of oceanic deposits is still problematic, since the bottom has been merely scratched and in but relatively few places; the variations to which the different ocean currents are subject, especially within the depths, are almost wholly unknown. The paucity of our knowledge of the open sea arises primarily from the fact that an oceanographic expedition of wide scope is a costly undertaking, since it necessarily involves a considerable period of time, a relatively large personnel, expensive specialized apparatus, and a well-equipped vessel. Such an expedition is altogether beyond the means of the individual oceanographer, requiring the sponsorship of some governmental agency or the resources of a well endowed institution. The need for extensive oceanographic research, however, has become more and more urgent and in the last decade has aroused world-wide discussion. At the meeting of the British Association for the Advancement of Science held at Cardiff in August, I920, a resolution was adopted urging the initiation of a national expedition for the exploration of the ocean similar in character to that of the Challenger expedition. A memorandum drawn up1 estimated the cost of the proposed expedition at more than a million dollars, apart from the vessel, which it was hoped would be provided by the British Admiralty. Widespread interest was aroused, not only in Great Britain but throughout the world. Financial considerations, however, necessitated the abandonment of the project. In the United States a similar discussion was brought to a head at a conference on oceanography convened by the Secretary of the Navy at Washington in July, 1924.2 But, like the proposed British expedition, this plan for an American national expedition was never carried into execution. In the two wealthiest maritime countries it was thus found impossible to launch a program of oceanographic research of a national character. Fortunately, however, such projects were found to be within the means of Germany, Denmark, Holland, and the Carnegie Institution of Washington. To a review of the work of these four expeditions the present article is devoted.