OBREGÓN, ALVARO (1880- ), Mexican President, was born in Nogales, Sonora, Mexico, in 1880, of Basque and Yaqui parentage. He engaged in farming, trading, and stock-raising in Sonora. He took part in the Madero revolution when Pascual Orozco threatened invasion of his state, driving the rebels out with a troop of 400 Yaquis. He joined Carranza against Huerta in 1913, winning general's rank by defeating the latter. In 1914, leading Constitutionalist forces in the West, he took Sinaloa, Culiacan and Guadalajara in July, entering the capital Aug. 15. He sided with Carranza against Villa, took Puebla in Jan. 1915, and held the capital when the generals of the Convention left for Aguascalientes Jan. 27, but moved out March 10. He won victories over Villa at Celaya April 19; at Leon, where he lost his right arm, on June 4; and at Torreon and Saltillo in Sept. As Carranza's Minister of War he negotiated with Gens. Scott and Funston for the withdrawal of Pershing's expedition in 1916. Disagreeing with the President, he resigned and returned to his estate May i 1917. There he accumulated a fortune by control of the garbanzo (chick-pea) crop of the W. coast. In June 1918 he became a candidate for the presidency against Gen. Pablo Gonzalez and Ignacio Bonillas. In the same year he visited the United States. In March 1920 Carranza's attempts to control Sonora against Obregon's candidacy, and the arrest of the latter charged with rebellion, led him, on escaping from Mexico City, to raise a revolt which began in Sonora under the Plan of Agua Prieta on April 9. After rapid successes Obrcgon entered Mexico City May 8, Car- ranza having fled on the 5th. Adolfo de la Huerta, Obregon's lieu- tenant, was made provisional president, Obregon being elected President in Sept. and inaugurated Dec. i. (See MEXICO.)
O'BRIEN, PETER O'BRIEN, 1ST BARON (1842-1914), Irish lawyer and Lord Chief Justice, was born June 29 1842, the fifth son of John O'Brien, M.P. for Limerick from 1841 to 1852. He was educated at Trinity College, Dublin, and was called to the Irish bar in 1865. He became a Q.C. in 1880, was in 1883 made Crown prosecutor and serjeant-at-law, and in 1884 became a bencher of King's Inns. In 1886 he opposed the Home Rule bill, and joined the Unionist party, becoming in 1887 solicitor- general and in 1888 attorney-general for Ireland, in which capacity he conducted many political prosecutions. He earned at this time his nickname of "Peter the Packer." In 1889 he was made Lord Chief Justice of Ireland, was created a baronet in 1891, and was raised to the peerage in 1900. He retired from the office of Lord Chief Justice in 1913, and died at Stillorgan, co. Dublin, Sept. 7 1914, his title becoming extinct.
OCEANOGRAPHY (see 19.967*). The period foUowing the year 1910 was not productive of notable additions to knowledge of general oceanography. Several expeditions were made just before that year and in the period between then and the World War. The most important were: the Australian Antarctic expe- dition of 1911-4 under Sir Douglas Mawson; the Danish Ocean- ographical expeditions in the Mediterranean and adjacent seas of 1908-10; a short cruise made by Sir John Murray and Dr. Johan Hjort in the Norwegian Fishery exploring vessel " Michael Sars" in 1910, the general results of which were pub- lished as The Depths of the Ocean (1912) by the leaders of the expe- dition; and a short special cruise made by the " Scotia " in 1913 (after the loss of the " Titanic ") under the leadership of Dr. Matthews, which made observations upon the distribution of ice in the North Atlantic.
Generally, oceanographic work at sea was brought to a stop by the outbreak of war in 1914. A good deal of special investiga- tion relating to naval and especially submarine warfare was carried on during 1914-8, but the results of this confidential work were not published. The very important activities of the Conseil Permanent International pour 1'Exploration de la Mer were suspended during the war except in a few local seas. Fortunately the continuity of the organization was maintained, largely
through the mediation of the British Government, and the council held its first post-war meeting in London in 1920. Its work is primarily that of the investigation of the fisheries of northern Europe, but its general methods are oceanographical, and its published results have formed an immense contribution to the science. Germany and Russia had, temporarily at all events, withdrawn from the cooperation, but France came in for the first time in 1920, and it was understood that the United States was likely to join in the scheme of investigation. An entirely new project was an international survey of the Mediterranean and adjacent seas, from the fishery and oceanographical stand- points, by France, Italy, Spain and Portugal, but in 1921 no defi- nite programme had been put in operation. The International Research Council formed just after the war constituted a sec- tion for Physical Oceanography, which held its first meeting in Paris in 1921. In 1920 a very influential movement began, in England, for the despatch of a new " Challenger " expedition on a great scale, but it was suspended in 1921 for lack of funds. On the whole, oceanographical research was being taken up most actively in Europe, but much important work was also begun in America, for instance the fine hydrographical research in the Pacific by the Scripps Institute of the university of California.
Methods of Investigation. Little change occurred subse- quently to 1910 with regard to the methods of oceanographical investigation except a continual refinement and an increasing improvement in the apparatus used: in this direction the activi- ties of the Central Bureau of the International Council were very noteworthy. The instruments current -meters, sounding apparatus, water-collecting bottles, thermometers, hydrometers, etc. were all elaborated and improved. Hydrodynamical meth- ods received increased attention and the investigation of the movements of the ocean by means of physico-mathematical devices developed as a result of the older work of Bjerknes, con- tinued chiefly by Helland-Hansen and Sandstrom. It became fairly certain, however, that theory had outrun observational work, and that the latter must again receive renewed attention.
The empirical data on which the hydrodynamical investigations are based are: (i) observed velocities and directions of oceanic currents and drifts; (2) salinity; (3) density; (4) temperature of the sea water in situ; (5) oceanic soundings. Given that such observations at the surface of the sea, at intermediate levels and at the bottom are sufficiently numerous and are of a high degree of precision, general conclusions as to the movements of the ocean may be deduced from established theorems in hydrodynamics. But detailed studies of the circulation of the water in any small area show deviations from the calculated results that are to be expected: thus Nansen's investigation of the Norwegian sea shows that the main directions of streaming of the water are broken up by numerous large and small vortices. So also any exhaustive .survey of the temperature and salinity of the sea at a great number of points on and below the surface reveals a complexity of conditions that may defy mathematical analysis and could not easily be predicted. A very large amount of local detailed observation in the various sea-areas must be the next important work to be undertaken : this means current-observations by direct readings of metres, by the employment of drift-bottles and numerous determinations of temperature and salinity at all seasons.
Variations in Oceanic Circtilation.The general scheme of oceanic circulation was made out prior to 1910. The excess of heat received in equatorial regions expands the water, but at the same time excess of evaporation concentrates it, so that the density increases. The heating effect is, however, the more significant, and so the water of the ocean tends to flow N. and S. from the equator towards the poles. In intermediate latitudes there is a loss of heat and then the. increased density due to equatorial concentration becomes a factor. The water sinks below the surface and continues to flow along the sea bottom back towards the equator. In the polar areas the melting of sea-ice and of ice formed by precipitation lowers the density of the seawater and causes a difference of level which sets up streaming movements towards the equator. This surface drifting water is cold and as it enters into intermediate zones it remains colder
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