GEOGRAPHICAL PROGRESS AND DISCOVERY. 



351 



to private life. He was the author of a num- 

 ber of valuable historical works, including 

 "History of the Revolution of 1848 " (8 vols., 

 1881-'62), "History of the Executive Com- 

 mittee " (1869), and " The June Days " (1873). 

 GEOGRAPHICAL PROGRESS AND DIS- 

 COVERY. The number of exploring expedi- 

 tions and the extent of their tasks increase from 

 year to year, although the great geographical 

 outlines, the boundaries of the river basins and 

 the courses of mountain chains, the lines of the 

 seacoast and the positions of islands, are nearly 

 all determined, except in the frozen polar re- 

 gions and in the yet inaccessible interiors of the 

 great continents. The sciences of geology, bot- 

 any, and zoology, ethnology, meteorology, and 

 hydrography, are all investigated by competent 

 scholars in the larger expeditions ; and every 

 phenomenon and product of the earth, air, or 

 water, noted and studied. Although the expe- 

 ditions in many instances fail of reaching the 

 particular geographical goal or solving the par- 

 ticular problem which they set before them, 

 they often obtain results which in the general 

 interests of science are of more value than the 

 accomplishment of their ostensible purpose; 

 yet these achievements are generally so involved 

 in the complicated development of the sciences 

 that they furnish no salient facts for the popu- 

 lar mind to lay hold of. The depths and hy- 

 drography of the ocean, having a practical bear- 

 ing on navigation, are being investigated by 

 naval vessels of nearly every principal nation. 

 These expeditions afford scientists an opportu- 

 nity to study the living inhabitants of the ocean 

 and the geological formation of sedimentary 

 rock as it is actually going on in our period, 

 and also the geology, botany, zoology, and eth- 

 nology of the islands and shores touched at in 

 the voyages. The Russian operations in Asia, 

 and the rivalry between that Government and 

 England, each seeking to extend its influence 

 among the semibarbarous peoples of the cen- 

 tral portions of that continent, have thrown 

 new light on one of the most interesting regions 

 of the globe, as well from an ethnological and 

 historical point of view as from that of geology 

 and physical geography. The proportion in 

 the regions recently discovered of lands which 

 are not only habitable but temperate and fruit- 

 ful is most gratifying in lengthening the vista 

 of our prophetic hopes in the future of the hu- 

 man race and the possibilities of civilization. 

 Such promising regions have been discovered 

 not only in the interior of Africa, but in New 

 Guinea and other Pacific islands, in Patagonia 

 and the center of South America, in the interi- 

 or of Asia, and elsewhere, as to enlarge very 

 considerably the extent of the habitable land 

 known. 



Sir Wyville Thomson, in his address as pres- 

 ident of the geographical section of the British 

 Association, summed up the recent improve- 

 ments in hydrographical knowledge. The ocean 

 must be considered as one and continuous. It 

 covers almost entirely one hemisphere of the 



globe; and the Atlantic with the Arctic Sea 

 and the North Pacific are only gulfs which run 

 out of it to the northward. The sheet of wa- 

 ter covering the ocean hemisphere, thin as it 

 is compared with the earth's radius, is divided 

 into two layers : at a varying depth, which av- 

 erages perhaps 500 fathoms, is the stratum of 

 water having the temperature of 40 Fahr. ; this 

 may be taken as the division between the two 

 layers, the upper of which varies greatly in 

 temperature in different regions, while the low- 

 er one grows gradually and slowly colder, with 

 increasing slowness downward, to a minimum 

 at the bottom. The paramount cause of move- 

 ments in the upper stratum is the trade winds 

 and their modifications and counter-currents : 

 the great equatorial current driven from east to 

 west in the northern ocean region impinges on 

 the eastern coasts of the continents ; a branch 

 is deflected to the north, and makes a curve 

 around the closed end of the Pacific, tending to 

 sweep back down the North American coast ; 

 in the Atlantic the Gulf Stream skirts along 

 the shores of northern Europe, a branch shoot- 

 ing off into the arctic basin and keeping par- 

 tially open the passage through the polar ice 

 into Behring's Straits ; the southern deflections 

 are neutralized by the southern anti-trade 

 winds. Of the lower layer of the ocean recent 

 investigations have proved that the whole mass, 

 often 2,000 fathoms in thickness, has a slow 

 and constant flow to the northward, and that 

 the depths of the Pacific, Indian, and Atlantic 

 Oceans are fed by the waters of the antarctic 

 seas: this is shown by the facts that the cold 

 lower strata increase perceptibly in tempera- 

 ture to the northward, and the continuity of 

 every layer with a corresponding layer in the 

 southern sea is established. This movement 

 must be due to another unexpected phenome- 

 non : evaporation must be in excess of precipita- 

 tion in the northern parts of the land-hemi- 

 sphere, and the subtracted vapor must be con- 

 veyed by the upper currents of the air to the 

 zone of low barometric pressure in the south, 

 and precipitated in the form of snow or rain, 

 ascending northward again in the deepest chan- 

 nels of the ocean on account of its low temper- 

 ature and consequent greater specific gravity. 

 When this northward movement passes over 

 obstructions such as submarine mountain ridges, 

 whatever be the depth of the seas beyond, the 

 temperature at the bottom will correspond to 

 that of the layer of water which strikes the 

 summit of the barrier. The most notable in- 

 stance of this is the case of the series of closed 

 submarine basins of different temperatures in 

 the Malay Archipelago. The average depth of 

 the ocean is a little over 2,000 fathoms. There 

 is probably nowhere a greater depth than 5,000 

 fathoms. Local depths of over 4,000 fathoms 

 are found but rarely, and seem to be in most 

 cases pits in the vicinity of volcanic islands. 

 But in all the ocean basins extended depres- 

 sions of 3,000 fathoms or a little more are 

 found, which run, with some degree of regular- 



