Geography of the Sea. 139 



tific observations in all parts of the world. Continued improve- , 

 ments in the appliances and instruments have made the results 

 more precise than was possible in the earlier times, and, as the 

 data accumulate, the bathymetric charts of the oceans are be- 

 comins: more accurate. Not until this work is much further ad- 

 vanced, however, shall we be able to arrive at an estimate of the 

 depths and weights of the oceans at all comparable to our knowl- 

 edge of the heights and weights of the various great land masses 

 above sea level. 



Other important results of these expeditions have been the 

 verification of many reported elevations of the ocean bed formerly 

 considered doubtful, the discovery of new ones, and proof of 

 the non-existence of others, which had been reported as dangers 

 to navigation. 



The Geography of the Sea reached a decidedly more advanced 

 stage by the inception of several great scientific expeditions, of 

 which that of the Lightning, in 1868, to the Hebrides and Faroe 

 Islands, under the superintendence of Professors Carpenter and 

 Wyville Thompson, was the forerunner. This was followed by 

 the three years' cruise of the Challenger (Br.) in 18*73-75, the 

 Tuscarora (Am.) in 1874, and the Gazelle (Ger.) in 1875, by those 

 despatched under the authority of the U. S. Coast Survey and of 

 the U. S. Fish Commission, and others of lesser importance, sent 

 out under the auspices of European governments, and by private 

 individuals. All of these have contributed in an eminent degree 

 to the progress of the science by giving us a better understanding 

 of the physical and biological conditions of the sea at all depths. 

 Special mention must be made of the splendid work that is being 

 done continually by the expeditions sent out by the TJ. S. Fish 

 Commission. This branch of the United States service, originally 

 established for the investigation of the causes of the decrease in 

 the supply of useful food fishes and of the various factors enter- 

 ing into that problem, in pursuance of these objects has been prose- 

 cuting a detailed inqixiry, embracing deep-sea soundings and 

 dredging, observation of temperatures at different depths, trans- 

 parency, density and chemical composition of sea-water, investi- 

 gation of surface and under currents, etc. ; in other words, mak- 

 ing a complete exploration of the physical, natural and economic 

 features of the sea, besides collecting a large number of specimens 

 of natural history. The expeditions sent out by this Commission 

 have brought to light from the deep beds of the ocean an ex- ' 



