DE1-P-S1'.\ I-XI'I.OKATION 



Lecture delivered in the United States Nationcl Muscnni, April 22, iSS^. !>>' 

 I'rof. Wm. H. Dali.. 



Ladies and Gkntlemkn: 



The siibjoi't of tliis Icetuic may be defined as covering the 

 investigation of all that relates to the ocean and its inhabi- 

 . tants, considered as a wliole, with the exception of those 

 features which are due to the influence of external causes, 

 such as the tides, and those which are exhibited solely in 

 shallow water, and therefore are in one sense characteristic 

 rather of the coasts themselves than of the sea. 



The field naturally divides itself into two areas of re- 

 search, the ]>hysical and the biological. The physical fea- 

 tures inelude the temperature of the sea-water in different 

 geographical regions and at different depths ; the compoHition 

 of the water and investigations into the relative amounts of 

 mineral .salts, organic impurities, air, or other gases contained 

 in it, and upon which its weight or density depends; the 

 motions of the water contained in the bed of the ocean, 

 whieh, apart from the tides, dei)cnd largely on its variations 

 in temi)crature and density, and which, when tolerably con- 

 stant and sufficiently well marked to attract the attention of 

 navigators, are commonly known as ocean currents; and, 

 lastly, of the deptJi of the sea or the topogra])hy and physi- 

 cal features of the bed in which it is contained. 



The biological features include the capture and classilica- 

 tion of the animals living in the sea, especially on its bottom, 

 and the circumstances attending their existence there, both 

 as regards their food and manner of living, and the results, 

 if any, produced by the presence of their r.'inniiK .ifttr 

 death. • 



It is evident that the field is too large to be treated in 

 detail within the limits of a single lecture, and therefore I 

 shall conline myself to a general <lescription of the means 

 used in exploring the bed of the ocean, of the conclusions 

 whicli ai)j>ear to be warranted by the discoveries so far 



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