CHAPTER LVIII. 



UK KNOWLEDGE OF TTTE EARTH AND SEA— HOW IT HAS INCREASED — THE EARTH 13F 

 DAUGHTER OF THE OCEAN— THE OPINION OF SCIENCE— THE MEAN DEPTH OF THE 

 OCEAN— THE EXTENT OF THE OCEAN — ITS VOLUME — SPECIFIC GRAVITY OF SEA-Wi TEB 



—CONSTITUTION OF SALT-WATER — THE SILVER IN THE SEA — THE WAVES OF TiTE 



SEA — THE CURRENTS OF THE OCEAN— THE TIDES — THE AQUARIUM — THE COMMERCE OF 



MOOliRN TIMES— THE SPREAD OF PEACE. 



In the preceding pages the facts have been given in a com- 

 prehensive though succinct form, which enable us to see how, 

 step by step, each one of which became possible only when 

 those preceding had been taken. Mankind has gained a knowl- 

 edge of the outlines of the sea; of the form of the earth itself; 

 of the relative positions occupied by the water and the land ; 

 of their action upon each other, and thus the way has been pre- 

 pared by the enterprize of preceding generations for the scien- 

 tific methods of study which characterize the modern era. The 

 adventurous voyagers of the early times, who, daring as they 

 were, hardly were bold enough to venture in their open boats, 

 propelled only by oars, out of the sight of land, could not bo 

 expected to conceive that it could be possible for men, like 

 themselves, to ever become able to construct ships such as modern 

 nations construct, in which, propelled by steam, voyages should 

 be taken across oceans, and out of sight of land, theiy course 

 over the trackless waters be guided with accuracy and certainty, 

 to any desired point, by the compass and the observations of 

 the motions of the stars. 



By experiment and observation the entire aspect and concep- 

 tion of the ocean has been changed in modern times from that 

 which prevailed in antiquity, or even more recently, until 

 within the few past generations. Though much has been done, 

 in the study of the ocean, toward obtaining a proper conception 



of its influence in the general economy of the globe, j*et there 

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