4 THE WEALTH OF THE SEA 



whaling vessels are excellent navigators, for they 

 are more familiar with the coastal waters than any 

 one else. 



Oceanography and navigation are sciences which 

 go hand in hand in the development of both fishing 

 fleets and navies. Since the location and extent of 

 the fisheries are controlled largely by the tempera- 

 ture, depth, salinity, purity, and amount of plankton 

 (minute organisms which float with the currents) 

 I of the waters, brief mention of these factors will be 

 made in this section. Their consideration will be 

 worth the while of any one interested in the fisheries. 

 Such a survey will also give much information con- 

 cerning the various forms of marine life and the 

 conditions under which it exists. 



The early Greeks and Phenicians laid the founda- 

 tions of oceanography. In the fourth century b.c, 

 the astronomer Pytheas sailed from the Mediter- 

 ranean to the North Sea and made notable 

 contributions to the oceanography of the Atlantic 

 Ocean and the North Sea. He learned how to deter- 

 mine latitude and discovered that the tides were 

 caused by the moon. 



Later, in the first century B.C., the Greek geog- 

 rapher Strabo made the first deep-sea soundings, 

 measuring depths down to 1000 fathoms. Pliny, in 

 his "Historia Naturalis," recorded 176 marine ani- 

 mals, and was well pleased with his catalogue, as he 

 believed that he had listed all the important marine 

 species. 



Ptolemy, who lived in the second century a.d., 

 prepared a map indicating that eastern Asia came 



