18 



"Valdivia, " and "Siboga, " among others. The programs of the recent 

 German expedition to the South Atlantic on the "Meteor," and of 

 the exploration of Davis Strait in 1923 by the U.S. Coast Guard 

 cutter "Marion," have, by contrast, been primarily physical and 

 dynamic, recalling the attention devoted to the Chemistry and Physics 

 of the sea water on the cruises of the Challenger and of the Pola 

 and this also applies to the current cruise of the "Carnegie." 



New vieiTpoints, developed of late, have greatly stimulated 

 interest in these questions, at all the centres where oceanographic 

 research is now being actually prosecuted. 



In America, where most of the older oceanographic exploration 

 was sponsored by institutions whose chief interests lay in Biology, 

 the physical side was even more neglected than in Europe, from the 

 days of the "Blake" until the renaissance of Oceanography in this 

 country in the first decade of the present century, described else- 

 where "(Page ). Since then, however. Ocean Physics has been a 

 primary object for the Scripps Institution in California, as well as 

 for the International Ice Patrol operating around the Grand Banks; 

 also for some of the Atlantic cruises of the Biological Board of 

 Canada, of the U.S. Bureau of Fisheries, of the Museum of Oomr- 

 parative Zoology, and of the Carnegie Institution. 



Until recently Physical Oceanography has been confined to the 

 stage of exploration; first, because of the fragmentary state of our 

 knowledge of all the phenomena involved, second, because of any 

 method for calculating quantitatively, from data obtainable in 

 practice, the tendency that internal hydrostatic forces exert to 

 set the water in motion. Until Bjerknes' studies in hydro-d^^Tiamics 

 led to the development of such a quantitative method, it was 

 impossible to analyze the relative importance of the internal 

 dynamics of the water, and of the external forces exerted by the 

 wind, as the causes of ocean currents. In fact, this still remains 

 one of the outstanding problems in Oceanography (Page 37 ). 



At present, the attention of the ocean physicists is chiefly 

 focused at present on the following fields: (1) the distribution of 

 temperature and salinity within the sea, (3) its circulation in 

 detail, (3) the penetration into it of the sun's rays. 



1, Temperature and Salinity 



There is as good reason from the biologic side as from the 

 strictly physical for studying the temperature of the sea, because 

 this, more than any other one feature of the watsr, directly co.itrols 

 the distribution of animal and plant life. Because of the important 

 role of temperature in governing the rates of animal and plant 

 metabolism, on which we have touched elsewhere (Page 53 ) the 

 seasonal changes in the temperature of the water present special 

 problems to the marine biologist in his studies of such events in the 

 life cycles of animals and plants as their breeding periods, the 

 duration of the periods of incubation or of larval life, rate of 

 growth, feeding activity at different seasons, seasonal migrations, 

 and many others. The temperature-optima and the lethal limits need 

 also to be determined at different stages in development for every 



