PREVIOUS CRUISES AND PURPOSES OF CRUISE VII 13 



In some respects conditions of electric study at sea are more 

 favorable than on land and the vessel does not have to be non- 

 magnetic for these investigations. The potential gradient of the 

 atmosphere undergoes daily variations which are simultaneous 

 over the whole Earth, and are thus independent of local time. 

 This important fact had been hidden for years in the data col- 

 lected ashore, because local disturbances of the atmosphere are 

 almost the rule. The phenomenon was apparent when records 

 from all the oceans were compared. 



Important advances may be expected in these subjects when 

 the upper air is investigated, for until now observations have been 

 confined largely to the Earth's surface. In fact, plans for using 

 dirigibles, balloons, and even rockets for this work are now being 

 made. 



We have already made reference to the oceanographic studies 

 made on the Carnegie on her seventh cruise. A brief orientation 

 will make the following narrative more intelligible; although, due 

 to the great number of separate sciences concentrated here, this 

 field of research is even more confusing than magnetism and 

 electricity. 



Aside from its importance to many branches of science, a 

 knowledge of the oceans has a practical value for mankind. The 

 intelligent development of our fishing industries, the laying of 

 oceanic cables, the proper construction of harbor-works, oceanic 

 commerce and navigation, as well as long-range weather fore- 

 casting, are all dependent on an understanding of oceanic con- 

 ditions. 



Changes in the physical properties of sea- water affect profoundly 

 the life of the sea, and have even brought about evolutionary 

 processes through changes of ocean-currents. Physics, chemistry, 

 physical geography, meteorology, astronomy, zoology, botany, 

 bacteriology, and physiology, all play their part in developing 

 a proper picture of the water-world around us. To indicate how 

 large a part of the Earth is covered by the oceans, we might 

 call attention to the fact that a whole hemisphere, with its center 

 near New Zealand, would have only one-tenth of its area as dry 

 land! And the average depth of the seas is over two miles. 



