MAYOR— DETECTING OCEAN CURRENTS. 161 



and this deeper water is in turn replaced by the water which has 

 been temporarily heaped up in front of the gust. There is nothing 

 to prevent an under-water counter current, whereas in order to fill 

 the hollow by surface water the current would have to move against 

 the prevailing wind as at a, Fig. i ; and the friction between air and 



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water is much greater than that between water particle and water 

 particle. Despite this process of local adjustment, however, the 

 westerly trend of the surface current tends to raise the general ocean 

 level in the western regions of the Tropical Atlantic and Pacific, and 

 this is counterbalanced by the great oceanic surface eddies of which 

 the Gulf Stream and the Japan Current are well known examples. 

 The general up-welling of deep water in tropical regions has been 

 known since the cruise of the Challenger. 



Thus due to local causes, water from the depths of the Tropical 

 Pacific sometimes comes to the surface in large quantity, and retains 

 some of its easterly movement, even against the prevailing wind. 

 Then upon being heated by the sun and mixing with the warm sur- 

 face waters its capacity for retaining free CO^ is reduced, and its 

 carbon dioxide passes out into the atmosphere. 



As is well known McEwen, 1910, 1916, etc., has demonstrated 

 from studies of salinity that great quantities of deep water are con- 

 stantly welling up along the Pacific coast of America, and in con- 

 firmation of this fact I find that the COo tension of the surface 

 water along the Pacific coast of the United States is considerably 

 higher than we would expect from its low temperature, and much 



