HYDROGRAPHY 167 



The marine biologists of the Carnegie Institute at Washing- 

 ton have made some recent contributions to the subject by 

 taking observations on the alkahnity of the open sea (deter- 

 mined by hydrogen-ion concentration), during which they 

 found in tropical mid-Pacific a sudden change to acidity in 

 a current running eastwards. Now in the Atlantic, the Gulf 

 Stream and tropical Atlantic waters generally are much 

 more alkaline than the colder coastal water running south 

 from the GuK of St. Lawrence. That is, the colder Arctic 

 water has more carbon dioxide. This suggests that the 

 Pacific easterly set may be due to deeper water containing 

 more carbon dioxide (= acidity), coming to the surface at 

 that point. The alkalinity of the sea-water can be deter- 

 mined rapidly by mixing the sample with a few drops of an 

 indicator and observing the change of colour ; and this 

 method of detecting ocean currents by observing the 

 hydrogen-ion concentration of the water might be useful 

 to navigators as showing the time of entrance to a known 

 current. 



Other Physical Characters. 



The phenomena of tides, due primarily to astronomical 

 causes, the formation of waves, the presence and movements 

 of seiches (tidal, temperature, etc.), and the circulation of 

 the atmosphere and other meteorological changes, although 

 aU of some oceanographic importance, need not be dealt 

 with in this outline of hydrography. To discuss all these 

 subjects adequately would require far more space than is 

 available in the present book. 



Some Effects upon Life in the Sea. 



I may conclude this chapter with a brief statement as 

 to the bearing of some of these physical characters of the sea 

 upon the distribution and habits of some living organisms. 



1. Depth is a prime factor in the distribution of marine 

 plants and animals. There are httoral, shallow-water, and 



