152 CARNEGIE INSTITUTION OF WASHINGTON. 



streams during the phenomenal drought of 1918 were all slightly acid, 

 due to carbon dioxide; but the water from the most acid of these springs 

 became alkaline after falling over a cataract only 15 feet in height, 

 and all of the Samoan streams appear to be alkaline in their lower 

 ranges near the sea. 



Daily determinations were made at noon of the hydrogen-ion con- 

 centration of the surface water of the ocean during the voyages from 

 San Francisco to Samoa, Samoa to Fiji, and Fiji to Victoria, British 

 Columbia; and, as in 1917, the results indicate that in the tropical 

 region of the mid-Pacific a sudden change toward acidity usually 

 indicates the presence of a surface current moving toward the east in 

 opposition to the prevailing westerly surface-set. The rapidity with 

 which this test can be made may be serviceable to navigation by indi- 

 cating the presence of an easterly set even before the vessel has become 

 deflected from its true course. 



Tests of the surface waters were also made in the Atlantic on the 

 voyage to and from Trinidad, British West Indies, and between New 

 York and Key West, and these show that the Gulf Stream and tropical 

 Atlantic waters are much more alkaline than the water which drifts 

 down close to the east coast of North America from the Gulf of St. 

 Lawrence to Cape Canaveral, Florida. The test of alkalinity is thus 

 a valuable guide in this region to warn navigators who may be 

 approaching the coast that they are on the inner side of the Gulf 

 Stream, or in proceeding outward that they have reached the surface 

 current of tropical origin. 



The cold arctic water, or that from the depths of the ocean, is more 

 heavily charged with carbon dioxide than is the warm surface drift 

 of tropical origin, and even when the temperature of the waters 

 derived from the depths, or from cold regions, has become practically 

 the same as that of the surrounding water of tropical origin, its carbon- 

 dioxide concentration still remains relatively high, thus causing it 

 to maintain some of its relative acidity. 



This suggests that easterly sets in the tropical regions of the mid- 

 Pacific and Atlantic may be due to water of deep origin coming to the 

 surface. Possibly there is a general easterly movement of the deep 

 water of the tropics to counterbalance the prevaihng westerly set of 

 the surface; but the test of this hypothesis awaits confirmation. 



The growth-rate of the Pacific corals being about twice as rapid as 

 that of corresponding genera in the Atlantic, it becomes evident that 

 the present reefs might readily have attained to their present dimen- 

 sions during the past 30,000 years, or since the last Glacial Epoch. 

 Possibly the fact that the Pacific corals grow more rapidly than do 

 those of the Atlantic may be correlated with the condition that in 

 the Atlantic the corals grow chiefly on the outer edges of wide, shallow 

 flats covered with limestone mud, which when agitated fill the water 

 of the flats with a milky mass of calcium carbonate fatal to pelagic 



