MAYOR— DETECTING OCEAN CURRENTS. 155 



well, southern Greenland and the Shetland Islands was distinctly 

 lower than that of the air. 



The average COo tension of the air over the ocean seems to be 

 about 0.000295, this being the mean of 51 observations made by 

 Thorpe between Brazil and England. In 1917, however, using ap- 

 paratus given to me by Professor McClendon, I tested the CO. 

 tension of the air over the Pacific between Samoa and San Fran- 

 cisco, but there was apparently no relation between the local CO. 

 tension of the air and that of the water under the air, this lack of 

 coordination being due in all probability to the great mobility and 

 rapid flvictuation in COo tension in the air as compared with that of 

 the water. It would apparently be necessary to obtain several thou- 

 sand determinations of the CO._, tension of air over the ocean taken 

 at all seasons and in all weathers to determine its mean CO. tension 

 with accuracy, but the determinations that have been made indicate 

 that it is not far different from that of the air over the land. My 

 average for three voyages over the Tropical Pacific is : Temperature 

 27.5°, PH 8.22, and COo tension 3.15 ten thousandths of an atmos- 

 phere. Thus the tropical waters appear to have a CO. tension 

 slightly above that of the atmosphere. 



We lack sufificient data for a definite statement as to whether 

 COo is on the whole passing from air to sea or vice versa, but the 

 surmise may seem reasonable that a balance is maintained ; the ab- 

 sorption of COo from the air by the Polar Seas being offset by its 

 passing out of the ocean over the wide area of the tropics, while the 

 temperate regions stand in an intermediate relation, the water ab- 

 sorbing COo during the winter and giving it out to the air during 

 the summer. 



It may be of interest to compare our observations with those of 

 Palitzsch, 191 1, who was the first to apply Sorensen's colorimetric 

 methods to the study of the hydrogen-ion concentration of sea 

 water. 



Palitzsch used naphtholphthalein and phenolphthalein as indica- 

 tors and tested the PH of the Black Sea, Sea of Marmora, Medi- 

 terranean, Atlantic and North Sea in summer with the following 

 results : 



