70 Hydrogen-ion Concentration arid Electrical Conductivity 



westerly surface drift to the northward or to the southward. More- 

 over, the Ph of this easterly-moving water ought generally to be lower 

 than that of the westerly drift, for the cold waters of the depths arc 

 richer in CO2 than is the warm surface layer. Our observations 

 indicate that this is probably the case; the results upon the eight 

 voyages across the region in the mid-Pacific from 6*^ N. to 2° S. are 



shown in table 4. 



Table 4. 



A low Ph when the current is easterly is, however, not always 

 observed. Thus, on August 1, 1920, the ship ran out of the prevailing 

 westerly drift at about 8 a. m. and was in a strong easterly current 

 until about 4 a. m. August 2, and yet the Ph of this easterly current 

 was exactly the same as that of the westerly drift to the north or the 

 south of it. Naturally, if deep water rich in CO2 comes to the surface, 

 it soon becomes warmed, and thus its excess of carbon dioxide is 

 discharged into the air until the CO2 tension of the water is about in 

 balance with that of the air; and after this process is completed it 

 might, due to momentum, still retain some of its easterly movement, 

 but its Ph would be the same as that of the prevailing westerly surface 

 drift. It seems probable, therefore, that in cases where we find an 

 easterly drift in the mid-Pacific in about 5° N. latitude, and its Ph 

 is about 8.23, it has been for so long a time on the surface that it has 

 attained the temperature and Ph characteristic of the westerly 

 surface drift. 



If these easterly drifts be derived from deep water which has up- 

 welled to the surface, their average CO2 tension ought to be higher 

 than when the current is moving in a westerly direction, and averaging 

 the calculated CO2 tensions of the water between about 6° N. lati- 

 tude and 2° S. latitude, observed on our eight voyages across this 

 region in the mid-Pacific, we find that this seems to be the case, as 

 appears in table 5. 



It seems, then, that the CO2 tension of the surf ace water in these 

 easterly counter currents is appreciably higher than in that of the 

 prevailing westerly surface drift. The atmospheric CO2 has a tension 

 of about 0.0003 of an atmosphere, and thus it appears that these 

 easterly currents probably discharge CO2 into the air. In this con- 

 nection it may be of interest to observe that L. R. Gary (1917) found 

 that the oxygen content of these easterly currents was higher than 

 that of the westerly drift. 



