REPORT ON ATMOSPHERIC CIRCULATION. 7 



Temperature of the Air over the Open Sea. — Table II., App. pp. 4-6, which has 

 been constructed similarly to Table I., shows the deviations each two hours from the 

 mean daily temperature of the air as observed on board the Challenger. The 

 following figures show the daily march of the temperature of the air over the North 

 Atlantic on a mean of the same one hundred and twenty-six days for which the 

 temperature of the sea has been given (Plate I. fig. 2) : — 



2 a.m. 

 4 „ 

 6 „ 



The ampbtude of the daily fluctuation is thus 3°"2. In the South Atlantic, about lat. 

 36° S. and long. 36° W., the diurnal range of temperature is 2°'5 ; in the North Pacific, 

 about lat. 37° N. and long. 168° W., 3°-l ; and in the South Pacific, about lat. 36° S. 

 and long. 100° W., 4° - 0. In the neighbourhood of the equator in the Atlantic, about 

 long. 18° "W., the daily range is 2°"6, and in the Pacific, about long. 145 E., 2° - l. Hence 

 while the mean daily range of temperature of the air in the anti-cyclonic regions of the 

 four great oceans is 3°'2, in the neighbourhood of the equator, where the sky is more 

 clouded, it is about a degree less. In high latitudes the daily range is much less, as 

 will appear from the following table : — 



The general result is that the daily range of the temperature of the air on the open 

 sea is from three to four times greater than that of the surface temperature of the sea 

 over which it lies. 



Part of this increased daily range of the temperature of the air as compared with 

 that of the sea was no doubt occasioned by a higher temperature during the day and a 

 lower during the night on the deck of the Challenger as compared with that of the 

 free atmosphere over the sea all round. But, after making allowance for this disturbing 

 influence, it may be assumed that the temperature of the air has a considerably larger 

 daily range than that of the sea on which it rests. The point is one of no little interest 

 in atmospheric physics from its important bearings on the relations of the air and 

 its watery vapour, in its gaseous, liquid, and solid states, and of the particles of dust 

 everywhere present, to solar and terrestrial radiation. 



