304 POLAR PROBLEMS 



Between the South Orkneys and Snow Hill, whose latitude is 

 64° 22', the difference in pressure is 0.7 millimeter. The decrease 

 in pressure thus becomes less rapid south of the South Orkneys, 

 inasmuch as here there is one millimeter change for every 3° of latitude. 



The observations at the two adjoining islands, Wandel and Peter- 

 mann, differ much from one another, although they were made almost 

 at the same place. The mean of the two years' observations gives a 

 difference of 2.4 millimeters between the South Orkneys and these 

 stations in a difference of latitude of 4° 20'. 



South of Petermann Island there have been no fixed stations. The 

 only long-series observations are those of the Belgica to the west in 

 Bellingshausen Sea and those of the Deutschland to the east in Weddell 

 Sea. 



The difference between the observations of the Belgica, in an aver- 

 age latitude of 70° 35', and Punta Arenas was -9.2 millimeters in a 

 latitude difference of 17°. Between the South Orkneys and the Belgica 

 the difference in pressure would therefore be only i .4 millimeters for 

 about 10° difference in latitude. The pressure would be about i 

 millimeter higher in latitude 70° in Bellingshausen Sea than at Peter- 

 mann Island in latitude 65°. 



The observations of the Deutschland expedition grouped according 

 to belts of latitude give the following differences with the atmospheric 

 pressure at the South Orkneys: 



6o°-65° -2.8 millimeters 



65°-70° -3-9 



7o°-75° -2.8 



S. of 75° -1-3-0 " * 



* Two months of observation in summer. 



These results do not clearly prove that pressure increases with 

 increasing nearness to the south pole, in other words that there exists 

 an Antarctic anticyclone, but they prove in any case — in so far as one 

 may draw conclusions from a relatively restricted number of observa- 

 tions — that the atmospheric pressure which decreases about i milli- 

 meter per degree of latitude down to the 60th parallel decreases much 

 more slowly farther south and probably increases beyond the 70th 

 parallel. 



ANNUAL VARIATION OF ATMOSPHERIC PRESSURE 



The annual march of atmospheric pressure over the southern part 

 of South America differs according to the elevation and the latitude 

 of the observing station. 



In latitude 35° (Buenos Aires) the annual curve shows a minimum 

 in December-January (summer) and a maximum in June-July (winter). 

 The mean annual amplitude is 7 millimeters. 



