306 



POLAR PROBLEMS 



a maximum in the afternoon. The short series of observations at 

 Wandel Island, at Petermann Island, and at Snow Hill Island yielded 

 analogous daily variations. 



It is interesting to note that the curves thus obtained resemble 

 those resulting from the observations of stations in intermediate 

 altitudes in the temperate zone (Berne, for example). 



In the Antarctic the influence of cloudiness on diurnal atmospheric 

 pressure is very clearly evident. In the South Orkneys and at Snow 

 Hill, when the sky was clear, the barometric curve was very regular 

 and comprised a single period having a maximum at about noon and a 

 minimum at about midnight. The amplitude was i millimeter at the 

 South Orkneys and 0.7 millimeter at Snow Hill. 



When the sky was covered the curve was reversed : the maximum 

 occurred at midnight and the minimum at noon. The total amplitude 

 was 0.5 millimeter. 



CASUAL VARIATIONS OF ATMOSPHERIC PRESSURE 



With increasing latitude the casual variations of the pressure 

 become more frequent and stronger. The monthly amplitude, i. e. the 

 difference between the greatest and the smallest figure for pressure 

 in a given month, affords a good criterion of these accidental variations. 

 This monthly amplitude is as follows: 



At Buenos Aires the barometer rarely goes below 740 millimeters. 

 At Tierra del Fuego it often goes down to 720 millimeters. In the 

 Antarctic pressures less than 710 millimeters are observed every year. 

 On the first of April, 1912, at the South Orkneys the pressure at sea 

 level fell to 6q8.2 millimeters. 



Temperature of the Air 



A mean isothermal map of South America shows that between 

 latitudes 22° and 56° the temperature ranges between +24° and +5° 

 C, i. e. decreases by 19° for an increase of latitude of 34°. 



