188 



PRESSURE. 



Table 108. 

 Pressure waves in the Ross Sea area. April to December 1911. 



During the mis.sing months the waves are longer and not so deep as during the rest 

 of the year, therefore the above results are dificrent from what would have been obtained 

 if a complete year's observations were available. It is reasonable to suppose that by applying 

 the factor necessary to convert the above values for Cape Evans to the mean value found 

 for four years to the data for the other stations an approximate yearly mean wdll be found. 

 Thus in McMurdo Sound the mean length of the waves for the four years was 152 hours, 

 while during the period considered in table 108 it was only 142, hence the factor necessary 

 to convert the mean for the broken period into the four-yearly mean is ^/ Similarly the 



factor for converting the amplitude of the waves is 



.572. 



6U5 



Ajiplying the same factors to the 



observations at Cape Adare and Framheim we obtain the mean yearly values given 

 table 109. 



m 



Comparison of pressure ivaves at Antarctic stations.— In table 109 the mean length 

 of the waves, the mean pressure variation in the waves and the mean hourly change are 

 given for eight stations in or near the Antarctic. 



Table 109. 

 Pressure waves greater than -2 inch (5 m.m.) in the Antarctic (yearly average). 



In this table the stations are arranged in order of latitude and three important results 

 are at once apparent : — • 



(a) The length of the waves increases steadily as the latitude increases. 

 (6) The amplitude of the waves is nearly constant. 



