ANNUAL VARIATION. 



173 



Table 97. 



Normal pressure at Framheim as determined from four years' observations in McMurdo Sound 



and the smoothed differences found in 1911. 



The yearly pressure variation for Framheim given in table 9G and tabic 97 are shown 

 in figure 55c. It will be seen that the variation for the single year, thin curve, has the same 

 general characteristics as the variation obtained from the four years' observations in McMurdo 

 Sound, thick curve, the chief difference being in the high values of the pressure during the 

 months of November, December 1911 and January 1912. Either curve shows that the yearly 

 variation is very similar at both McMurdo Sound and Framheim, but that the latter has the 

 larger amplitude. 



From a physical point of view the moet interesting feature of the pressure relationship 

 between McMurdo Sound and Framheim is that the pressure difference is not that which would 

 be expected from the temjierature relationship. At both t-tations the pressure is least in the 

 coldest months. Further Framheim is colder than McMurdo Sound and its mean pressure 

 is less, also in the months in which the temperature difference between the two stations is 

 the greatest the pressure difference is the greatest. Such a relationship would be impossible 

 if the density of the air only controlled the pressure ; we shall show later that the solution 

 of the apparent paradox is to be found in the motion of the air as constrained by the 

 Western Mountains (see page 238). 



Canpe Adare. 



In addition to the pressure values for Cape Adare given in table 95 further data are 

 available from the observations made in 1899-1900 by the Southern Cross Expedition. For 

 the eleven months, March 1899 to January 1900, we have pressure observations made 

 twice a day, at 9 a.m. and 9 p.m. ; although these are not so good as observations taken 

 more frequently they give values for the mean monthly jwessure which are not far from the 

 true values. 



We have then two separate series of pressure data, the first consisting of eleven monthly 

 values and the second of ten monthly values. It is possible to extend these two series into 

 complete years with a considerable amount of certainty. 



Consider first the second period which commences with March and ends with December 

 1911. From figure 56, page 170, it will be seen that during the period when simultaneous 

 observations were taken at Cape Evans, Cape Adare and Framheim the mean monthly pres- 

 sure at Cape Adare, with one alight exception, lay always between the values for Cape Evans 

 and Framheim. It therefore seems reasonable to conclude that the pressure for January 1912 

 at Cape Adare lay somewhere between the values which wo have for that month at Cape 

 Evans and Framheim. As it happened these values were near together, being 29-43" and 

 29'40" respectively. It is almost certain therefore that the pressure at Cape Adare during 



