THE HEIGHT OF THE ANTARCTIC CONTINENT. 299 



From this table it will be seen that out of the nine sets of observations seven show 

 an excess of pressui'e in January when smoothed values are considered and six when the 

 actual values are considered. 



The stations have been divided into two groups, one containing the stations in the Ross 

 Sea area and the other the remainder. The latter are all situated on the northern edge of 

 the continent and within a few miles of the open Southern Ocean. With the exception of 

 Cape Adare, the stations in the Ross Sea area are much further south than the remaining 

 stations. 



Now from these observations it is necessary to decide what is the difference of pressure 

 between January and July over the whole region within the Antarctic Circle. Personally I 

 feel that the data are far too few to give anything like the required information, but we 

 can obtain some conclusion to compared with the one used by Meinardus in his calcula- 

 tion. 



Baschin has found that over the Southern Ocean between 50° and 60° S. latitude the 

 pressure difierenc3 January-July is — 0'73 mm., and this result may be accepted with consi- 

 derable confidence. From fewer observations he determines the mean difference within 60° 

 and 66^° S. (the Polar Circle) to be zero. The group of stations on the edge of the Antarctic 

 Continent as shown in the above table have a mean difference of 4-0'58. This indicates 

 that the difference is changing from negative values over the Southern Ocean to positive values 

 over the Antarctic Continent. It is therefore significant that the three most southerly stations all 

 show a high positive value for the difference. Unfortunately these three stations are all in the Ross 

 Sea area and therefore it may be argued that the positive values are local and are due to 

 the Ross Sea and do not really represeiit tne conditions in high latitudes. 



In this connexion the observations at Framheim are of great importance. Meteorologically 

 Framheim is more under the influence of the Antarctic Continent than any other station, 

 as is seen from its low temperature and absence of wind. The observations in July 1911 

 and January 1912 show a difference of pressure for January-July of +12-5 mm., which is 

 by far the largest pressure difference between these two months recorded anywhere in the 

 Antarctic. Taken alone this great difference — larger than the 11 mm. required by Meinardus — 

 might be considered to be accidental and no doubt to some extent it is. We have remarked 

 above * that the difference in pressure between two stations undergoes much smaller changes 

 than the actual pressure itself, and further we concluded that the yearly march of the pres- 

 sure difference between Cape Evans and Framheim shown in figure 57, page 172, was so 

 regular that it probably represents very nearly the true normal difference of pressure between 

 these two stations. By applying these differences to the normal pressure of McMurdo Sound 

 based on four years' observations we found that the normal pressure at Framheim in January 

 and July is 7450 and 735- 6 mm. respectively (see table 97, page 173). This gives a probable 

 normal difference of pressure January- July at Framheim of 9-4 mm. as compared with 5-15 mm. 

 in McMurdo Sound. If such large and similar variations exist between coast and con- 

 tinental stations elsewhere, it shows the futility of attempting to determine even approximately 

 the average pressure difference between January and July for the whole Antarctic from the 

 few available observations, all of which have been made at coast stations. 



As the considerations we have just been discussing are difficult to apply I see no other 

 way to treat the observations available than to take their arithmetic mean. It must not be 



* Page 172. 



