236 



PRESSURE, WINDS AND WEATHER. 



travel. If they travel they must cause pressure diSerence between the stations. We have 

 therefore two causes at work producing pressure difierence between Cape Evans and Framheini, 

 first the passage of the pressure waves and second the dynamical effects of the blizzards. 

 On account of the coincidence that the line joining Cape Evans and Framheim is at right- 

 angles to the Western Mountains and at the same time cuts the wave fronts at an angle 

 of 45°, the two causes increase the pressure diSerence at the same time. Some pressure waves 

 do not produce blizzards, the difference curve in this case is due to the travelling wave alone, 

 examples are seen on May 22 and 23, June 27 to 29, July 30 to August 1, etc. We have 

 just discussed a typical case, in which changes of pressure due to the blizzards are super- 

 posed on the pressure waves and we have examined several cases of pressure difierences 

 produced by blizzards in the total absence of pressure waves. Thus there are examples of 

 all the possible effects to be expected according to the theory. 



To these considerations we also have to add the fact that the pressure waves are recog- 

 nisable on the surrounding plateau and appear on the Polar Plateau before they reach the 

 Barrier, hence the waves cannot be caused by the blizzards. There is no escape from the 

 conclusion that the pressure waves are imposed on the Ross Sea area from outside. 



During the study of the records, which led finally to the theory sketched above, a large 

 number of statistical investigations was made to find the relationship of the pressure condi- 

 tions and changes at the three stations which accompanied the blizzards, northerly winds and 

 calms at Cape Evans. The results of these investigations are contained in table 128. Six 

 classes of wind were taken, five of which are shown in the table ; the class of wind 6 to 

 10 miles an hour has been left out because it adds nothing to the discussion. 



Table 128. 

 Pressure and Winds. 



