PRESSURE WAVES ON THE PLATEAU. 



215 



stations and we notice that the four epochs occurred earlier on the plateau by the following 



amounts : — 



Table 124. 



Neglecting the minimum III, the epoch of which is not clearly marked at any of the 

 stations, we see that the phase on the plateau is about twelve hours ahead of Framheim and 

 twenty-four ahead of Cape Evans. These values can only be approximate for three waves cannot 

 possibly give an accurate mean (they give the difference Cape Evans- Framheim, 12 hours, 

 while the true mean is nine hours), but it is important to know that these well-marked waves 

 as well as several minor ones which have not been discussed here prove that the waves 

 arrive on the Polar Plateau before they affect Framheim and Cape Evans and that they 

 take something like twelve hours to advance from the plateau to Framheim. 



The pressure observations made by Amundsen when on the Polar Plateau have also been 

 examined. The route taken by Amundsen was nothing like so level as that followed by 

 Scott and as he travelled more rapidly I find it impossible to rid his pressure curves from 

 the effect of changing height. It happens, however, that from December 15th to 18th he was 

 at or near the Pole and therefore his height did not vary appreciably during this period. 

 During these days a very small pressure wave passed over the sea-level stations which is 

 clearly shown by the Polar observations, the maximum occurring at 6 a.m. on the 16th 

 at the Pole and fourteen hours later at Framheim. Thus this single wave confirms 

 the results made by Captain Scott's Party. The pressure curve at the Pole during this 

 period has been added on plate 22, Volume II, for comparison with the curves at the sea-level 

 stations. 



Turning now to the observations made on the plateau behind the Western Mountains 

 near to McMurdo Sound which are plotted on plate V, we see that here also there is no 

 doubt that the waves of pressure which affect McMurdo Sound are recognisable on the plateau 

 Unfortunately during this period the pressure waves were less in evidence even than during 

 the Polar journey. There is only one clear point of inflexion, the one recorded on the 23rd 

 November, but from this and a few of the smaller irregularities one can conclude with 

 some certainty that the waves affect the plateau, and the phase is either equal to or 

 slightly behind that at McMurdo Sound. The waves are also slightly smaller than at sea- 

 level. 



We have now shown that the pressure waves can be detected at sea-level in the Ross 

 Sea area and also on the surrounding plateau. They appear first on the Polar Plateau, then 

 about twelve hours later at Framheim, nine hours later at Cape Evans, and finally nine hours 

 later still at Cape Adare. 



If we assume as a first approximation that the waves travel with a linear wave front, 

 these observations are ^iufficient to fix the direction in which they travel. 



