THEORETICAL PRESSURE DISTRIBUTION. 



219 



There would therefore be an easterly wind over the east of the Barrier and a southerly 

 wind alonii the line of the mountains. It is also clear that the intensity of the southerly wind 



LOW 



SE.A 



BARRIER 



HIGH 



HIGH 



ia) (b) 



Fig. 61. Theoretical pressure distribution, 

 must increase as it flows towards the north because it is constantly receiving air both from 

 the south and from the east of the Barrier. In fact practically the whole of the air set in 

 motion on the Barrier is concentrated in the current which flows across the north-west corner of 

 the Barrier near to Cape Evans. This is shown diagrammatically by the arrows in figure 646. 



Now it does not matter how the motion of air is deflected or restrained the pressure 

 and wind velocity will always adjust themselves in time until (neglecting the effect of friction) 

 the air is travelling along the isobars with the high j^ressure on the left and the low pressure 

 on the right and the distance between the isobars will be inversely proportional to the wind 

 velocity. When the wind flow shown in figure 646 has become established the isobars will 

 have adjusted themselves to be parallel to the flow and near together where the wind is 

 strong. We therefore get a system of isobars like that shown on the same figure. We see 

 that over the east of the Barrier where the air can move from east to west the original 

 isobars are not afiected, but near the Western Moimtains the isobars turn sharply to the 

 north and crowd together near Cape Evans where the air current is strong. Whereas before 

 the air motion started the pressure at Framhoim and Cape Evans was the same, we see 

 from figure 646 that when motion occurs it is necessary to cross two isobars in going from 

 Framheim to Cape Evans, hence the pressure is now appreciably higher at Cape Evans than 

 at Framheim. This increase of pressure is due to the concentration of the air motion over 

 the north-west of the Barrier, but it is brought about in two ways, first the stoppage of the 

 easterly wind over the west of Barrier causes the piling up of the air there and a 

 consequent increase of pressure, also the air moving rapidly from south to north near the 



