COMPARISON OF THEORY WITH OBSERVATIONS. 235 



on the plate that during the whole of the 18th the pressure at Cape Evans was slightly 

 rising relatively to Framheim. This has been explained as due to the piUng up of air over 

 the west of the Barrier along the Western Mountains. At 8 a.m. on the 19th a blizzard 

 has started at Cape Evans and now v\ath the increased motion the pressure difference 

 between the west and east of the Barrier rapidly increases, and the pressure difference 

 Cape Evans - Framheim rises by nearly half an inch. 



Another important and interesting example is the blizzard which commenced at midnight 

 of November 15th. At 8 a.m. on November 15th a very shallow low pressm-e area appears 

 over the south of the Barrier. During the day this disappears and by the evening it is 

 replaced by a high pressure area. Although the wind at Framheim is from the south-east, 

 it is almost certain that it is from the east over the greater part of the north of the 

 Barrier. The pressure now rises in the west relative to the east and by the next morning 

 typical blizzard winds are reported from all parts of the Barrier. It is interesting to notice 

 that there has been practically no change in the height of the barometer at any of the 

 five stations between 8 p.m. on the 15th and 8 a.m. on the 16th and yet there is a very 

 large change in the wind conditions which has resulted in a new distribution of the isobars. 

 Similar large changes in wind conditions with little, if any, change in pressure are quite 

 common and many examples will be found if the maps are examined in detail. 



In drawing the maps many interesting facts attracted one's attention, but it would not 

 be wise to discuss the maps in detail as one feels that it is very questionable whether the 

 run of the isobars is anything more than a rough approximation to the actual conditions. 

 There can, however, be little doubt that the general pressure distribution and the sequence of 

 pressure changes is that shown by the maps. 



One point, however, must be discussed before we review our conclusions. We have repeated- 

 ly shown that the consequence of the flow of air from the east to the west of the Barrier, 

 when its motion is stopped and the air is forced by the Western Mountains to flow north- 

 wards, is a rise of pressure at Cape Evans relative to Framlieim. 



We have just examined two cases of blizzards which were accompanied by these relative 

 changes of pressure in the absence of pressure waves, and we found that the pressure differ- 

 ence Cape Evans - Framheim was nearly as large as in the case of blizzards accompanying 

 large pressure waves. The question at once arises may not the bUzzards be the cause of 

 the pressure waves and not the pressure waves the cause of blizzards ? A study of the 

 curves on the plates will soon dispose of this idea. On plate 17 there is a large pressure 

 wave with its crest at Framheim and Cape Evans on the 14th. There was a short blizzard 

 just before, and a longer one just after, the crest passed Cape Evans. Now it will be 

 noticed that both these blizzards were accompanied by a rise in the difference curve although 

 the absolute pressure at both Cape Evans and Framheim was rising throughout one blizzard 

 and falling throughout the other. In this case the pressure wave affected Cape Evans and 

 Framheim almost simultaneously, therefore for practical purposes the pressure wave did not 

 affect the pressure distribution. The blizzards occurred exactly as they would have done if 

 the pressure curve had been a straight line, and the pressure differences shown on the lowest 

 curve were due to the blizzard. 



The way that the induced pressure difference is impressed on the pressure wave is clearly 

 seen in the case of the second blizzard, for the fall of pressure is decreased at Cape Evans 

 and increased at Framheim. In this case it is obvious that the pressure difference is due 

 to the blizzard and is superposed upon the pressure wave. It is therefore clear that the 

 large pressure wave itself cannot be due to the blizzard. 



Granted that pressure waves exist independently of blizzards the fact that they arrive 

 at Framheim before Cape Evans and at Cape Evans before Cape Adare proves that they 



