THE HEIGHT OF THE BARRIER. 



287 



The numbers in this table have been plotted on a curve in figure 86, from which it 

 vviU be seen that the pressure relative to Cape Evans falls to 79° S. and then remains 

 constant to 83° S. 



FlQ. 86. Dillerence of pressure betweeu Cape Evans and positions on the Barrier. 



The first question we have to decide is how much of this pressure difference is due to 

 pressure gradient and how much to difference in height ? 



It is quite impossible from the barometer observations alone to answer this question, but 

 the air motion throws considerable light on the subject. Both the wind observations 

 and the sastrugi show that the prevailing wind over the west of the Barrier is from the 

 south. Thus over this region the isobars must run almost parallel to the track followed 

 by the sledging parties. This leads us to the conclusion that there can be little or no 

 pressure gradient along the track, if there is any change at all it will be a slight increase 

 towards the south. Thus the whole fall of pressure observed must be due to change of 

 height, but there may be a slight additional change of height compensated for by a slight 

 increase of pressure. The latter, however, cannot be determined beyond the fact that it 

 is small and therefore may safely be neglected. We will therefore assume that the whole 

 pressure difference between Cape Evans and the Barrier is due to difference of height ; the 

 height of the Barrier can then be determined from the pressure and temperature observa- 

 tions. The average pressure and temperature on the Barrier during the period over which 

 the observations extend was 29'50" and 15°F. respectively. South of 79° S. the pressure 

 on the Barrier is uniformly ^20" below the pressure at Cape Evans. These data give 170 feet 

 = 52 metres as the mean height for the Barrier south of 79° S. At Corner Camp the 

 pressure is ^09 inches below that at Cape Evans which corresponds to an elevation of 80 feet. 



It is interesting to notice that Mohn calculates from Amundsen's observations that the 

 mean height of the east of the Barrier is 60 metres, it therefore seems very probable that 

 the true height of the Banier is between 50 and 60 metres above sea-level over the greater 

 part of its immense expanse. 



Thus the chief heights along the track from Cape Evans to the Beardinore are :— 

 Cape Evans — Sea-level, 

 Corner Camp — 80 feet. 

 One Ton Camp (79i° S.) to the Beardmore— 170 feet. 



