230 



PRESSURE, WINDS AND WEATHER 



Comparison of Theory with Observations. 



The passage of a complete wave over the three stations has now been followed and 

 we have seen how the air is set in motion with a consequent modification of the pressure. 

 This modification has been the most marked at Cape Evaus, less so at Franiheim and has 

 hardly aiiected the Cape Adare pressure at all. The actual pressures are not the sums of 

 the waves and the normal pressures as shown in the left hand diagrams ; but are as shown, 

 at least qualitatively, in the right hand diagrams. Figure 74 has been prepared from the 

 right hand halves of figures 66 to 73 in exactly the same way as the plates in Volume II 



Fig. 71. Modified pressure waves. 



have been prepared from the actual observations. The three upper curves show the actual 

 pressures at Cape Adare, Cape Evans and Framheim, and the lowest curve the pressure differ- 

 ence between Cape Evans and Framheim. By comparing these curves with those in figure 656 

 the modifications due to the air motion are clearly seen, and they have two very important 

 results. 



In the first place they accelerate the arrival of the maximum pressure at Cape Evans. 

 In the case considered, which of course is only qualitative, the maximum pressure arrives 

 at Cape Evaus while the crest of the wave is still over Framheim. On the other hand 

 the mininmm is hardly afiected. This, no doubt, is the explanation of why the maxima 

 appear to travel faster than the minima from Framheim to Cape Evans as found from the 

 actual observations (see table 122). 



In the second place it will be noticed that as soon as the bfizzard commences the pres- 

 sure at Cape Evans commences to rise relatively to Framheim, so that the lower curve of 

 figure 7i is appreciably different from that of figure 656. 



