■210 PRESSURE, WINDS AND WEATHER. 



Pressure Waves and Pressure Distribution. 



From 1st April to the end of December 1911 observations of pressure and wind are 

 available at Framheim, Cape Evans and Cape Adare. These stations are sufficiently near one 

 another to make it possible for us to detect the same series of pressure changes at each 

 station, and we can therefore investigate in what way the pressure variations are handed 

 from station to station and what changes of wind accompany the changes of pressure. 



Two methods of investigation have been found to be of great use in the study : 



(a) A series of sheets was prepared each showing the pressure curves during twelve 

 days for the stations under investigation, the vnnA directions being shown by 

 arrows attached to the curves. 

 (6) The pressure and wind observations were entered on to maps and an attempt made 

 to draw isobars to fit them. 

 The curves and maps will be found in Volume II and the reader will find it necessary to 

 have this volume at hand when reading the present section. It will frequently be necessary 

 to compare the various maps \\-ith the corresponding barometer curves, the plates have there- 

 fore been so bound that each can be unfolded and exposed to view when the book is open 

 at the corresponding map. 



At first we shall discuss only the plates showing the pressure curves and it will be found 

 convenient at this point to unfold all the plates so that they can be rapidly turned over 

 in succession. 



The plates. — On each plate there are six curves which represent 



(1) The barometer and wdnd at Melbourne in Australia 



(2) „ ,, ,, ,, the Bluff in New Zealand 



(3) „ „ „ „ Cape Adare 



(4) „ „ „ „ Cape Evans 



(5) „ ,, „ „ Framheim 



(6) The pressure difference between Cape Evans and Framheim, on this curve the winds 



at Cape Evans have been repeated. 



It will be noticed that the first five curves are arranged according to latitude, Melbourne 

 the most northerly being at the top and Framheim the most southerly at the bottom. 



The curves are plotted to simultaneous time. The arrows are drawn to fly with the 

 wind and the number of feathers indicates the strength of the wind according to the Beaufort 

 Scale. 



The two upper curves will not be considered at present, but we will fix our attention on 

 the curves for the three Antarctic stations— Cape Adare, Cape Evans and Framheim. A cursory 

 glance through the plates vnW show at once that the pressure changes at these three stations 

 are very similar, a succession of waves of various length and depth affecting all three stations 

 in a very similar way. An excellent example is contained in plate 5. A large wave of 

 pressure having a minimum on May 24th and maximum on the 27th or 28th affected all 

 three stations. It will be noticed further that the wave affected first Framheim, then Cape 

 Evans and finally Cape Adare. Framheim is slightly to the south and 400 miles to the east 

 of Cape Evans, and Cape Evans is slightly to the west and 400 miles south of Cape Adare. 

 It is therefore obvious that the pressure system which gave rise to this wave moved from 

 east to west and from south to north, which is the exact opposite of what we should have 

 expected if these waves are due to depressions moving in a south-easterly direction from the 

 Southern Ocean into the Ross Sea. This is not an isolated case, for it will be seen that in 



