244 PRESSURE, WINDS AND WEATHER. 



From the first line of tlie tabic we see that a cyclone travelling from west to east 

 at 9' 5° of longitude a day with its centre 6° of latitude to the north of the station 

 and causing a fall and rise of the barometer of half an inch in one day would produce a 

 mnd velocity of 251 miles an hour, and the wind direction would change 35° between the 

 commencement and ending of the change of half an inch in the pressure. Now Beaufort 

 force 12 was never recorded at the Gauss Station, hence the cases which give the wind force 

 as 12 or over have to be excluded. This leaves us with one case in the first group, two 

 cases in the second, and three in the third. It will be noticed that the change in the wind 

 direction in these six remaining cases is always above 100°. In other words no cj^clone 

 travelliHg with the given velocity could cause a fall and rise of the barometer of half an inch 

 in less than three days without the wind changing direction at the station by more than 100°. 



The impossibility of Lockyer's cyclones which have their centres 6° to the north of the 

 Gauss Station producing the observed effect is particularly obvious. For such a cyclone to 

 produce a fall and rise of half an inch at the Gauss Station, even in three days, would 

 necessitate a hurricane wind and a change of direction of 88° there, so what the conditions 

 would be nearer the centre can best be left to the imagination. 



The case is not improved by considering other rates of travel or other shapes of isobars, 

 for a little consideration will show that any change which decreases the angle through which 

 the wind should change will increase the wind strength. Thus any wind change of less than 

 100° would always be accompanied by hurricane winds. 



Thus at the latitude of the Gauss Station, no cyclone, no matter what its rate of travel 

 or distance of its centre from the station, could produce a fall and rise of the barometer of 

 half an inch in three days or less without either changing the wnd direction by more than 

 100° as it passed, or causing winds of more than hurricane force. 



Now at the Gauss Station we see barometer changes of much more than half an inch 

 in C3usidei-ebly less thin three days without anij appreciable change of wind direction and the 

 only conclusion to be drawn is that these pressure changes are not produced by moving 

 cyclones. 



There seems no alternative but to assume that the Gauss Station is subjected to travelling 

 pressure waves similar to those in the Ross Sea area. If such waves travel outwards from 

 the continent in all directions their wave fronts will be approximately parallel to the coast. 

 Now along the coast there must ba a steep barometric gradient similar to the one between 

 the Barrier and the Ross Sea and the waves will modify this pressure, increasing and de- 

 creasing it. Thus we see that the pressure waves will increase and decrease the gradient 

 and with it the wind velocity, but as the isobars and wave fronts are parallel there will 

 be little change in the wind direction. 



Just as we found it impossible to say a priori what relationship should exist between 

 the pressure waves at Cape Evans and the wind changes there, so it is impossible to say 

 whether at the Gauss Station the easterly winds should be stronger or weaker with high 

 or low barometer or should increase or decrease with rising and falling pressure. 



It is very significant that at the Gauss Station the wind frequently changed direction 

 suddenly from east to west, and next to the nearly constant winds from the east, winds from 

 the west had the greatest frequency. This would be the natural consequence of pressure 

 waves, but cannot be explained by cyclones unless one makes the impossible assumption that 

 the centres of the cyclones passed frequently exactly over the station when travelling from 

 north to south or from south to north and never passed over the station when travelling 

 from west to east. 



