491 



In Table V. an analysis ig given of the wind observations made on the more lengthy and representative 

 sledge journeys. 



THE DISTRIBUTION OF BAROMETRIC PRESSURE IN RELATION TO WIND. 



The movement of atmospheric air currents as regards both direction and rate is, of course, governed by 

 the distribution of barometric pressure, and in the southern hemisphere an easterly wind implies the 

 existence of an area of relatively high pressure to the southward of the point at which the wind is 

 observed. If, therefore, it could be shown that such an area of high pressure of a more or less permanent 

 character existed over the Great Ice Barrier to the southward of Ross Island, the distribution of wind 

 directions which was observed at the " Discovery's " Winter Quarters would be at once confirmed and 

 explained. 



A consideration of the problem of the general air circulation in the south polar region leads almost 

 irresistibly to the conclusion that some such accumulation of air must take place in its higher latitudes, 

 but unfortunately the data yielded by the expedition are not such as would justify us in saying that its 

 existence is absolutely proved, although perhaps it goes a good way in that direction. 



On most of the sledge journeys readings of aneroid barometers were made and recorded, although in 

 some instances at somewhat irregular intervals. These readings were affected by two distinct causes, 

 the variations in level of the different places of observation, and the changes in pressure due to movements 

 of the atmosphere, and it is difficult to say to what extent these may have severally contributed to bring 

 about the difference in pressure observed between any two consecutive readings. On some journeys, in 

 the neighbourhood of land, the effect due to the first named cause was so great as to render that due to 

 the second quite inconspicuous ; but the journey of Lieutenant ROYDS to the south-east to which reference 

 has already been made was over the level ice quite away from the land, and therefore it seems fair to 

 assume that any changes of level during that journey would be very slight and gradual and not such as 

 would mask the true barometric oscillations. 



The barometric observations made on that journey have therefore been dealt with as follows : The 

 journey out and home was divided into distance-intervals of twenty miles, and all the observations made 

 between and 20, 20-40, 40-60, &c., miles from the ship were meaned and the result compared with the 



Distances from the ship. 



f) 



10 



50 



Outward. 

 20 90 no 



130 



Miles 

 150 170 150 



130 



Homeward . 

 no 90 70 



50 



+ 



Zero 



In. 

 005 



0-15 



0-25 



0-30 



\ 



\ 



\ 



+ 

 Zero 



In. 

 0-05 



o-io 



015 



O-2O 



O-25 



O-30 



Fig. 1. Difference between the mean height of the barometer at Winter Quarters and on the sledge journey to the 



south-east across the Great Ice Barrier. 



3 R 2 



