496 



The two sots of observations of the drift of Mount Erebus smoke give slightly different percentages for 

 each of the eight points, but the general agreement between them is surprisingly close considering the 

 conditions under which they were made. Taking the mean of the two sets, we find that at the level of 

 from 13,000 to 14,000 feet the change in the direction of movement of the air currents, which is indicated 

 by the lower clouds, has become further developed, and that, at that height, the easterly current of the surface 

 has become almost entirely superseded by another from between south-west and west. These two directions 

 together account for no less than 64 per cent, of all the observations, south-west alone having 36 per cent. 

 South has 12 per cent., north-east has only 2 per cent., and north and east have each but 4 per cent. At 

 this level, therefore, the dominant air current is unmistakably from between south-west and west, and winds 

 from between east and north, the quarter from which the surface winds chiefly came, are comparatively 

 rare. 



At the level of the upper clouds we find this progressive change in direction towards the westward 

 carried still further, and a marked prevalence of north-westerly winds is shown for the first time. South- 

 west, it is true, still remains the slightly dominant direction, but this may possibly be due to the inclusion 



SURFACE 



W/NDS. 



LOWE 7? 



CLOUDS. 



UPPER 



CLOUDS. 



SMOKE. 



20% 



Fig. 2. Distribution of air currents at various levels. 



