LXX PRESIDENTIAL ADDRESS 



and its steam cloud, and it was clear to us then that the part of 

 the atmosphere visible to us, instead of being divisible into three 

 parts, as during calmer weather, now appeared to consist of only 

 two air currents moving rapidly in opposite directions, namely, the 

 south-easterly blizzard, blowing at about 50 to 60 miles an hour 

 during the fiercer gusts; and the poleward-seeking high-level 

 current. It was always noticeable that, as the blizzard developed 

 in intensity, this latter current veered continuously more and more 

 south, until at last it became a north to south wind. 



Another very interesting fact which we noticed during the pro- 

 gress of blizzards was that the high-level wind blowing polewards 

 decended lower and lower as the blizzard progressed, first truncating 

 the top of the steam column of Erebus, and then slicing it off 

 section by section until at last the column was cut off short at the 

 edge of the crater. Later, one could see, by the ripping off of the 

 snow-drifts by this northerly wind, that its lower limit had descended 

 about 1,000 feet below the summit of the volcano. In other words, 

 during the most severe blizzards, the whole of the poleward-seeking 

 system of air streams appeared^ to sink vertically by an amount 

 equal to about 3,000 feet. 



Another feature of interest was that, at the conclusion of the 

 blizzard, while the air had become calm at sea-level, at our winter 

 quarters, at a higher level the air would be moving rapidly north- 

 wards, and in a short time this high-level southerly air stream 

 would spread up to and even over the top of Erebus ; and then the 

 great steam vane, some 20 to 30 miles in length, attached to the 

 top of Erebus, would at once swing around from south through 

 east to north, until little by little the normal plateau wind resumed 

 its old direction from W. by S. to E. by N., and reclaimed control 

 of the Erebus steam vane, forcing it back into an E. by N. 

 direction. 



We now pass on to a most important question of great signifi- 

 cance. In most parts of the world, with the exceptions of the 

 North and South Poles, the barometric pressure is greater in winter 

 than in summer, for as the cold of winter approaches, the air in 

 contact with the cold sea or cold land becomes chilled, and so is 

 rendered denser in winter than in summer; but at the Poles in 

 winter the barometric pressure is lessened. Now, in whichever 

 hemisphere it happens to be winter, it is the experience that in that 



' This sinking does not probably imply that the whole atmosphere during a blizzard is 

 thinned to the extent of 3,000 feet, as, if that were so, the barometer would fall greatly during 

 a blizzard, which is not the case. There may be some actual thinning, but the phenomenon 

 appears to be chit fly due to the high level polar cyclone successively affecting lower strata of 

 he atmosphere during the progress of a blizzard. 



