PRESIDENTIAL ADDRESS. LXIX 



by the steam column from the eruptions just described, the great 

 current of poleward-seeking air was reached, and this extended 

 upwards to vast heights, probably of the order of at least 25,0(k 

 feet. 



If these conclusions are correct for the Mount Erebus region, 

 the high level plateau wind, which may there be considered the 

 abnormal anti-cyclone, locally deflected eastwards into Ross Sea, 

 is thus no less than 15,000 feet in altitude at its upper limit, that 

 is over 4,500 meters instead of Meinardus' estimate of 2,000 

 meters. This does not invalidate Meinardus' conclusions in regard 

 to the upward limit of the normal anti-cyclone, such as that of 

 Kaiser Wilhelm II. Land. At Erebus, there are two abnormal 

 conditions afiPecting the height of the anti-cyclone — (1) tlie upward 

 deflection of the normal anti-cyclone by the Antarctic Horst ; (2) the 

 upward deflection due to the high volcanic cone of Erebus. ^ 



A feature of great interest in the atmospheric circulation of the 

 Antarctic revealed itself to us at the time of the coming on and 

 development of the great blizzards. We were able to distinguish 

 between high-level blizzards and low-level blizzards, the former often 

 blowing hard at a level of 6,000 feet about over our heads, while 

 below all was calm. A premonitory symptom, especially in winter 

 time, of the coming on of an impending blizzard was the swinging 

 around of the great rolls of alto-cumulus clouds from a N.-W. 

 and S.-E. to a N. and S. direction. Meanwhile, the summit of 

 Mount Discovery, over 60 miles to the S.S.W., would be capped 

 with cloud. Later, after an interval of perhaps a few hours, and 

 usually, but not always with a low barometer, a heavy roll of a 

 dense low-lying cloud, something like the roll that precedes the 

 southerlies along our Australian coasts, would be seen in the south. 

 This rushed upon us at such a rapid rate that, even when only a 

 half-a-mile distant from our winter quarters, we had only just 

 time to run for shelter before the full fury of the blast struck us. 

 It was difficult to see, as the blizzard progressed, exactly what was 

 happening in the atmospheric circulation at the higher levels, on 

 account of the denseness of the drift snow. By continuous careful 

 observing, we occasionally caught glimpses of the top of Erebus 



' On our journey in 1908-9 to the edge of tlie South Magnetic Pole area we observed that 

 for the last 50 miles of our march before reaching lat. Vi" 25' S., long. 155° 16' E., the chief 

 sastrugi trend from due S. to N. Thus the normal anticyclone wind blows there first from S. 

 then backs to the S.E., leaving wsak^r broad-topped " ramp " sastrugi trending from S.E. to N.W. 

 Recently, sinc3 this address was read, the returning mmbsrs of Dr. Mawson's Au5tralaslan 

 Antarctic Expedition report that at Adfilie Land, and for 300 miles to the S.E. of Dr. Mawson's 

 base th^re, at the h^ad of Commiawialth Bay, the chii^f sastrugi trend nearly due S. and N., 

 c.ossed by small ir " ramp" saUrugl trending from about S.E. to X.W. The average speed of 

 thi wind throughout th"? year 1912 at Ad6!ie Land was no less than 48 miles per hour. This S. 

 to N. direction inclining towards the coast into a direction a little E. of S. and W. of N. may be 

 looked upon as probably the normil one for the Antarctic anticyclone. 



