LXVI PRESIDENTIAL ADDRESS, 



following giving us an indication of the circulation of the upper 

 atmosphere : — At the great eruption of Mount Pelee, in Martin- 

 que and La Soufriere, in St. Vincent, in the year 1902, vast quan- 

 tities of volcanic dust were projected to heights of over 20,000 feet 

 into the higher atmosphere. The trade wind current is there no 

 more than about 13,000 feet in thickness, so that above that level 

 the dust entered the great stream of the anti-trade wind, blowing 

 from south-west to north-east, in that part of the world. This 

 dust was later identified on the surface of the snows of the Swiss 

 Alps, in Canton Lucerne, and it is thought to have been traced as 

 far as Hamburg, in Germany. This proves that the anti-trade 

 wind does not cease at the northern belt of high pressure, but 

 moves poleward, perhaps as far as Hamburg. Further observa- 

 tions in the northern hemisphere, by means of nepho- 

 scopes, hallons de sonde, &c., prove that there is a 

 steady drift "taking place of the cirrus clouds in the 

 higher atmosphere, from southwards, or west-south-west, towards 

 north-east, or east-north-east. These poleward-flowing high-level 

 air currents from the high-pressure belts form a stupendous whirl, 

 or aerial malstrom, over the north polar area. In the same area 

 the surface winds are westerlies, blowing spirally polewards. Thus 

 we see that two immense air currents, in the northern hemisphere, 

 spiral inwards towards the north pole. Unless there were some 

 kind of counter-current, obviously there would very soon be an 

 intense congestion of air at the north pole, and equatorial regions 

 would be robbed of their atmosphere. There must, therefore, be 

 some great counter-currents which restore the air from the pole to 

 the equator. How this restoration is accomplished is certainly 

 a great crux of modern meteorology. There are several possible 

 explanations. The first is that the surface westerlies ascend in 

 the north polar region in a huge slowly moving cyclone until they 

 meet the high level westerlies descending over the north pole in a 

 great inverted cyclone. The air from these two cyclones is assumed 

 to meet at an intermediate level, and is thought then to flow back- 

 wards towards the high pressure belt, and in its passage has to 

 force its way past the high level poleward current above and the 

 low level poleward current beneath. 



Of late years Dr. Shaw, the Director of the Meteorological 

 Ofl&ce in London, has suggested that there is little trace of any 

 effective circulation of the atmosphere between the latitudes of the 

 high pressure belts and the poles. He adduces in evidence of his 

 view that the westerly winds on the polar side of the high pressure 

 belts in either hemisphere blow for the most part from almost due 

 west to nearly due east. This, he maintains, is the case both at 

 the surface of the earth and also in the higher atmosphere, as 

 evidenced by the drifts of the cirrus clouds. On the other hand. 



