ScHAw. — Australasian Wcatlier-charts and N.Z. Storms. 65 



hemisphere), and as the motion of translation is uniformly to 

 the eastwards and northwards, although frequently obstructed, 

 or even reversed, for a time by opposing anti-cyclones, it is 

 clear not only that the circulation is according to law, but 

 also that the maintenance of the circulation, and also of the 

 onward march, it may be, are due to some force developed 

 within the cyclone itself. The origin of a whirlwind in a hot 

 region is simple. Some locality under special conditions gets 

 excessively heated by the sun, and an upward current is pro- 

 duced. From all sides cooler air flows inwards and upwards, 

 and so a spiral upward motion is produced, either right-handed 

 in this hemisphere or left-handed in the Northern Hemisphere. 

 But what is the cause of our cyclonic storms, which reach us 

 from the west and apparently from the south? They cannot 

 be due to any such superheating of the ground, for all is sea 

 until we reach antarctic ice-clad land. I put forward the 

 following suggestion, partly derived from the ideas of various 

 writers on the subject and partly from my own ideas. 



I conceive that our cyclones have their birth on the con- 

 fines of the antarctic region — at the meeting-place of the 

 north-west counter trade-winds with the low-level outflow from 

 the south polar anti-cyclone. Where these opposing currents 

 meet they cannot glide one over the other as in the case of 

 the high-level currents which form anti-cyclones, because of 

 the presence of the superincumbent atmosphere ; therefore 

 they form a calm neutral mass between them, and by the con- 

 stant pressure both are forced upwards, each being deflected 

 strongly in this high latitude to the left, outside the calm 

 column of air, and so producing the right-handed upward 

 spiral, in which motion the central column itself may partake. 

 But as the air ascends temperature and pressure decrease, 

 until the water-vapour is condensed into rain or snow or hail, 

 and the latent heat is given up to the surrounding air, which 

 expands and rises, and causes a stronger upward draught. 

 This condensation and liberation of latent heat would be 

 greatly accelerated by the presence of suow-clad land at the 

 meeting-place of the winds, and it may be that in some favour- 

 able spots on the coast-line of Antarctica high cliffs and glaciers 

 meet the force of the vapour-laden west winds and act as the 

 primary determining influence by forcing the west winds up- 

 wards, and, by condensation of the vapour and consequent 

 warming of the air, increasing the upward current. At the 

 level of the surface of the land the force of the opposite current 

 would be felt, causing first gyration and then northerly motion 

 of the whole gyrating system, which would be borne eastwards 

 and northwards by the prevailing westerly winds — northwards 

 because the southern edge of the storm-whirl is circulating 

 against the west wind while the northern edge is circulating 

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