DYNAMICS OF CYCLONES and ANTICYCLONES. L55 



driven one the reverse is the case, the air in I lie outer parts moving quicker than the air 

 m the inner. Judged by this teat the evidence is entirely in favour of the theory that 

 cydoaes aire oonveotionally driven. An examination of the diagrams in the Report <>/ 

 the International Cloud Observations above referred to show in a marked way that 

 in cyclones the velocity of the wind increases towards the centre. These charts do 

 mil show any great increase of velocity towards the centre <>f the winds at the surface 

 of the earth, but they show thai as we ascend to greater elevations the increased 

 velocity becomes mora marked, and is very great at the strato-cumulus level, and up 

 through tin- cirro cumulus, alto cumulus, alto-stratus, and into the cirro-cumulus level, 

 ;i result we would not expect to find if cyclones were dynamically driven. 



There is another point in connection with the source of energy in cyclones to which 

 reference may be made here, and which seems to support, the above conclusion. It 

 ojolones are convectionally driven we would expect them to lend to form and move 

 over areas where the air is relatively hot, or moist, or both. II' we examine Dr 

 Buohan's maps of the isobars and winds of the world, and his corresponding maps of 

 the isotherms, and also Dunwoody's maps of the storm tracks of the world, all in 

 Bartholomew's Physical Alius, Vol. III., we will find this supposition receives con- 

 siderable support. Confining our attention to the area over Europe and the eastern side, 



Of the Atlantic, it will be seen thai in winter the general air circulation over this area, is 

 from the south west, blowing OUt of the high-pressure area, situated at this season to 



the south-west of Spain. It, is this warm south-westerly wind that carries the high 



temperature at this season northwards to Iceland and Scandinavia, and gives rise to the 

 lipcurving over this area, of the isothermal lines shown in the maps, and this hot moist 



air, driven northwards between the cold air on both sides, would seem to be the cause 



and SOUTOe of energy of the. cyclones which tra.verse this area, during the. winter months. 

 The maps of the storm tracks show that the storms coming towards our area, from 

 the western Atlantic move generally along one track till they pass Newfoundland, 

 where the track divides ill two, and the storms travel over one of the two routes. 

 A number of them go north-eastwards over Scandinavia, whilst the others move across 

 England and eastwards over the Continent. Confining our attention tO the more 

 northerly route, it will lie seen from the maps that, during winter this track is at its 

 furthest north position. In summer the conditions become somewhat, changed, the 



general circulation does not blow so much from the south, the winds being at this 



on ahout west-south-westerly, and the isol hernial lines no longer curve, northwards 

 to the extent, they did iii winter, and the track of the storms is now situated at its 

 furthest south position, the relatively hot and moist air being now more to the south 

 than it was in winter. From this it will he seen thai, the track of the cyclones over 

 our area moves northwards as the isothermal lines curve northwards with the approach 

 of winter, and again coming southwards when the isotherms lend to 1 1 a, ve an east and 

 westerly direction, the storm track thus keeping over the relatively hot, and moist area,. 



VOL. XL. PART I. (NO. 7). Y 



