THE WEATHER 



to west. Instead of moving straight towards 

 the south as a north wind, it will move towards 

 the south-west, and thus become a north-east 

 wind. On the other hand, the air which flows 

 away from the centre of the anti-cyclone towards 

 the north, passes over regions of the earth which 

 are travelling less fast in the daily rotation than 

 the places whence the air came. The air then 

 seems to be coming in the same direction in 

 which the earth revolves, and the south wind 

 becomes a south-west wind. In this way the 

 whole of the air spreading outwards gets a 

 clockwise swirl, and the observed movements 

 are explained. 



We still have to consider why an anti-cyclone 

 should permanently exist over the continent of 

 Europe and Asia during the winter months. 

 We have seen that these vast stretches of land 

 get very cold in the winter. The air lying over 

 them gets cold likewise, and therefore, as we 

 know, becomes heavier than the warmer air in 

 other places. It therefore tends to sink and 

 flow outwards over the ground, giving rise to a 

 high-pressure system and the arrangement of 

 winds we have described. The anti-cyclones 

 that are observed over the British Isles are of 

 two kinds. They may be small and local, when 

 they will probably soon disappear, or they may 

 be parts of the great permanent continental anti- 

 cyclone, when we may look for a long spell of dry 

 settled weather, with north-east or easterly winds. 



(69) 



