146 MR JOHN A1TKEN ON 



the anticyclone than we have been giving, as a study of the area under its influence 

 will probably assist in forecasting the movements of the cyclone and the weather 

 conditions generally. 



An examination of the weather charts for the winter months over our area shows 

 that when the temperature is low over any part of it, particularly over the Spanish 

 Peninsula and over the north-east of Europe, that as the temperature falls the 

 pressure rises — that is, whenever the temperature falls below the mean, an anticyclone 

 forms over the cold area, increasing in pressure as the cold strengthens. And, on the 

 other hand, when the temperature begins to rise the pressure falls. It must be 

 admitted that there are difficulties in studying this subject, as there is not at present 

 sufficient information to enable us thoroughly to study the point. We would require 

 a complete record of the clouds over the area, so as to enable us to judge how far the 

 earth's radiation initiates the change. But I think it may be accepted that, as a rule, 

 any extreme cold over our area is generally accompanied by a small amount of cloud, 

 and that the cold is due to radiation. An examination of the weather charts shows 

 that, on some occasions, when the directive force of the cyclone was small, a rise of 

 temperature in the anticyclonic area, by weakening the high pressure, caused the cyclone 

 to move towards it. On the other hand, a decrease in temperature in the anticyclone 

 may force the cyclone back. These charts also show that, if the temperature over both 

 the Spanish Peninsula and the north-east of Europe falls very low at the same time, 

 then the whole of Europe comes under anticyclonic conditions, the cyclones being 

 driven from our area. 



Let us now turn to the general question of cyclonic circulation, and see if what 

 has been stated helps us to understand some of the other phenomena associated with 

 cvclones and anticyclones. We have seen that the upper winds, circling from the 

 anticyclones and to the cyclones, by moving more quickly, and by moving at an 

 angle across the lower air, tends to prevent the latter rising, even though it be the 

 lighter. The effect of this, as already pointed out, is to drive the hot moist air lying 

 near the earth's surface to the circumference of the anticyclone, where it is picked up 

 by the cyclone, and as the spirally moving cyclonic winds also tend to prevent the 

 lower air rising, the hot, moist air is swept into the front of the low-pressure area, 

 and the upper winds here cross the lower at a considerable angle, the hot moist air is 

 compelled to keep near the ground, and, further, the air near the ground having a 

 less tangential force, it is drawn into the centre of the depression, where it is drawn 

 up, and as we saw in the experiments, forms the core of the cyclone. By this method 

 of arranging the air in layers, the cyclone gets the best efficiency out of its material, 

 the pressure falling from the circumference to the centre, whilst the temperature 

 rises towards the centre of low pressure. 



The effect of cyclonic circulation in keeping the hot moist air near the ground 

 explains why the air in front of a cyclone is always hotter and moister than the 

 air in the rear. The lower air sent forward by the anticyclone is swept off its 



