IX 



Climates of the World 



149 



particles of ice is commonly seen round the Sun or Moon. 

 Later the sky becomes gloomy, the air feels warm and 

 oppressive even in winter, thick clouds form, and there is 

 heavy rain, while the barometer is all the time falling, and 

 the wind shifting its direction. As soon as the barometer 

 begins to rise, the centre of the cyclone has passed ; and 

 as the atmospheric pressure increases in the rear of the 

 depression the sky clears, the wind freshens, and the air 

 feels peculiarly exhilarating. Fig. 30 shows the form 



Cirrus 



;RONT 



REAR 



FIG. 30. Isobars of a Cyclone. (After the Hon. Ralph Abercromby.) Direction 

 of wind and distribution for weather shown for the north temperate zone. 



of the isobars, direction of wind, and the' different condi- 

 tions of weather in various parts of a cyclone. It shows 

 what changes an observer would notice according as he 

 was to the north or south of the cyclone as it passed. The 

 long arrow shows the direction in which it moves. In a 

 typical cyclone, such as that represented, the gradients are 

 always steeper in the rear than in the front, so that the 

 strongest winds are experienced after the barometer has 

 begun to rise. The succession of weather is the same 

 in every cyclone ; but the intensity of it depends on the 



