322 SUGGESTIONS FOR WEATHER STUDY. 



On the completed map note the following : 



Cyclone. Chart of 14th January 1904. 



As we follow the general directions of the wind as indi- 

 cated by the arrows, we note they move anti-clockwise 

 with an inward bias. This is the characteristic type of 

 wind in a cyclone. The differences in force of the wind as 

 indicated by the different types of arrow are due to local 

 factors at the various places, but it will be noted that the 

 general trend is not altered. 



Next we observe that the lowest pressure is in the 

 centre of the area swept by the isobaric lines and that the 

 pressure increases regularly outward. This is the second 

 distinctive feature of a cyclone. At the centre there is a 

 dead calm. In this particular case the isobars are very 

 close, indicating a steep gradient of pressure. In a cyclone 

 the air rises ; in cooling by expansion, water vapour is 

 condensed and rain falls. As it progresses over an area, 

 the wind gradually changes its direction, and after the 

 centre is passed the weather clears (see Fig. 172). 



" The succession of the weather is the same in each 

 cyclone ; but the intensity of it depends on the gradient 

 of pressure. If of very great size and the diminution of 

 pressure in the centre very slight, gentle winds and light 

 showers only will be produced. If the cyclone is of small 

 dimensions (less than 100 miles across) and the diminution 

 of pressure in the centre is great, terrific winds and de- 

 luges of rain result." (Mill.) 



Anti-cyclone Chart of 3rd August 1908. 



Following the general wind directions we see here that 

 their trend is opposite to that of the cyclone ; that is, they 

 move in the directions of the hands of the clock. Further, 

 the arrows tend to point outward from the centre. 



Secondly, the highest pressure is in the centre, whilst 

 there is a regular fall outward. In this particular case 

 the gradient is much less steep than in that of the cyclone 

 quoted above. As to the weather characteristic of an anti- 

 cyclone we cannot do better than quote from Mill. In an 



