98 



IKtature'0 



By referring to Fig. 3 you will see why 

 the wind changes its direction when a storm 

 center passes over any point, It has not only 

 a spiral but also a forward movement. 



FIG. 3. 



Now let us go back to the barometer and see 

 what part it plays in predicting changes in the 

 weather. At the area of low pressure the air 

 is ascending, as we have seen, and, owing to 

 the peculiar way it ascends by circling 

 spirally upward around a region of compara- 

 tive calm it creates a partial vacuum, which 

 is more pronounced in the center of the area. 

 At the area of high pressure the air will be 

 condensed by the descending current being 

 arrested by the earth. The descending current 

 coming, as it does, from the upper and 

 colder regions accounts for the cool weather 

 that most always prevails at a high-pressure 

 area. In order to know how great the change 

 of weather is likely to be, we must know what 

 the readings of at least two barometers are 



