WINDS AND STORMS 



141 



than an adjacent body of water. The air above the 

 land also becomes Avarmer and expands more than 

 that over the water. This expansion reduces the pres- 

 sure and causes the air to move toward the land from 

 the water. This movement of the air is of great value 

 along denseh- populated sea coasts or lakes. This sea 

 breeze, as it is called, lowers the temperature and also 

 brings in pure air. 



At night the land cools more rapidly than the water. 

 Consequently breezes bloAv from the land to the water. 



Cyclones. The regularity of the general system of 

 prevailing winds is frequently disturbed by local and 

 temporary disturbances which are called storms. These 

 are brought about 

 by the fact that the 

 atmospheric pressure N 

 is not the same in all 

 places at the same 

 time. For example, 

 if we should receive 

 reports of baromet- s 

 ric readings from a 

 number of places in 

 the United States 

 taken at the same 

 time, we should find 

 that they were not all alike. In some parts of the coun- 

 try the readings would be high, in other parts low. As 

 a result of the differences in pressure, there is always 



FIG. 53. Diagram to show the cir- 

 culation of air about a low and about a 

 high. The rotation of the earth turns 

 the currents 9f air to the right in the 

 northern hemisphere and to the left in 

 the southern hemisphere. 



