THE WARMING OF THE ATMOSPHERE 211 



places of high pressure to places of low pressure ; and so 

 the air is constantly in motion, tending to transfer its 

 heat and to equalize the atmospheric pressure. The 

 greater the difference in pressure between places, the 

 faster the movement of the atmosphere to overcome the 

 difference. 



The latitude of a place has much to do with the amount of 

 heat it receives. As the sun becomes .vertical to places 

 north of the equator, the length of the day in the northern 

 hemisphere increases, 

 and the time that a 

 place is in the sun- 

 shine is greater, so 

 that it receives more 

 heat from the sun. 

 On the 21st of June 



PICTURE TAKEN AT MIDNIGHT ON NORTH 

 CAPE 



The sun had not set even at midnight. 



all points within 



of the north pole, as 



at North Cape, have 



twenty-four hours of 



sunshine ; and the 



amount of heat received at the pole during these twenty- 



four hours is greater than that received at the equator, 



where the day is only about half as long. But so much of 



the heat is absorbed by the melting of ice and .the heating 



of the seas that have grown frigid during the six months of 



night that the sun's heating effect on the atmosphere is rela- 



tively small. 



Although the latitude of a place has much to do with the 

 amount of heat received, there are also many other things 

 which affect its temperature. This will appear when we 

 consider that Venice, Italy, with its mild and equable 



