CLOUDS. 29 



face of the earth, are prevented from rising into the 

 higher parts of the atmosphere. 



The light mists which are observed in serene 

 summer evenings are composed of the same kind 

 of watery exhalations, rendered visible by the 

 cooling of the air. In winter, when it freezes 

 sharply, rivers that are not yet frozen appear 

 to smoke, because the upper layers of water, on 

 account of their greater heaviness, sink to the 

 bottom, and cause the warmer water below to 

 rise to the top ; and the particles rising from the 

 warmer water assume the appearance of smoke. 



CLOUDS. 



When vapours rise to a height in the atmo- 

 sphere, and are collected in a dense state, they form 

 clouds, which float in the atmosphere at a greater 

 or less height, according to their weight. As 

 the atmosphere is heaviest 'below, dense and thick 

 clouds, which are on the point of melting into 

 rain, float near the surface of the earth, while 

 the thin fleecy clouds soar far above them. Both 

 kinds may be frequently seen at different heights 

 in the atmosphere at the same time. 



Clouds, being formed of water, are produced 

 in greatest abundance where the air has most 

 opportunity of acting upon water. Winds, there- 

 fore, which blow from the east and south-east, 

 over the Atlantic ocean, bring more clouds to 

 this country than westerly winds, which pass over 



the land. 



c 2 



