"WINDS. 



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change was effected by heating water and then cooling it, when it came 

 back to water again. This watery vapour is always present in the atmo- 

 sphere. Heat, also, is present in the atmosphere, and the sun is the origin 

 of that heat. 



Heat, we know, is the effects of the rapid motion of small particles of 

 matter, and is radiated from our bodies so we feel cold ; it reaches our 

 bodies, and we feel warm. So air is heated or cooled by the sun, not in its 

 absence, except when the earth and air have been so warmed during the day 

 that the heat is given out by them long after sunset. We have read of the 

 pressure of the atmosphere in the PHYSICS section, and that warm air is 

 lighter than cold air, as shown in the ascension of the Montgolfier balloon. 



714. High tide and storm on the coast of Schleswig. 



It is this variation of temperature of the atmosphere that gives birth to one 

 great meteorological agent viz., the WIND, which we will now consider. 



WINDS AND AIR CURRENTS. 



We can easily illustrate the cause of winds. Suppose we have a hot 

 room and a cold one, and we suddenly open the door of communication 

 between them, the heated air which has risen to the ceiling of one room 

 will rush out through the upper part of the opening of the door, and the 

 cooler current will flow in just above the floor. If we place a lighted candle 

 in the upper and lower part of the opening we shall see the flame tending 

 outwards from the heated room, and in an opposite direction from the cold 

 room. In the centre of the open door there will be but slight disturbance. 



