292 CAUSE OF WIND. 



rushes (under the door, and through the 

 window crevices) into the room. 



Q. Give me an ILLUSTRATION. 



A, If I dip a pail into a pond and 

 fill it with water, a hole (or vacuum) is 

 made in the pond as big as the pail ; but 

 the moment I draw the pail out, the hole 

 is filled up by the water around. 



Q. Show how this illustration APPLIES. 



A. The heated air which ascends from 

 the bottom of a room, is as much taken 

 away, as the water in the pail ; and (as 

 the void was instantly supplied by other 

 water in the pond} so the void of air is 

 supplied by a current from without. 



Q. What is the CAUSE of WIND ? 



A. The sun heats the earth, and the 

 earth heats the air resting upon it; as 

 the warm air ascends, the void is filled 

 up by a rush of cold air to the place, and 

 this rush of air we call WIND. 



Q. Does the WIND ALWAYS blow ? 



A. Yes ; there is always some motion 

 in the air ; but the violence of the motion 

 is perpetually varying. 



