Pumps Pressure of Air. 71 



way down either through soft, loose ground or gravel, or 

 through crevices in the rock, and continues to sink until it 

 is stopped by rock or clay, which it cannot penetrate. 

 Therefore, if you should dig a pit or well down to a layer 

 of sand in which the water rests or moves, some of it will, 

 of course, flow into the well. 



3. Water is brought up from a well by 

 means of a bucket, or a chain pump, or a suc- 

 tion pump. 



4. A chain pump is composed of an endless 

 chain, which runs through a pipe. 



5. A suction pump is one in which the 

 water is made to rise by the weight or pressure 

 of the air. 



6. Air is everywhere, until it is displaced by 

 something else ; a cup or a pitcher, when said 

 to be empty, is full of air. 



7. Air has weight, and is moved just as 

 water and sand have weight and are moved. 

 Like water, air can be pumped. 



8. Air rests or presses on the land and also 

 on the water in the ocean, a cup, or a deep 

 well. 



9. If you should remove the air from any 

 spot on the water, you would see the water 

 suddenly rise just at that spot, showing the 

 pressure of the air on the surrounding portions. 



