CHAPTER III 

 THE ATMOSPHERE 



ATMOSPHERIC PRESSURE 



Close a bottle full of water with a one-hole rubber stopper through 

 which runs a glass tube. If we try to suck the water out of the 

 bottle, we find it is impossible to do so until the stopper is loosened 

 and air allowed to come in contact with the surface of the water. 



Our whole earth is enveloped by a 

 marvelous ocean of air, an ocean of 

 gaseous matter at least one hundred times 

 as deep as the water oceans. This air is 

 pressing down on us with tremendous 

 weight. It does not crush us because 

 our blood pressure, together with the air 

 in our body, is pressing out as hard as the 

 air is pressing on us. 



FIG. 28. Why will the 

 smaller test tube rise into 

 the larger? 



Fill a test tube about half full of water. Find 

 a smaller test tube which will just fit inside the 

 larger one. Invert the two with one inserted 

 in the other. As the water runs out, the inner 

 test tube must rise to fill the space. Why? 



Fill a tumbler nearly full of water, place a small 

 sheet of thick paper over the top, and hold it there 

 while you invert the glass. Remove the hand. 



Why does the paper remain on the mouth of 

 the glass? 



What holds the water in the glass? 

 What is trying to press the paper off? 

 Put the tip of your pencil carefully under the 

 paper just enough to make a slight opening be- 

 tween the glass and the paper. 



W T hy does the paper come off so quickly? 

 What other things do you find out from this experiment? 



39 



FIG. 28A. 



