ATMOSPHERIC PRESSURE 



57 



pieces of glass and fills the entire space. When there is 

 no air between the pieces of glass, there is no air pressure 

 tending to sepa- 

 rate them, and it 

 is with great dif- 

 ficulty that you 

 can pull apart the 

 two pieces. This 

 is because the air 

 on the outside is 



E atmospheric 

 pressure 



glass- 



, v i i Explain this diagram. Can you mention any other 



W 1 1 n a devices that make use of this same principle ? 



pressing them to- 

 a 



force of about 

 fifteen pounds to the square inch. After you fill a bottle 

 with water, put a small piece of wet paper on top and 

 invert it, what happens? Why? Application of this 

 principle is made in the disks used for coat hangers, 

 supports for shelves in display windows, and the ash tray 

 that clings to the wind shield of the automobile. 



A very famous experiment was tried in Magdeburg 

 (mag'de-boorK), Germany, in 1650. Two metal hemi- 



Eiplain this renowned experiment with the Magdeburg hemispheres. 



