44 



GENERAL SCIENCE 



hole in the side of the bulb. Air will rush in, for the bulb was, as nearly as 

 possible, a complete vacuum. If the bulb is now placed on the stick it will 

 no longer balance. The air which has rushed into the bulb has weight. Dry 

 air weighs about J oz. per cu. ft. at sea level, or 13 cu. ft. weigh about 1 Ib. 



Air exerts pressure equally on all sides of objects. This has not 

 always been known. An Italian scientist by the name of Torricelli 

 found out how much the air weighs, or presses down on us. 



QUESTIONS 



1. What makes water gurgle from a jug? How can the gurgling 

 be prevented? 



2. Why is it better to have two holes in an oil can? in the stopper 

 of a large ink bottle? 



3. On what principle does the non-skid tire work? 



FIG. 37. Each little pocket in the tire becomes a partial vacuum as the tire 

 comes in contact with the pavement: a use of air pressure to prevent 

 skidding. 



4. Why is it necessary to force a knife under the cover of a 

 fruit jar before the cover will come off? What would be the effect 

 on the cover if the air were removed around the jar? 



5. Why do papers and dirt rise in the air after a swiftly moving 

 train? 



6. Why is it possible for a fly to walk on the wall? 



7. Explain the action of a fountain pen filler; self-filling 

 fountain pen. 



8. Why are you able to walk with tennis shoes more easily in 

 rough places than with high-heeled shoes ? 



