WHAT MAKES THE AIR USEFUL TO MAN? 45 



barometer started a long line of applications in the use of 

 this instrument. The heights of mountains can be meas- 

 ured and weather changes can be foretold. The air pilot's 

 altimeter is a type of barometer with a scale marked off in 

 distances above sea level. The various things that scien- 

 tists have found out about the air have been used in thou- 

 sands of ways to make life more efficient and comfortable. 



air* 



PROBLEM I. WHAT MAKES THE AIR USEFUL TO MAN? 

 Demonstration 1. Does Air Occupy Space? 



Cut the bottom from a narrow-necked pint bottle. 1 Stretch the 

 open end of a rubber balloon over the mouth of the bottle. Close 

 the clamp over the neck of the bal- 

 loon near the neck of the bottle. 



Thrust the large open end of the 

 bottle down into a quart jar half full 

 of water. 



a. Does water enter the bottle? 



b. Does the level of water change 

 in the jar? 



c. Explain. 



Open the clamp on the rubber 

 balloon. Notice three things that 

 happen as a result. 



d. Record these three changes. 



e. If you find any evidence to 

 prove that air occupies space, ex- 

 plain what it is. 



Air Is All about Us. Air 



makes an envelope for the earth 



that extends high above us. 



Those of us who have climbed a 10,000-foot mountain 



know how hard it is to breathe as we near the summit. 



We say that the air has become thin. As a matter of 



fact if one could rise above sea level at will, he would 



eventually pass out of the atmosphere into space where 



1 Process explained on page 77. 



