ELEMENTS OF GENERAL SCIENCE 



PART I. THE AIR 



CHAPTER I 

 SOME CHARACTERISTICS OF THE AIR 



1. Air as material. Most of the time we are quite uncon- 

 scious of the air with which we are surrounded. In fact, we 

 usually ignore the existence 

 of the air, for if there is a 

 glass tumbler on the table 

 before us and this does not 

 contain either a liquid or a 

 solid, we say that it is empty. 

 It is not empty, for it is 

 filled with air, but since air 

 is not visible, we ordinarily 

 do not recognize its presence 

 (fig. 1). Similarly, we often 

 say, when we look out over 

 the houses, tree tops, and 

 open fields, that " there is 

 nothing there," but if we go 

 out of doors on a windy day 

 we may be very forcibly reminded that there is something there. 



If we examine a bicycle tire or a football empty of every- 

 thing but air, we may find proof that air does really fill things, 

 for everyone knows that when you attempt to flatten out an 

 inflated football or tire, it resists and shows evidence of being 



l 



FIG. 1. An experiment with air 



If an inverted drinking glass is forced 



downward into water, the air within the 



glass keeps the water from entering 



the glass 



