INTERESTING THINGS ABOUT THE AIR 13 



may be much harder by noon, as if more air had been put 

 into it. The same thing will occur if the machine is allowed 

 to stand in the sun. The additional pressure may, indeed, 

 become so great as to burst the tire. Of course it is very 

 clear that no air has been added to that which was in the 

 tire in the morning, for if the rubber will retain the air 

 which is in the tire, it will be equally effective in preventing 



FIG. 12. Air pressures at different elevations 



The illustration shows Mt. Rainier, Washington, from 5500 feet to the summit. 



The figures show the elevations at different points and the air pressures at these 



points. Note the decrease of air pressure with the increase of elevation 



more from entering. Since such an increase of pressure as 

 we have been describing occurs only when the tire has been 

 heated by contact with the hot road or by direct exposure 

 to the sun, it is fair to conclude that when the air is heated 

 it has greater tendency to expand and that it therefore presses 

 harder against the walls of the tire and would expand if it 

 were not confined by the tire. 



The notion that air expands when heated ought to be 

 tested before we accept it finally. This may be done in 



