SCIENCE OF COMMON THINGS. 69 



What is the atmosphere ? Why mountains appear blue. 



CHAPTEE Y. 



THE ATMOSPHERE. 



433 What do we understand by the atmosphere f 



The thin transparent fluid which surrounds the earth 

 to a considerable height above its surface, and which, 

 by its peculiar constitution, supports animal life by 

 respiration, and is also necessary for the due exercise 

 of the vegetable functions. 



433 Is the atmosphere invisible f 



It is generally, but erroneously, so regarded. The 

 atmosphere is not invisible. 



434 How can you prove that the atmosphere is not invisible f 



Because when we look upwards into the firmament on 

 a clear day, the space appears of an azure or clear color. 



This color belongs not to anything which occupies the space in which 

 the stars or other celestial objects are placed, but to the mass of .air 

 through which the bodies are seen. 



435 Why do distant mountains appear Hue f 



"Not because it is their color, but because it is the 

 color of the air through which they are seen. 



-36 Has air weight f 



It has / as well as lead, stone, or any other material 

 substance. 



437 How can this be readily proved? 



By weighing a vessel filled with air, and the same 

 vessel after the air has been exhausted from it. 



438 Can the existence of air be known by the sense of touch or feeling f 



It can ; since it opposes resistance when acted upon, 

 and strikes with a force proportionate to the speed of 

 its motion. 



438 Why do we always feel a breeze on the deck of a steamboat in 

 motion, even upon the calmest day t 



Because our bodies forcibly displace the air as w$ 

 are carried through it, 



4 



