The Audubon Societies 



55 



may be dense, thai is, thick and jiressi'd loL^ctluT, or. on the contrary, thin 

 ^nd light. 



If the air all o\-er and around tlir carlh was of exactly the same degree of 

 heat or cold (teni})eraturi'), and of exactly the same weight (pressure), and of 

 exactly the same wetness or (lr\-ncss (liuniidity), as well as of exactly the same 

 thickness (density), it would ha\-e no motion at all and there would be only 

 one kind of wi-alher e\erywheri'. 



liut this is ne\-er the case. The air nia\- be \ery heax'V in one place and 

 \-erv li.siht in another; or, it nia>' be (|uit't where you li\-e, whiU' nio\in,i,f at a 



HIRD-HOX PROTIXTED ^■R()^t CXI'. 



IMu.tOKraphcd by H.nvaril H. Cleaves 



furious rate elsewhere; it may even be freezing cold about the polar seas, and 

 at the same time summer-warm near the Gulf of Mexico. 



All of these states, or conditions, of the air, taken at the same time but in 

 diflferent places and at different heights (altitudes), are what is called the 

 weather, and it is very important to understand all we can about the weather, 

 since we are obliged to live on this earth in weather which constantly changes. 



The air in motion is called wind. When the wind blows hard, we really 

 hear that ]xirt of the weather. The air full of water-vapor falls upon us in 

 rain or snow, according as it is warm or cold. When it rains or snows, we can 



