CIRCULATION OF AIR 



215 



made charts of the weather conditions over the entire 

 surface of the earth. Every year more and more data are 

 being collected and these charts are becoming more and 

 more reliable. 



These charts are of great value, since they aid in the 

 explanation of climatic conditions in different parts of the 

 world. The results 

 of the data thus 

 gathered together 

 have been of untold 

 service to commerce 

 and each year have 

 saved many lives and 

 a vast amount of 

 wealth. 



Circulation of Air. 

 The atmosphere is 

 the circulatory medi- 

 um of the earth, as 

 blood is for the ani- 

 mal and sap for the 

 plant. Without it 



the activities of the earth would stagnate. It scatters the 

 seeds of plant life over the face of the earth. It carries 

 water evaporated from the sea to the land, replenishes the 

 underground reservoirs for man's use, and transports 

 reserve supplies to the mountains for the use of cities, 

 for power, and for irrigation. It cools the hot regions 

 with the invigorating breath from the mountains and from 

 the uniformly tempered sea. It warms the cold places by 

 bearing to them the heat taken from the warmer ocean 



A SAILING VESSEL 



Both the sailing vessel and the steamship are 

 dependent for power on movements of the 

 air winds and drafts. 



