EFFECT OF EARTH'S ROTATION 



147 



understood if the conditions of this moving body of air 

 are considered. 



As the earth is about 25,000 miles in circumference and 

 turns on its axis once in 24 hours, a body situated at the 

 equator is carried from west to east at the rate of about 

 1000 miles per hour, whereas a body at the poles simply 



A SAILING VESSEL. 

 Showing how the wind is used in commerce. 



turns around during a revolution. Thus as we go on the 

 surface from the poles toward the equator, each point has 

 an increasing west to east velocity. 



A body of air, not being attached to the surface, will 

 have this west to east velocity imparted to it very slowly 

 by friction. Thus as it goes from higher to lower lati- 

 tudes, it will lag behind particles on the surface which 

 have this west to east velocity, and so will appear to have 



