GKXERAL CIRCULATION OF THE ATMOSPHERE 275 



in several directions and start the lines at different parts of the card- 

 board, Notice that every pencil line and every ink line, wherever it 

 starts and whatever its direction, curves always to the right. This 

 is because the cardboard moves to the left under the marble or pencil 

 as they travel. 



300. Right-hand Deflection of Winds in the North Hemi- 

 sphere. In Ex. 61 the revolving cardboard represents the north 

 hemisphere of earth and the center nail represents the north 

 pole. Any wind anywhere in the north hemisphere, starting 

 in any direction, will, under 

 natural conditions, always 

 follow a curved path over 

 the earth, as the marble or 

 pencil did over the revolv- 

 ing cardboard; because the 

 rotating earth moves side- 

 wise from under the wind 

 as it travels, just as the 

 cardboard moved from un- 

 der the marble or pencil. 



It is through the applica- 

 tion of this general law that 

 we are able to explain: (1) 

 That the trades in the 

 northern hemisphere are 

 northeast winds instead of north winds; (2) that the return- 

 ing upper currents are southwest winds instead of south 

 winds (see Fig. 202) ; (3) that the ground winds about a HIGH 

 blow spirally outward, curving to the right, instead of blowing 

 straight out from the center of the HIGH (see Art. 291); and 

 (4) that the winds blow into the LOW from every side in 

 curved, fish-hook shaped paths (see Fig. 189). 



The path of any portion of air blowing into a LOW is ex- 

 plained by Fig. 204. Let x mark the center of the LOW. The 

 air at a is being pushed straight toward c and x by the sur- 

 rounding higher pressure; but the deflecting force (Art. 299) 



FIG. 204. Analysis of the cause of the 

 counter-clockwise whirl about a low in 

 the Northern Hemisphere. 



