HUMPHREYS: METEOROLOGICAL PARADOXES 



155 



other tangential to the path of travel. The first, like the de- 

 flective force and the centrifugal force, has no effect on the speed, 

 being at right angles to the direction of motion, while the second 

 steadily increases the speed, which, in turn, increases the de- 

 flective force and the deviation towards the east. In the end, 

 therefore, the component of p along the path reduces to zero, 

 and the direction of travel becomes exactly east. Hence winds 

 that are continuous for even a few hours always blow more or 

 less closely along isobars, that is, at right angles to, and not in 

 the direction of, the sustaining force — around centers of pres- 

 sure minima and maxima and not directly towards or from them. 



/> cos a-i-c 



Fig. I. Diagram showing deflection of particle of air towards the east. 



No matter, therefore, how paradoxical it may be, air pushed 

 north does blow east (in the northern hemisphere), pushed east 

 blows south, pushed south blows west, pushed west blows north; 

 while in the southern hemisphere it blows exactl}^ contrariwise. 



RAIN DRIES THE AIR 



As everyone knows, there is continuous and often rapid evapo- 

 ration from practically all parts of the earth's surface. Never- 

 theless, the atmosphere as a whole never becomes even ap- 

 proximately saturated. Water, as just stated, is always evap- 

 orating into the air and thus constantly tending to saturate it; 

 but, on the other hand, the air is forever being dried by the pre- 

 cipitation out of it of rain, snow and other forms of condensation. 

 Whatever the temperature and relative humidity of a given mass 

 of air at any place along its convectional route, the total of water 

 vapor it then contains obviously is less, in general, than when 



