230 Prof. Dove's Outlines of a general Theory of the Winds. 



the westerly wind in the northern hemisphere through NW. 

 to N., in the southern through SW. to S. Hence the varia- 

 tion will be 



for the northern hemisphere, S. SW. W. NW. N. 

 for the southern hemisphere, ~\ -wr ;njw w ow q 



on the contrary J 



From the whole of the phenomena observed, the following, 

 consequently, is the result : 



A. In the northern hemisphere the wind turns, if polar 



currents and equatorial currents take place alternately, 

 upon an average in a direction S. W. N. E. S. through 

 the points of the compass, and it springs back between 

 S. and W. and between N. and E. more frequently 

 than between W. and N. and between E. and S. 



B. In the southern hemisphere the wind turns, if polar cur- 



rents and equatorial currents take place alternately, 

 upon an average in a direction S. E. N. W. S. through 

 the points of the compass, and springs back between 

 N. and W. and between S. and E. more frequently 

 than between W. and S. and between E. and N. 

 Hence follows : 



a. Where in the tropical zone only polar currents prevail 



on the surface, there is no complete rotation, but an 

 unchanged deviation proportional to the distance of the 

 place of observation from the outward limits of the 

 current, which is only modified a little by the variation 

 of that limit in the seasons. These are the trade-winds. 



b. Where in the tropical zone, by the peculiar distribution 



of the solid and fluid, a southerly current alternates once 

 a year with a northerly one, there is only one rotation 

 in the whole year. These are the monsoons. 



c. In the temperate, and probably also in the frigid zones, 



where equatorial currents continually alternate with 

 polar currents, the wind changes upon an equal average 

 and more frequently in a fixed direction through the 

 points of the compass, but in the northern hemisphere 

 exactly in an opposite direction to that in the southern. 

 This is the phenomenon which I have denominated the 

 law of rotation. 

 It is evident then that the relations of the tropical winds 

 are the most simple case of the law of rotation. 



The preceding discussion does not depend on the origin 

 of the motion of the mass of air contained between the observed 

 parallels, whether we suppose it to be contemporaneous in all 

 points of the same meridian, or successive, by suction or 



