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



It is evident that since an equilibrium so produced cannot be 

 a lasting one, barometrical maxima and minima lie in general 

 close to each other : such irregularities generally, after various 

 previous oscillations, balance each other. 



If the equatorial currents be detained by a high land situ- 

 ated in the south, the quiet and dry sea of air of such districts 

 will be moved principally by the influx of waves of the west 

 and east winds traversing the parallels. Besides it is evident 

 that the number of east winds will here increase, while the 

 number of west winds will decrease. 



The range of the barometrical oscillations of such districts 

 can be but very small. 



The necessity of the origin of equatorial currents in the 

 temperate zones has already been treated of in a former me- 

 moir on monsoons and trade winds. The frequent occurrence 

 of the SW. winds in comparison with the southern wind is a 

 proof that the equatorial currents, when they are first observed 

 at the surface, could not have originated there, but must have 

 come down from above. M. von Buch has also mentioned 

 in support of this view, proposed by Halley, such convincing 

 reasons, grounded on observations made at the Peak of Te- 

 neriffe, that it has been received by almost all naturalists. The 

 necessity of such westerly winds following from the constancy 

 of the rapidity of rotation of the earth has recently been 

 made so evident by Herschel, jun., that it will be proper to 

 cite here the words of the author. 



" The constant friction thus produced between the earth 

 and atmosphere in the regions near the equator must (it may 

 be objected) by degrees reduce and at length destroy the ro- 

 tation of the whole mass. It is easy to see in the present 

 case where and how the compensation takes place. The 

 heated equatorial air, when at length it returns to the surface, 

 in its circulation, which it must do more or less in all the in- 

 terval between the tropics and the poles, will act on it by 

 its friction as a powerful south wind in the northern hemi- 

 sphere, and a north-west in the southern, and restore to it the 

 impulse taken up from it at the equator." 



The view developed in this memoir respecting the phe- 

 nomena relative to wind which occurs in the temperate zones, 

 removes, if I mistake not, the objection raised against the 

 theory of the trade-winds, that the influence of the rotation of 

 the earth could not be so considerable in the latitudes in which 

 they prevail, because it must be much stronger in higher de- 

 grees of latitude than between the tropics. The objection 

 in effect is none, for I think I have demonstrated that that 

 which is required does really exist. We can also easily ac- 



