3H CAUSE OF THE DIURNAL 



oscillation, in the article above alluded to> remarks 

 that ' though in extra-tropical latitudes it is for the 

 most part so overlaid by casual variations as not to 

 be remarked in a single day. On the other hand, 

 between the tropics, and especially in the equatorial 

 regions, its regularity of progress is most striking. 

 Thus, Colonel Sykes remarks that, among many 

 thousand observations taken personally by himself on 

 the plateau of the Deccan there was not a solitary 

 instance in which the barometer was not higher at 

 9.10 A.M. than at sunrise, and lower at 4.5 P.M. than 

 at 9.10 A.M. whatever the state of the weather, &c., 

 might be.' 



It will be observed that the action of the forces of 

 solar and astral gravitation in causing these oscillations 

 of pressure, is dependent on the course of the upper 

 currents of the atmosphere being such as we described 

 in section 46. And it appears to us that, if any fur- 

 ther arguments beyond those given in vol. i. were 

 requisite to show that those currents actually are 

 such as we there described, then these diurnal oscil- 

 lations of the barometer might not unreasonably be 

 accepted as convincing proof that such is actually 

 the course of those currents. 



Halley, as quoted by Dove in his c Law of Storms/ 

 page 38, says that the 'north-east trade wind below 

 will be attended with a south-westerly above, and 

 the south-easterly with a north-westerly above. 1 

 And Dove also appears himself to be of the same 



