34 CAUSE OF THE DIURNAL 



opposing forces of solar and astral gravitation, pro- 

 vided that the general course of aerial currents be 

 that which we have described in section 46. 



For the forces of attraction just mentioned tend to 

 raise aerial tides, and diminish atmospheric pressure 

 on those parts of the earth's surface which may be 

 turned in the direction of their influences respec- 

 tively*. And as, according to section 46, excepting 

 the lower strata of air in each of the temperate 

 zones, the general tendency of the whole mass of the 

 atmosphere is westwards : 



: . Therefore, on that part of the earth's surface which 

 lies east of the sun that is to say, on that part of 

 the surface which is moving from the point of noon 

 to the point of sunset the tidal action of the sun 

 acts in conjunction with the aerial currents, drawing 

 .them towards it in the natural direction of their 

 Bourse, and therefore tending to diminish rather than 

 4o cause increase of pressure. Whereas, on that 

 part of the earth's surface which lies west of the sun 

 * moving from the point of sunrise to the point of 

 noon the tidal action of the sun acts in opposition 

 to the general course of the aerial currents, dragging 

 against and tending to retard them, and tending 

 therefore to cause, by this opposing action of attrac- 

 tion and vis inertias forces, an increase of pressure 

 upon the barometer between the hours of sunrise and 

 noon. 



And, in precisely the same manner as that in which 



