MOVEMENTS OF ATMOSPHERE GULDBERC, AND MOIIX I S3 



earth from both sides toward the barometric minimum and the 

 horizontal current is gradually changed into a vertical ascending 

 current. At a certain altitude the vertical current is changed into 

 a horizontal current which flows outward from the barometric 

 maximum. Denoting by p the pressure at the lower barometric 

 minimum and by p the pressure at the upper maximum and by 

 p ' and p' the corresponding pressures in the exterior atmosphere, 

 we shall have for the depression D which belongs to the horizontal 

 current along the surface of the earth, 



D = Po - Po (1) 



The excess of the pressure D in the upper barometric maximum 

 is given by the formula 



D-p-pr (2) 



Let q and q' be the weights of the columns of air of the vertical cur- 

 rent and of the calm atmosphere, respectively, and let 77 be the 

 reduced pressure (see §18) we have 



n =p +q (3) 



Po - P' + q' (4) 



e = p - n (5) 



in which we call E the vertical depression of an ascending current 

 (see § 1 8). 



From these equations we obtain 



D + E + D = q' - q (6) 



This last equation shows us that the difference in weight of the col- 

 umns of air produces the motion of the three currents. 



(2) System of descending parallel winds. 



This system (see fig. 19) has rectilinear isobars and a barometric 

 maximum at the surface of the earth and a barometric minimum in 

 the upper strata. The air flows in from the two sides toward the 

 barometric minimum and the horizontal current in the upper strata 

 changes little by little into a descending vertical current. The ver- 

 tical current then changes into a horizontal current which flows 

 out from the barometric maximum at the surface of the earth. 



Denoting by p the pressure at the barometric minimum and by 

 p the pressure at the maximum and by p f and p' the corresponding 



