1S4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



pressures in the exterior calm atmosphere, we shall have the depres- 

 sion 



D = Po ~ Po (7) 



which relates to the horizontal current in the upper stratum. The 

 excess of the pressure D in the barometric maximum is given by the 

 formula 



D = P - P' (8) 



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 II be the reduced 

 pressure, we have 



n - Po +q (9) 



p' - Po' + q' (io) 



writing 



E = n - p (11) 



we shall find 



D +E+D=q-q> (12) 



The quantity E represents the vertical depression in the descending 

 current, and this last equation shows us that the difference between 

 the weights of the columns of air produces the motion of the three 

 currents. 



(3) System of cyclonic winds. 



This system has circular isobars around a barometric minimum 

 at the surface of the earth; in the upper strata it has a barometric 

 maximum. The air flows in along the surface of the earth from 

 all sides and the horizontal currents are changed little by little into 

 vertical ascending currents. At a certain height the vertical motion 

 is changed into a horizontal motion and in the upper strata the air 

 flows out from the barometric maximum. By introducing the same 

 notation as we have employed in the first system of parallels, equa- 

 tions (1) to (6) hold good also for cyclones. 



(4) System of anti-cyclonic winds. 



Tins system has isobars circular around a barometric maximum 

 at the surface of the earth: it has a barometric minimum in the 

 upper strata. The upper air flows inward toward the barometric 

 minimum and the horizontal currents in the upper strata are changed 

 little by little into descending vertical currents. The vertical 

 motion then changes into a horizontal motion and the air flows out 

 from the barometric maximum at the surface of the earth. Equa- 

 tions (7) to (12) hold good for anti-cyclones. 



