MOVEMENTS OF ATMOSPHERE GULDBERG AND MOHN 215 



axis of X by a, we have 



d£ drj 



W cosB - — ; WsmB = -37; 

 at at 



dp dp 

 a G COS a = — — r- = -37 : 



« G sin a — — —r- = -3- . 



Substituting these values we shall have 



dp 

 —r = fx G W cos («-/?) + 



dp 

 dt 



Denote the angle between G and W by y and let d be the total 

 variation of the pressure at any point (expressed in millimeters per 

 hour) and d' the variation of the pressure, if the system is stationary, 

 we have 



dp 10333 1 



dt ' 760 3600 

 10333 1 



m- 



d 



,r 



(2) 



760 3600 



Substituting these values we shall have 



d = <5 + 0.0324 G W cos r (3) 



If the pressure at the movable origin is invariable we have 



and consequently 



d = 0.0324 G W cos r (4) 



At the front of a cyclone the angle y > tz and consequently d 

 is negative and the pressure decreases; at the rear y < n and the 

 pressure increases. 



Example. Let us consider a movable cyclone whose central 

 pressure is constant and whose velocity of propagation is so small 

 that we can consider the motion of the system as a geometrical 

 movement of the isobars ; finally we suppose that the radius of action 

 is so great and the maximum velocity so slight that we can apply the 

 same ratio between the gradient and the velocity as in rectilinear 



