2l8 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 51 



For example assume 



T t - T, - 2° 



we have W about 3™. 



In cyclones of the temperate zones the radius r is generally so 

 great that we can approximately calculate the ratio t/ : G by the 

 formulae deduced for rectilinear isobars. In this case the quantity 



U 

 2.78 pr cos (p depends on the latitude S and on the coefficient of 



^0 

 friction k. Denoting this quantity by B we have 



W = B 



The value of 5 is given in the following table: 



FIG. 34 



to a c and 6 / parallel to a c. 



As to the direction of the pro- 

 pagation of a barometric mini- 

 mum that depends on the tra- 

 jectory of the alimentary air. Let 

 c c' in fig. 34 be the direction of 

 the velocity of propagation W; 

 the barometric minimum moves 

 from c to c' in an infinitely short 

 time d t; at the same time a par- 

 ticle of alimentary air moves from 

 a to a' with the velocity U. Draw 

 c b parallel to c' a! '; a' b parallel 

 to c c', a'd and b e perpendicular 



