ROTATION AND ATMOSPHERIC DISTURBANCES GORODENSKV I09 



generally turns in a direction contrary to the motion of the hands 

 of a watch when an area of low pressure is passing by the station. 

 In fact by employing the observations of stations for which Dove's 

 law holds good we obtain a coefficient greater than it ought to be 

 by a quantity independent of the velocity of the wind. This inter- 

 esting phenomenon is shown with perfect clearness in the graphical 

 representation. 



As the function // v characterizes the friction of the air in a direc- 

 tion perpendicular to the current, one ought to be able to determine 

 this function theoretically, if we knew a similar function for the 

 direction parallel to the current, since the two coefficients ought to 

 depend directly on each other. 



During the progressive motion of masses of air a certain friction 

 is developed whose reaction, tending to reduce the linear velocity 

 of the movement, is perpendicular to this velocity, according to 

 the simple law of Guldberg and Mohn / = tj v where /is the reaction 

 of the friction, v is the velocity of this wind and tj is a coefficient 

 that depends only on the pysical state of the air and the surface of 

 the earth. 



This being recognized, we have studied a regular stationary 

 cyclone of large extent and without any progressive movement, 

 from a purely mechanical point of view. After having examined a 

 portion of this whirlwind somewhat distant from its axis we have 

 obtained the following expression for the function (vpi) viz: 



1 1 



- = -7 + 1 (7) 



H sir 



where 



sin a cos a 



£ = ~T7 : — 1? s (8) 



J (r) sin a — K cos a) 



The letters introduced into these formulae have the following 

 signification : a is the angle formed by the direction of the current 

 of air with the radius vector R drawn to the axis of the whirlwind 

 and is counted positively starting in the direction of the motion of 

 the hands of a watch from some initial radius vector; / indicates 

 the product v R which I have called the expression of the intensity 

 of any atmospheric disturbance ; K is given, as already stated, by 



4;r 

 K = T sin a (9) 



