MOVEMENTS OF ATMOSPHERE GULDBERG AND MOHN 223 



Assume that W, the velocity of propagation of the center, is con- 

 stant. For the value y = 71/2 we have d = o, that is to say, the 

 curve of no variation is a straight line that passes through the center, 

 and is perpendicular to the direction of propagation of the center. 



Assuming y = o and y = n, and also G = G Q we obtain the maxi- 

 mum value of d, which consequently falls at two points at the dis- 

 tance r from the center along the trajectory of the cyclone. 



The curves of equal variation are determined in general by the 

 equation 



G cos y = constant. 



We can easily construct these curves by the aid of the curve of 

 the gradient. 



In the interior portion, we have the equation 



G = G x r 



and the curves of equal variation assume the form 



rcos;- = constant. 



These curves are straight lines perpendicular to the direction of 

 propagation. 



By using the values of G given in the preceding table we have 

 constructed, for every o.2 mm , the curves of fig. 40, assuming W = 

 io m . 



If we wish to construct curves of equal variation of pressure for 

 any date whatever, we can construct two systems of isobars ap- 

 propriate to the given date, and then determine graphically the 

 curves of equal variation. It is evident that by choosing two appro- 

 priate dates so far apart that the distance between the centers 

 exceeds the diameter of action, 2 r, the curves of equal variation 

 and the isobars themselves become identical and the maximum 

 variations are the centers of the two systems of isobars. 



(3) Moving cyclone with variable pressure at the center. 



When the pressure at the center varies, the variation of pressure 

 is determined by equation (3) of §30 and we have 



*=• d + 0.0324 G W cos y 



The variation d which is a function of r, is determined as we have 

 shown in the first case where the system is stationary. Assuming 

 W = io m and introducing the values of G and of d given in the 

 preceding table for the first case, we shall find d as follows: 



