SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. <l 



Assume the radius of action of these cyclones to be about 20 and 

 that at this distance the absolute pressure is 76o mm . The pressure 

 b at the center is then in the first cyclone 72 2.i3 mm and in the second 

 724.4o mm , and the increase of the pressure at the center is 2.27 mm 

 at the same time that the maximum velocity has diminished i m 

 from 20.0 to 19.0. Adding b to b — b we shall find the pressure b 

 and consequently we calculate the increase of pressure at each dis- 

 tance r. Assuming that the change has taken place in 4 hours, we 

 find the hourly variation d by dividing the increments by 4 as 

 follows; 



FIG. 39 



By constructing a curve repre- 

 senting d = f (r) we easily deter- 

 mine the distance r for successive 

 values of d and can construct 

 the curve of equal variation (see 



%• 39)- 



(2) Moving cyclone with pressure 



constant at its center. 



When the pressure at the mov- 

 ing center remains constant, the 

 variation of the pressure at any 

 fixed station is determined by equa- 

 tion (4) of §30 and we have 



d = 0.0324 G W cos y 



