MOVEMENTS OF ATMOSPHERE GULDBERG AND MOHN 163 



Applying these formulae to the central (descending) region sit- 

 uated between the center and r = 1.5 and by graphic interpolation 

 beyond, we find the following values: 



By these formulas and examples we see that for a given latitude 

 and a given coefficient of friction the whole system of a whirlwind 

 is determined by the maximum velocity and the distance from the 

 center of the movement of the point where that velocity is found. 



Chapter III 



THE PERMANENT VERTICAL CURRENTS OF AIR 



§15. Rectilinear movement 



We consider a particle of air moving in the direction of the vertical 

 axis of z which we suppose positive upward. We neglect the action 

 of the rotation of the earth and the viscosity or resistance between 

 the molecules of air. Then we have three forces, namely: the 

 force produced by the variation of the pressure 



1 dp 



p d z' 



the force of the weight g, and the tangential force 



dw 

 d z 



where w represents the vertical velocity. 



The equilibrium between these three forces is given by 



1 dp dw 



--JT = -g-W--j (1) 



p dz dz 



Expressing by p and w the values of p and of w at any point, the 

 equation of continuity becomes 



p w = p w (2) 



This equation demands that the section of the current be of con- 

 stant area. The above equations hold good for ascending move- 



