144 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 51 



The ratio between the velocity and the gradient is found by equa 

 tion (i) 



v fi cos a 



pk 



(4) 



By formulae (3) and (4) we can determine the direction and the 

 velocity of the wind : by graphical construction we find their values 

 in the following manner. 



Let B, fig. 3, be the direction of the gradient and let two dis- 

 tances O B and O A be in the ratio. 



OB :0 A = 2<o : k 



Describe a circle with the radius O B and erect A L perpendicular 

 to O A : making the arc B D equal to the latitude and draw D N 

 parallel to B O; we shall have the angle A O N = a. Describe a 



f 



semicircle with the diameter C = — and the chord O M will be 



p k 



equal to the velocity v. 



We shall call the angle a, determined by equation (3), the normal 



angle of inclination. 



The relation between the velocity and the gradient depends on 

 the density of the air. Supposing the temperature to be o° and the 

 pressure 76o mm the density p is 



6' 

 £45° 



1.29305 

 9.8089 



= 0.13184 



