2l6 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 5 I 



motion. At the station A (see fig. 32) we observe the velocity 

 U t — 1 2 m and the variation of pressure^ = — o.5 mm ; at the sta- 

 tion B we observe U 2 = 8 m and d 2 = — 0.4 mm . Assume the mean 

 latitude equal to 6o° and the coefficient of friction k = 0.00006, 

 we shall have (see §9) the normal angle a = 64°.6 and the normal 

 ratio G : U = 0.15. From equation (4) by substituting c7, = i.8 mm 

 and G 2 = i.2 mm , we shall find W t cos y x = — 8.6 m 

 and W 2 cos y = 10. 3 m . 



FIG. 32 



Let A U 1 and B U 2 (fig. 32) be the directions of the veloci- 

 ties, that is to say, the true directions of the currents of air, 

 which are different from the direction observed by wind vanes, 

 because of the different values of the friction in the midst of the 

 current of air and at the surface of the earth (see §34). Draw the 

 angles U l A C = U 2 B C = a then the point of intersection C is 

 the movable origin or the location of the barometric minimum. 

 Lay off C a = W cos 7-, and C b = W cos y 2 and construct a circle 

 through the three points a, b and C then the diameter C d represents 

 the velocity of propagation W both in direction and in extent. 



