lo6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



Let us imagine an elementary small mass projected horizontally 

 on a perfectly polished plane surface with an initial velocity v . 

 It continues along its route with this same velocity tracing a curved 

 line whose radius of curvature, as is well known, is given by the 

 equation 



47r • ft\ 



sin a (1) 



T 



where T is the duration of a complete day, i. e., one rotation of the 

 earth and a the latitude of any place on the earth traversed by 

 the center of the mass. The center of curvature of the path is 

 always on the left-hand of the direction of motion where the mass 

 is in the southern hemisphere and on the right-hand in the north- 

 ern hemisphere. 



Assume the notation 



4tt 

 K = „ sin a 



which expresses the angular velocity of the moving point. Its 

 value can be calculated from observation of the wind between two 

 stations in the following manner: 



At the station A take an observation of the velocity of the wind 

 blowing towards the station B. The distance between the stations 

 and the velocity of the wind being known we obtain by simple divi- 

 sion the interval of time required by the particle of air to reach the 

 station B. By observing at this moment the direction of the wind 

 (at B) we find a difference between the two observed directions, 

 which difference should give us the required value K. This value 

 generally differs greatly from that calculated by the theoretical 

 formula because of the many accidental conditions, among which 

 there is however one force that constantly and continuously influ- 

 ences the movements of the atmosphere. This is the internal fric- 

 tion (or viscosity) of the air and also the friction between the air 

 and the surface of the terrestrial globe. If the number of observa- 

 tions employed by us is sufficiently large, as well as the length of 

 the period of time and the number of stations collated, then all 

 anomalies neutralize each other and one obtains a resulting mean 

 value for K as diminished by friction only, or k = fx K 

 Now it is the coefficient n that is the desired characteristic of the 

 air near the ground. 



