478 SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



Our table of corresponding tbeoretical values of Fand d gives for the 

 latitude of Cbristiania, or GO^ north, the constant product 7 5 = 37.5, 

 whence 80F(? = 3000. Mr. Mohn gives as the result of observations on 

 the force of the wind in Norway the mean product 80 F5 = 14G0; that 

 is to say, very nearly one-half of our theoretical result. It is easy to 

 recognize the reason of the apparent discordance of these two results. 

 Mohn, in the passage that we have cited, says that "upon the sea the 

 force of the wind will be, for the same gradient, far greater than in the 

 interior of the country." 



It is, on the other hand, certain, according to all the observations 

 made both on mountains and in balloons, that the force of the wind 

 increases considerably as we ascend in the atmosphere. And these facts 

 relative to atmospheric currents conform entirely to that which has been 

 established for liquid currents : the velocity at the base or near the 

 borders is notably feebler than the mean velocity of the current. 



There is, then, no reason for surprise that the velocities observed by 

 Mohn at the surface of the earth are feebler than the velocities deduced 

 from our theoretical formula, which should give us the mean velocities 

 of the atmospheric currents. The figures that he cites show that, in 

 order to pass from the latter to the former or from the theoretical to the 

 observed velocities, it is necessary to apply a coefiQcient of reduction, 

 which is 0.40 for the smaller velocities, and which, increasing in pro- 

 portion as the velocity increases, can become 0.60 for the very greatest 

 velocities. 



