NO. 17.] 



WIND. 



307 



What we may call gales, or wind-velocities above 15 metres per second, 

 are relatively very rare. Their distribution is as follows. 



The frequency of stronger winds has its minimum at 4 a. m., and its 

 maximum at 4 p. m. It is below the mean from 9 p. m. to 11 a. m., and 

 above the mean from 11 a. m. to 9 p. m. PI. I (v ;> 15 m. p. s. 1 mm. 

 = 1 case). 



Taking the totals of Calms in the Tables on p. 256 to 267, for each 

 hour of observation, smoothing them by the formula on p. 291, and dividing 

 them by 3 (September 2), we obtain the following Table, showing the mean 

 number of cases observed, and the diurnal period of the frequency of calms. 



