RECORD AND DISCUSSION OF FORCE OF WIND. 



75 



velocity in any resulting direction, divide by n, or the number of observations 

 during that period ; we then have 



n 



V,„=^, and V=.-. 



n u 



A particle of air which has left the place of observation at the commencement of 



the period — of a day, for instance — will- be found at its close in a direction 180 + <p, 



p 

 and at a distance of E miles, equal to a movement with an average velocity of 



n 



the length of the path described by the particle can be found by the summation of 

 all the vs (for each hour) during the period. 



The above development supposes that all particles of the air surrounding the 

 station equally participate in the general motion, or that all particles describe equal 

 and parallel paths. 



To admit nothing arbitrary in the reduction, no attempt has been made to inter- 

 polate values in those instances where occasional omissions occur in the hourly 

 abstract. 



The great variability in the direction and force of the aerial motion renders the 

 taking of mean values for short intervals unnecessary, and we can at once proceed 

 to the mean monthly values. 



For the convenience of reference, and in illustration of the method of reduction, 

 one of the monthly abstracts of the sum of the velocity numbers of each wind is 

 here inserted. Similar abstracts were made for each of the seventeen months 

 during which the observations continued. 



