RECORD AND DISCUSSION OP FORCE OF WIND. 



77 



By means of 2 11, and 2 R a for the respective periods, we find the following 

 mean directions : 



From the above results we see that, in general, the mean true direction of the 

 wind is from the eastward, varying in the several months to the northward and 

 southward of it. There is but one exception, namely : in the month of June, the 

 wind veers round to the westward of south. In spring and autumn, the resulting 

 true direction is almost exactly east, as well as for the whole year; in winter it is 

 E. N. E., and in summer S. E. by S. 



Average Velocity in the Mean Direction of the Wind. The average velocity in the 

 mean direction of the wind or, in other words, the mean velocity of the resulting 

 wind which is necessarily smaller than the mean velocity of the several winds on 

 account of the neutralization by opposing winds, is found by dividing the quantity 

 li by the actual number of observations (exclusive of calms). Thus, for September, 

 1853, we found R = 995, n the number of hours of observations = 348, hence 

 V= 2.9 miles per hour. In similar manner, Fhas been found for each month of 

 the year. In the table below, the quantities opposite the months from September 

 to January inclusive, are mean values derived from the years 1853 and 1854, and 

 1854 and 1855. 



Having found the resulting direction of the wind and its mean velocity in this 

 direction, we proceed to determine the mean velocity of each wind. 



