RECORD AND DISCUSSION OF FORCE OF WIND. 



77 



By means of 2 R, and 2 i?«, for the respective periods, we find the following 

 mean directions : — 



Macrnetic ?. 



True f . 



True direction. 



Winter (December, January, February) 

 Spring (March, April, May) . 

 Summer (June, July, August) 

 Autumn (September, October, November) 



Year . 



351° 

 21 

 72 

 22 

 19 



243° 



273 



324 



274 



271 



E. 27° N. 

 E. 3 S. 

 E. 54 S. 

 E. 4 S. 



E. 1 S. 



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 VehcHij in the Mean Direction of the Wind.—ThQ 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 72 = 995, n the number of hours of observations = 348, hence 

 7=2.9 miles per hour. In similar manner, 7 has 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. 



Table of the Mean Velocity of the Resulting Wind. 



Month. 



R 



September 

 October . 

 November 

 December 

 January . 

 February 



1637 

 1892 

 1016 

 1633 

 694 

 1823 



Month. 



R 



541 

 1559 

 1136 

 1390 

 1097 



783 



262 

 385 

 441 

 257 

 200 

 244 



2.1 

 4.0 

 2.6 

 5.4 

 5.5 

 3.2 



Average Ffor the whole year 



4.5 miles per hour. 



Having found the resulting direction of the wind an 

 direction, we proceed to determine the mean velocity of ea.-h wind. 



d its mean velocit}- in this 



