Xliv INTRODUCTION. 



thereto the number of times the wind has blown from each direction, which 

 is equivalent to considering the wind to have the same mean velocity for all 

 directions. 



If directions are observed to sixteen points, half the number belonging 

 to each extra point, should be added to the two octant points between 

 which it lies ; for example, NNE = 6 should be separated into A^= 3 and 

 NE — 3 ; ESE = 4 into E^i and SE = 2 . The result will be approximately 

 identical with that obtained by using the complete formula for sixteen points. 



Table 48. Mzdtiples of cos 45° ; form for computing the numerator and 

 denominator. 



Table 49. Values of the 7nean direction (a) or its complement (90° — a). . 



Table 48 gives products of cos 45° by numbers up to 209, together with 

 a form for the computation of the numerator and denominator, illustrated 

 by an example. The quadrant in which a lies is determined by the follow- 

 ing rule : 



When the numerator and denominator are positive, a lies between 

 iVand E. 



When the numerator is positive and the denominator negative, a lies 

 between 5" and E. 



When the numerator and denominator are negative, a lies between 

 6" and W. 



When the numerator is negative and the denominator positive, a lies 

 between A'' and W. 



Table 49 * combines the use of a division table and a table of natural 

 tangents. It enables the computer, with the numerator and denominator of 

 Ivambert's formula (computed from Table 48) as arguments, to take out 

 directly the mean wind direction a or its complement. 



The top argument consists of every fifth number from 10 to 200. 



The side argument is given for every imit from i to 50 and for every two 

 units from 50 to 150. Tabular values are given to the nearest whole degree. 



Rule for using the table : 



Enter the table with the larger number (either numerator or denomi- 

 nator) as the top argument. 



If the denominator be larger than the numerator, the table gives a. 



If the denominator be smaller than the numerator, the table gives 

 90° — a. 



a is measured from the meridian in the quadrant determined by the rule 

 given with Tcfble 48. 



*From Hand-book of Meteorological Tables. By H. A. Hazen. Washington, 1S88. 

 A corrected copy of the table has been kindly furnished for the present volume by 

 the author. 



