m 



because these are usually associated with feeble wind forces, so 

 that the direction becomes uncertain. 



It appears however from the large frequencies for o = 45° and 

 N and NW directions of the gradient (208 and 180), greater than 

 any other, that the omission of smaller values of a in these cases 

 certainly gives too great a value for the average angle of deviation, 

 whereas for E and SE directions of the gradient the influence of 

 smaller values than 45° are compensated by tiiose greater than 90°. 

 The results of this inquiry are therefore to be considered as doubtful, 

 not only in an absolute but also in a relative sense. 



A more serious objection against this method is that it appears 

 from table I that tlie meteorological field is by no means to be 

 taken as uniform : easterly and south-easterly gradients are generally 

 associated with wind forces and angles of deviation considerably 

 greater than northerly and north-westerly directed gradients. The 

 frequencies indicate that a gradient of a given magnitude and direction 

 may be accompanied by different forces and angles of deviation so 

 that the gradient, calculated as a iv>u/taii( difference of pi'essure in 

 a central point and four circumjacent stations cannot be considered 

 as a reliable measure of the wind. A positive difference in a given 

 direction does not exercise the same influence as a negative difference 

 in the opposite direction. If, therefore, we wish to investigate this 

 relation, the computation of a resultant must be avoided and each 

 direction is to be taken into account with its proper coefficient of 

 influence. 



2. To this purpose dijferences of atmospheric pressure between 

 Flushing on the one hand and Valencia, Biarritz, Munich, Neufahr- 

 wasser and Lerwick in tiie other hand are associated with the wind 

 at the first named station, as published in the annals of the K. N. 

 M. Institute for each day of the eight months; January, February, 

 December 1912 and 1913, and January, February 1914. The average 

 differences for the whole period are : 



1. Flushing — Valencia +5.8 mm. 



2. „ —Biarritz —1.9 



3. „ —Munich —4.3 



4. ,, — Neufahrwasser -J" '^■'^ 



5. „ —Lerwick -f 7.9. 



The average wind at Flushing during the same period is: 



3.70 m.p.s. S 25°36' W 



Wn = — 3.34 N component 



We := — 1.60 E component. 



