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Meteorology. "The treatment of wind-observations" By 



Dr. J. P. van der Stok. 



(Communicated in the meeting of February 23, 1907). 



1. When working out wind-observations we directly meet with 

 the difficulty that a method holding generally, in which the charac- 

 teristics of a wind distribution come to the fore in condensed 

 form, does not exist. The discussion held for many a year concerning 

 the desirability or not of an application of Lambert's formula, i. e. 

 of the calculation of the vectorial mean of velocity or force has not 

 led to a definite result and the consequence is that for regions where 

 trade- and monsoon winds prevail the calculation of this mean can 

 be applied, not for higher latitudes, so that here we have to judge 

 by extensive tables of frequencies of direction and mean velocities, 

 independent of direction. 



When working out the wind-observations made at Batavia I did not 

 hesitate to make an extensive use of this formula; the same method has 

 been followed in the atlas for the East Indian Archipelago; but in order 

 to give at least a notion of the value of the velocities annulling each 

 other here I have added to the resulting movement (called by Hann 

 windpath) a so-called factor of stability. If namely the wind were 

 perfectly stable, the vectorial mean would be equal to the mean 

 independent of the direction and the stability would amount to 

 'JOOVo, which percentage becomes smaller and smaller according to 

 the direction of the wind becoming more variable. So here attention 

 is drawn to the fact, that a part of the observations is eliminated, 

 but it is not indicated what character this vanishing part has which 

 becomes chief in our regions. 



In the climatological atlas lately published of British India the 

 same method is followed ; in the "Klima Tabeller for Norge" Mohn 

 gives but the above mentioned tables without calculation of the 

 vectorial mean, which is, indeed, of slight importance for this climate. 



The same uncertainty is found in the graphical representation of 

 a wind distribution by so-called windroses; almost everyone who 

 has been occupied in arranging books of prints has projected wind- 

 roses of his own ; some of those roses, as e. g. in the "Vierteljahrs- 

 karte fiir die Nordsee und Ostsee" published by the "Deutsche 

 Seew T arte", show only the frequencies of direction without velocities; 

 in others, as e. g. those shown in the above atlas of the East Indies, 

 each direction is taken into account with the velocity belonging to it 

 as weight, so that mean velocities are represented. All these roses 



