1315 



(iij Oct. 1916 on (he "Duizend Elilaiideji" aiui in June July 1917 

 at Bandoeng resp. 84 km. to the N. and 119 km. to the S.W. of 

 Batavia) only a small number has been added to the material for 

 the levels above 10 km. 



Table I shows the nnmber of observations for each month of the 

 year. 



For an earlier publication certain functions of windvalnes for 

 five seasons, specially chosen for that purpose, have been compiled 

 by me. These functions gave a synopsis of direction, velocity and 

 frequency and were called relative directional-velocities. Moreover 

 I gave the resultant directions and velocities obtained by simply 

 averaging the rectangular components of the observed windvectors. 



On this occasion the average values of the components have been 

 compiled for the different months of the year separately. 



To apply this working-system is rendered possible by the constancy 

 exhibited by the direction of aircurrents above Batavia, even when, 

 as is the case for some months, the number of observations is scarce 

 for the higher layers. Above the 10 km. level, however, this number 

 decreases so quickly, that it was indispensable to try getting plausible 

 valnes of the mean components by the process of graphical 

 averaging. 



For this pnrpose two isopleth-diagrams have been drawn np, one 

 for the east west, the other for the northsouth components. F'rom 

 these graphs fresh monthly values have been taken for the different 

 levels and from them new vectors have l^een computed. These vectors 

 have been united in table II. 



They may be considered to give direction and velocity of the main 

 aircurrent for each month and level. 



In this table II are framed and typed in different colours 1. 

 easterly winds having a southern component; 2. those having a 

 northern one, 3. westerly winds with components either to the south 

 or to the north. By this the table gives a synopsis of- the vertical 

 extensions of the principal aircurrents in the different months through- 

 out the year, which may be described in the following way. 



Tradewind. It is a well-known fact that in the southerly winter 

 the tradewind blows over the seas surrounding Java as an easterly 

 wind with soutliern components. However, the application of the 

 correction for the diurnal and semidiurnal variation mentioned above 

 on the average windvectors under the 3 km. level, has resulted in 

 east- winds with northern components. 



This outcome is a consequence of the fact, that by day the suction 



