1325 



assumed to be possible, that over large areas slow rising or sinking 

 of air takes place, which is quite compatible witii the stratitied 

 structure of the stratosphere. 



Sinking is likely to occur, because the air flowing in from higher 

 latitudes comes in from colder regions and will thus be cooled 

 strongly and become denser. 



It might also be possible that the vertical component of rotational 

 deviating-force, which is downward for eastern winds and reaches 

 a maximum (2 to v) at the equator, favours sinking of air, 



Krakatoa-wind. It is my opinion that this wind in the first place 

 should be regarded as a stationary aircurrent. Arguments in favour 

 of this assumption are, first the observation made in 1883 that the 

 Krakatoa ashes were carried seven times round the globe with a 

 pretty constant velocity of ± 40 m.p. sec, secondly that at Batavia 

 twice (once in March and once in September) at the same height 

 of about 30 km. an Eastwind of equal velocity was observed. 



The current being stationary it will run parallel to the isobars, 

 hence the latter will possess a meridionall}' directed gradieut. The 

 amount of this gradient may be calculated with the aid of the 

 formula ') 



h 7' 

 A 5=0157 '-vsinw'). 



Assuming in latitude 6° — - to be — -, To = 223° and v = 40, the 



formula gives AB = 0.005 mm. 



The same calculation may be made for the trade in the bottom- 

 layers. 



In this case for v may be taken the mean velocity v=: 10 m. p. s. 

 observed at the lighthouse "de Bril" (situated in midsea S. of Celebes 

 latit. — 6°). The formula gives A/i = 0.17mm., fairly agreeing with 

 the amount 0.20 borrowed from Braak's isobaric chart. 



However in this case the application of the formula is restricted 

 as AB should become zero at the equator, which does not happen. 

 Indeed we see there the trade not paralleling the isobars, but to be 

 directed perpendicularly to them. 



Regarding the Krakatoa-wind presumably the gradient disappears 

 and changes sign at the equator and the following calculation shows 

 how the alleged pressure-differences corroborate with this conjecture. 



For the pressure difference at 25 km. height between latitudes 

 6° and 30° has been found 2.7 mm., or a gradient 0.11. If this 



1) Hann, Lehrb. d. Met. 1915, p. 488. 



91 

 Proceedings Royal Acad. Amsterdam. Vol. XX. 



