of the fluctuations in solar activity. We will not discuss here how the 

 fluctuations in solar activity, which are hardly noticeable in the total 

 radiation from the sun received at sea-level, may be strongly reflected 

 in fluctuations of air-pressure as a consequence of motions induced in 

 the higher atmospheric layers where the ultra-violet radiation is absorbed 

 (B. Haurwitz). From a simple inspection of the Batavia air-pressure 

 cur\-e it is clear that air-pressure is depressed during years of many 

 sunspots and rises higher and oscillates more freely during years of few 

 sunspots. 



I think the situation in its general outlines is clear. The earth 

 possesses, like ever}^ oscillator, some fundamental period, perhaps it 

 even shows two, but certainly not many. The sun influences the motion 

 of this oscillator by its energy stream. The earth is like a violin, the sun 

 is the player, its radiation is the bow. And the reason why the resulting 

 music is not continuously the same tone is that the source of energy 

 fluctuates so that the music reminds one of numerous variations on the 

 same theme. 



I found by trial and error that the fluctuations of air-pressure at 

 Batavia can be reconstructed quite adequately by the application of the 

 following rules : — 



(1) A high- pressure year follows one, two, or three years after a 



sunspot minimum year. It appears whenever the sunspot 

 number of the year surpasses 20. It appears three years 

 after the previous high-pressure year, if 20 has not yet been 

 reached. When in the first case the mean sunspot number 

 surpasses 50, the impulse will be called strong. 



(2) The next high-pressure year follows three, four, five, or six years 



later. It follows three 5'ears later if the mean sunspot number 

 has not or not. yet reached 81 or when the previous impulse 

 was strong. It follows four, five, or six years later when the 

 sunspot maximum has passed and the mean sunspot number 

 has decreased below 81. 



(3) The next high-pressure year follows two or three years later, two 



years later whenever the mean sunspot number has decreased 

 below 54. 



(4) The next high-pressure year foUows two or three years later, 



two years later whenever the mean sunspot number has 

 decreased below 13. 

 There are three points towards which I draw special attention : — 



Firstly, as already noted by C. Braak, if the period of the oscillation 

 is really three years the fall of the barometer evidently takes 

 only one year, the rise, however, two years. This has been 

 taken into account. The cause probably is that the heating 

 of the south equatorial current when the big circulation is 

 weakened occurs rather quickly, whereas the cooling actually 

 requires the transport of polar water from great distances and 

 is therefore late in showing its ultimate effect. 



Secondh', between two maxima of air-pressure when separated by an 

 interval greater than three years a secondary maximum is 

 introduced. 



Thirdly, there are two instances in which two successive years both 

 show high pressure. The first instance is 1918-1919, rule 2 

 leaving the case dubious. The second instance is 1944-1945, 



