458 
On the other hand we clearly perceive a variation of the corre- 
lation with the geographical longitude and latitude and with the 
season. Leaving aside for the present the western part of the archi- 
pelago north of the equator, we find in the remaining part in the 
East monsoon with a few unimportant exceptions negative correla- 
tion, increasing in amount from West to East. In the West monsoon 
the negative sign still prevails in the East, in the West however the 
positive sign appears almost without exception, so that there a surplus 
of rain falls during the barometric maximum. 
The explanation suggests itself that this change of sign of the 
correlation depends on the wind, which has also opposite directions 
in both monsoons. Now the relation between the barometric changes 
and the force of the monsoons is such that during the maximum of 
atmospheric pressure (caused by the relatively large amplitude of the 
barometric oscillation over Australia) the wind is reinforced during 
the East monsoon and weakened during the West monsoon, while 
at the minimum the opposite occurs’). From this we conclude that 
strengthening of the monsoon, either East or West, impedes the for- 
mation of rain. This phenomenon must be partly ascribed to the 
development of fewer local showers when a stronger wind prevails, 
partly, especially in the East monsoon, but perhaps also in the West, 
to the circumstance that the air, when it moves ina quicker current, 
remains a shorter time above the sea. 
The stronger negative correlation in the East would indicate that 
here, besides the influence mentioned above, still another factor 
makes itself felt, as well in the West as in the East monsoon. 
Very likely we have here a more direct influence of the neighbour- 
ing active centre in North Australia, causing drought during the 
maximum by falling air-currents, rain during the minimum by rising 
currents. 
Though the variation of the correlation finds in this way a natural 
explanation for the greater part of the Archipelago, the matter is 
less simple for the remaining North-western part. There, as in Java, 
the correlation is, generally speaking, opposite for both monsoons, 
but it is negative when Java has a positive correlation and vice versa. 
It is possible that the Barisan range, which in the northern part 
of Sumatra lies straight across the path of the monsoon, makes its 
influence felt. Also another explanation can however be given. 
While during the maximum the influence of Australia increases 
the pressure difference in other places, it is quite possible that here 
1) Cf. Natuurk. Tijdschrift voor Ned. Indië, Vol. LXX, p. 105. 
