202 CORAL AND ATOLLS 



small and comparatively sparsely vegetated island, and that 

 as a consequence, tlie rainfall, as registered for this island, 

 probably does not represent truly the rainfall of the group as 

 a Avhole. During those months in which the minimum rain- 

 fall is registered by the Pulu Tikus instrument, rain, in some 

 considerable quantities, falls on Pulu Atas and Pulu Panjang. 

 Were the records to be taken on these larger pieces of land, 

 which lie six miles away, I think there is no doubt that the 

 annual rpJnfall would have a higher index, and at the same 

 time be more uniform throughout the course of the year. 



That these meteorological records help in the under- 

 standing of the scant, but interesting, fauna and flora is only 

 natural ; for every living thing must reach the islands as a 

 chance plaything of the winds or waves ; but since the true 

 explanation of the origin of atolls lies in the appreciation of 

 the physical forces with which they are surrounded, they should 

 help, if rightly interpreted, in understanding the method of 

 island building. For this reason it is very fortunate that so 

 accurate a set of observations is available, for the details of 

 the climatic conditions of the group which have hitherto been 

 published do not give a satisfactory working basis. 



The Prevalent Winds. — The prevailing winds are the 

 S.E. and the E.S.E. which constitute the Trade winds. The 

 normal variation of the Trades includes winds blowing from 

 the S.E., E.S.E., and E., and the winds from these quarters 

 blow on an average for 300 days in every year. It must not 

 be thought, however, that the odd 65 days are consecutive 

 days occupied by any change of the Trades, for as a matter of 

 fact the 300 days are very equally distributed over the twelve 

 months. 



The wind blows from the S.E., E.S.E., or E. as follows, the 

 numbers being averaged from the records of four years : 



IN 



Jan. 23 days Feb. 18 days March 23 days April 23 days 



May. 23 „ June 26 „ July 27 „ Aug. 27 „ 



Sept. 27 „ Oct. 28 „ Nov. 28 „ Dec. 27 „ 



