CLIMATE AND PREVALENT WINDS 211 



finally vanishing as they pass over one of the larger land 

 masses. The opposite phenomenon also occurs, and clouds 

 are formed over the lagoon by the extra evaporation from its 

 surface ; these are the clouds that, on calm fine days, are 

 noticed by the sailor to stand poised above atolls. The lagoon 

 is shallow, and is hotter than the ocean water ; there is a 

 tremendous evaporation going on from all over its surface, 

 and the water vapour is swept upwards in the rising column 

 of hot air till, meeting with the colder layers above, it con- 

 denses and forms the private sky of the lagoon. The island 

 ring is in fact the one and only radiating object in the midst 

 of the ocean, but since it is really a sponge work it can never 

 rapidly cool at night, because of the great warm-water jacket 

 which surrounds and permeates it ; the consequence is that 

 the deposition of dew is a very rare phenomenon indeed. 

 A curious state of things is therefore brought about in the 

 physical conditions of the islands, for the excessive radiation 

 from the heated surface prevents the fall of rain, and yet the 

 night fall of temperature of the surface of the land cannot 

 become so great that dew can be deposited. There is then no 

 compensation here, but only a vicious circle of overheated coral 

 and cleft rain-clouds, without the accompanying blessing of dew. 



The result of dry weather when prolonged is accordingly 

 severe and the vegetation suffers ; the undergrowth fades and 

 becomes parched and brown ; the leaves fall from the trees, and 

 the coconuts drop prematurely, leaving the islands very bare 

 and waste. It is the opinion of the Clunies-Ross family that, 

 despite the increased planting of coconut palms, these dry 

 periods are becoming more frequent and more prolonged ; 

 though strange to say the wells on Pulu Selma never become 

 exhausted, despite there being no restriction placed on water 

 using. 



Thunder and lightning are very rare, and when observed 

 the phenomenon is usually far distant ; storms other than 

 cyclones play no part in the history of the islands, for the 

 absence of large areas of land to undergo rapid heating and 

 cooling saves them from sudden atmospheric variations. 



