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368 M. Melloni on Dew. 



>di motf T __ . 'iLca'i fliw aonornoo 



Irani 0/ X^w in rolynesvi. 



A curious fact, and one not much known, which seems at 

 first sight to contradict what we have been saying, is the 

 extreme feebleness, or the absolute non-existence of dew in 

 that extensive assemblage of small islands in the torrid zone, 

 generally fertile, and more or less rich in plants, which geo- 

 graphers denominate Polynesia. 



But, with a little attention, it will soon be seen that this 



apparent anomaly affords one of the most striking confirma- 

 tions of the truth of the theoretical views unfolded in the 

 course of this memoir. In fact, whatever may be the hu- 

 midity of these small islands, scattered here and there in tlie 

 vast ocean like oases in a desert, and their tendency to the 

 cooling produced by the long nights and luxuriant vegeta- 

 tion, the small extent of their territories renders the atmo- 

 spheric column superincumbent on each of them easily per- 

 meable even to its centre by the air of the surrounding sea. 

 This invasion is, moreover, favoured by the trade-winds 

 which prevail constantly in those latitudes. Now we know 

 that the air in the midst of vast seas preserves a nearly 

 uniform temperature. The stratum of air cooled by the 

 contact of the soil will then be warmed by mixing with the 

 air which is constantly reaching it from the sea, and the 

 difference between the temperatures of the day and night 

 being extremely small, dew can scarcely be formed at all, or, 

 at any rate, in very slight quantity. 



>:jbfIUOTIJJB 



Want of Dew on Ships traversing the vast solitudes of the Ocean. 



Perfectly analogous causes prevent the formation of dew 

 on ships which traverse the vast solitudes of the ocean. But, 

 what is truly singular, is the appearance of the phenomenon 

 on board these same ships on arriving afterwards in the 

 neighbourhood of terra firma. Thus the navigators who 

 proceed from the Straits of Sunda to the Coromandel Coast, 

 know that they are near the end of their voyage when they 

 perceive the ropes, sails, and other objects, placed on the 

 deck, become moistened with dew during the night (Le Gentil, 



