with Geographic Botany. — Humidity. 



327 



termined whether the day was to be spent in the valleys to 

 leeward or to windward. But even in this group the islands 

 have peculiarities confined to each ; though rain had been 

 rare on the above island, Oahu, on visiting shortly after the 

 island of Taui, w^e learnt that for the last six months, in one 

 part of it, not a single day had occurred without some rain. 

 In all of the islands the vegetation is rich and fascinating, but 

 the portion of Taui subject to such plentiful rains surpasses 

 the others. 



Another instance of the rare occurrence of rain is men- 

 tioned by Sir Francis Head as taking place at Uspallata, but 

 is not to be easily accounted for. Uspallata is famed for its 

 silver-mines, and is also the last inhabited station on the 

 eastern side of the Cordilleras, on the Mendoza road ; around 

 is nothing but desolation and barrenness ; those who have 

 lived there never saw rain, and other facts are mentioned 

 showing its usual absence. 



Notwithstanding these illustrations, the fall of rain in most 

 countries has a relation to the latitude, and decreases in 

 amount as we recede from the equator. The manner in which 

 this occurs will be best seen in a tabular form. 



