176 COMPENDIUM OF GEOGRAPHY AND TRAVEL 



Kampar, Kakan, and Indragiri, all of which form vast 

 deltas with labyrinthine intersecting channels at their 

 mouths. Upon the western side of the island the only 

 river of importance is the Singkel, which debouches 

 opposite Banyak Island, and is navigable for a consider- 

 able distance by small vessels. 



4. Climate and Heterology. 



Sumatra differs considerably in its climate and rain- 

 fall from Java. In the latter country — at all events in 

 its eastern portion — a strong S.E. monsoon blows from 

 March to November, which produces a marked degree of 

 aridity, causing trees to shed their leaves and filling the 

 air with powdery dust. This dry season, produced by 

 the winds sweeping over the parched and heated deserts 

 of the Australian continent, becomes less and less marked 

 as we increase our distance from the latter country, until 

 at the Straits of Sunda it becomes almost non-existent. 

 The position of Sumatra, bisected as it is by the equator, 

 causes the winds and seasons of Ache to differ from 

 those of the Lampongs at the southern extremity. For 

 at the north the monsoons blow from the north-east and 

 south-west ; in the centre is a wide belt of variable 

 winds with alternating calms and squalls ; and in the 

 south the monsoons blow from the south-east and north- 

 west. A series of observations at Palembang show that 

 from November to March the prevalent winds are westerly 

 and north-westerly, this being the regular rainy season. 

 April is the month of the change of the monsoons, when 

 thunderstorms are most frequent. From May till Sep- 

 tember easterly and south-easterly winds prevail, and the 

 " kentering," or change of the monsoon, comes in September 

 or October. During the shiftino- months of the S.E. 



