UNPEECEDENTED FLOODS. 
325 
hav^ reported,, like myself, famine to exist in different tropical dis- 
tricts. This calamity, as realized by Mussaad, was occasioned by a 
state of warfare ; but, as a rule, I know that during the length 
and breadth of the Soudan it is caused by periodical shortcomings 
of rain, so that whole districts are famished, and the peoples are 
driven to migrate, or support themselves upon grass-seeds and 
fruits, that require less moisture to bring them to maturity than 
the grain crops, upon which the populations principally depend for 
support. 
We all know that in the tropics the rainfall is very different to 
what it is in this country or any part of Europe. The land rain, or 
well -sustained continued days, and even weeks, of rain experienced 
in Europe, is unknown in the tropics, where, on the contrary, the 
torrents that fall may be reckoned by hours, and but exceptionally 
by entire days of duration. They are generally, I may almost say 
invariably, the outburst of heavy storms of thunder and lightning ; 
and throughout the tropics it is well known their frequency is 
uncertain, and of much oftener recurrence in one district than 
another; hence, whilst the one is flooded, the other may be so 
parched as to preclude the growth of grain. 
The White Nile, and the district we were returning from, has 
been reported, during the memory of man, never to have been so 
flooded, and to account for the low state of the Bahar il Gazal, I 
am naturally led to conjecture, that its supply of water from its 
western tributaries, by unprecedented drouth and perhaps increased 
evaporation, owing to a necessarily increased amount of heat, may 
have been thus unusually curtailed. 
Would this example not lead to the inference that other lakes— 
for instance, the Nyanzas — may occasionally prove to be subject to 
the same influences, and be found, in lieu of containing the enor- 
