430 THEORIES RESPECTING THE NIGER, 
begin early in June. Accordingly the Nile in 
Egypt, where it is nearly at the same distance 
from the limit of the northern tropic as the Congo 
in the higher part of its known course, begins to 
swell about the 17th of June. Neither it, indeed, 
nor the Niger in Wangara, overflows its banks, 
and inundates the country, till August ; but this 
inundation is only the crisis of that constant ad- 
ditional influx of waters which has been taking 
place for a considerable time. According to this 
analogy, the Congo ought to swell nearly about 
the same time with the Nile, or before the end 
of June. In fact, however, it does not swell till 
nearly two months and a half later. A cause for 
this retardation is sought in the hypothesis of a 
large lake, situated near the limit of the tropic, 
which receives the waters of the Niger and its 
tributaries, and transmits them to the Congo. 
It would appear, however, that when the feeders 
of this lake are augmented, it ought, in a very 
short time, to experience a sensible rise, and 
must then communicate a greater or less increase 
to any river which flows out of it. It does not 
appear, therefore, that the hypothesis of one lake 
is sufficient ; but the case may be different in re- 
spect to a chain of lakes successively breaking 
the force of the original current ; and report cer- 
tainly speaks strongly to the existence of such 
a chain. It is difficult to estimate the precise 
