INTRODUCTION. XIX 
wu proof that it is influenced by the tropical rains, and 
that one branch of it, at least, must pass through some 
portion of the northern hemisphere. 
Another objection has been made to the identity of the 
Niger and the Zaire, grounded on the circumstance of no 
traces being discovered of the Mahomedan doctrines or 
institutions on the coast where the latter terminates. It 
would be a sufficient answer to observe, that as far as our 
present knowledge extends, the Niger, in Northern Africa, 
formed the boundary of Mahomedan invasion. What the 
difficulties may have been, whether moral or physical, or 
both, ‘* to impede the spirit of enterprise and proselytism 
which belongs to the Mahomedan character,” it would be 
idle to conjecture; but that they have been impeded, and 
in a great measure limited to the parallel of the Niger while 
on its eastern course, is pretty certain ; yet there appears to 
be neither difficulty nor want of means in crossing this 
river, though there may be both in descending it. Inde- 
pendently of the lakes and swamps, the sand-banks 
and rapids, that may occur, the Africans have not at 
any time, or in any part of the country, been famous for 
river navigation. But it is far from improbable, that 
Arab priests or traders may have penetrated into south- 
ern Africa; on the eastern coasts they held, at one 
time, powerful settlements, and Arabic words occur in 
all the languages of the negroes even on the western 
coast. 
Some vague objections have been stated to the identity 
of the Niger and Zaire, from their difference of tempera- 
ture, the precise meaning of which it is not easy to com- 
