ty of the Nigir, in which an
approximation is all that can be expected or required. Having been
totally ignorant of the countries through which that river flows in a
southerly direction, Ptolemy naturally mistook it for a river of the
interior; he knew the middle Ethiopia to be a country watered by
lakes, formed by streams rising in mountains to the southward; he was
superior to the vulgar error of supposing that all the waters to the
westward of the Nile flowed into that river, and he knew consequently
that the rivers and lakes in the middle region, had no communication
with the sea. It is but lately that we ourselves have arrived at a
certainty on this important fact. We now know enough of the level of
the Lake Tchad, to be assured that no water from that recipient can
possibly reach the Nile. This wonderful river, of which the lowest
branch is 1200 geographical miles from the Mediterranean, (measuring
the distance along its course, in broken lines of 100 G.M. direct,)
has no tributary from the westward below the Bahr Adda of Browne,
which is more than 1600 miles from the sea, similarly measured. It is
scarcely possible, therefore, that the latter point can be less,
taking the cataracts into consideration than 1500 feet above the sea,
whereas the following considerations lead to the belief that the
Tchadda is not more than 500 feet in height.

We learn from the information of Clapperton, confirmed and amplified
by that of Lander, that there exists a ridge, which about Kano and
Kashna, extends forth the Yeu to the Lake Tchadda on one side, and on
the other the river of Soccatoo, which joins the Quorra at a distance
from the sea of about 500 miles, measured in the manner above
mentioned. A similar process of measurement gives a length of 1700
miles to the whole course of the Quorra, the sources of which,
according to Major Laing, are about 1600 feet above the sea; the
stream, therefore, has an average fall of something less than a foot
in a mile in lines of 100 geographical miles. This would give to the
confluence of the river of Soccatoo with the Quorra, a height of less
than 500 feet above the sea, but as that confluence occurs above the
most rapid part of the main stream, 500 feet seem to be very nearly
the height.

As a knowledge of the origin and course of rivers, conducts in every
country to that of the relative altitude and directions of its
highlands, the late discoveries on the waters of Africa have thrown
g