of Denham and Clapperton, to justify the application of the name Nigir to the whole course of the river.  Although we find Ptolemy to be misinformed on several points concerning central Africa, yet there still remains enough in his Data, on Interior Libya and Northern Ethiopia, to show a real geographical approximation, very distant indeed from the accuracy at which science is always aiming, but quite sufficient to resolve the question as to the identity 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.