I shall now give the length of the Nile along its course from Abu Hammed to the island of Philæ, at the head of the cataract of Assuan. I employ for this purpose the map in the atlas which accompanies the work of Russegger, which bears the date of 1846, and which, doubtless, was constructed on the best authorities. He mentions a map of General von Prokesch with great praise.[58] It flows:—

German M.English M.
From NE. to SW., from Abu Hammed to Meroë, about31=150
It makes a curve between Meroë and Old Dongola, of about16=77
It flows between Old and New Dongola, from SE. to NW., about16=77
Then, with some short windings, nearly due north to the island of Sais, for about30=145
And from Sais to the island of Philæ, from SW. to NE., about68=327
Making the whole length of the course, from Abu Hammed to Philæ, about161=776

Ascending the river, we have, between Philæ and Korusko, a distance of 24 German, or 115½ English miles, and without any rapid, except one near Kalabsche. Korusko being 115 feet above the head of the cataract of Assuan, at Philæ, we have an average fall of the river between these two places of a foot in a mile.

Between Korusko and Wadi-Halfa there is no rapid. The distance being 20 German, or 96⅓ English miles, and the difference of altitude being 42½ feet, we have an average fall throughout that part of the river's course of not more than 5·3 inches in a mile.

This very inconsiderable fall need not surprise us; for the average fall of the Nile in Lower Egypt, at the lowest water, is little more than one-third of that now stated. At the time of the highest water the surface of the Nile, at Boulak, near Cairo; that is, about 116 miles in a direct line from the coast is only 43·437 English feet above the level of the Mediterranean, and at the time of the lowest water, only 17·33 feet. Thus, in the first case, there is an average fall of about 5·00 inches; in the second, of not more than 1·80 inches in a mile.[59]

Between Wadi Halfa and Dale, a distance of about 94 miles, six cataracts, or schellals, as they are called in the language of the country, are marked in Russegger's map. And here, it may be as well to notice, that there are no cataracts, in the ordinary sense of the term, on the Nile; no fall of the river over a precipice; all the so-called cataracts are rapids, where the river rushes through rocks in its bed; the rapids varying in their length and degrees of inclination. We have no measurements of their lengths or of their falls, except as regards the first and second cataracts. The former, according to Russegger, has a fall of about 85 English feet in a distance of about 8 miles; and he describes the latter as extending from 5 to 6 stunden; that is, from 12 to 14½ miles, but he does not give the height. Speaking of the schellals above Semne, Russegger says, that all may be passed in boats without difficulty for about six weeks, or two months in the year. This is the case also, at the cataract or rapid of Assuan. But between Wadi-Halfa and Dale, with some inconsiderable spaces of free navigable water, in the ordinary state of the river, there is an almost uninterrupted series of rapids. We have no measurement of the height of Dale above Wadi-Halfa, near to which the second great cataract of the Nile occurs; but this is the part of the river's course where the fall is greatest, and from Semne to Dale there are about 45 miles of this more rapid fall.

From Dale to New Dongola, a distance of 35 German, or about 168 English miles, only three rapids are marked on Russegger's map—the highest being at Hannek, about 26 English miles below New Dongola. New Dongola being 806 English feet above the sea, and the distance from that place to the rapid of Hannek being 26 miles only, we may with probability estimate the surface of the river at the rapid of Hannek at 780 feet above the sea. Now, Wadi-Halfa being 522 feet, we have a difference of height, between these two last-named places, of 258 feet; and the length of the river's course between them being 236 miles, we have an average fall of 13·12 inches in a mile; that is, in the part of the river's course where nine rapids occur, in the provinces of Batn-el-Hadjar, Sukkot, and Dar-el-Mahass, where the river flows over granite and other plutonic rocks; gneiss, mica-schist, and other hard rocks, which Russegger considers to be metamorphic. But between Semne and the head of the second cataract at Wadi-Halfa, there is not a continuous rapid stream; for Hoskins says, that about two miles above that cataract, the river has a width of a third of a mile, and, when he passed it the water was scarcely ruffled.[60]

From the rapid of Hannek to Abu Hammed, the distance is 329 English miles, and the difference of altitude is 246 English feet. We have thus an average fall in that distance of 9·00 inches in a mile.

Thus, in the 776 miles between Abu Hammed and Philæ, we have an average fall of the Nile

Of 9·00inches in a mile,for a distance of329miles.
Of 13·12..................236...
Of 5·30..................96...
Of 12·00..................115...