116 
MR. HORNER ON THE ALLUVIAL LAND OF EGYPT. 
Egyptian cubits, informs us, that every cubit is divisible into fourteen parts, each of 
two digits, and the length of the cubit being 20‘625 inches, we have 0'736 inch for 
each digit. It will thus be seen that the measurements of Sir G. Wilkinson and 
those of the French engineers very nearly agree, the difference being only between 
2075 and 20-625. 
Upon the island of Rhoda near Cairo a Nilometer was erected more than a 
thousand years ago, and is the only measure of the rise and fall of the Nile referred 
to in the present day. It is known by the name of the Mekyas (instrument of mea- 
sure). For a reason that will afterwards appear, I give the description of it by the 
French engineers in 1800. They describe it as an octagonal pillar, having a scale 
divided into 16 cubits, and each cubit into 24 digits. Each cubit of this scale they 
found to be equal to 541 millimetres, or 21-3 English inches*. 
Between the first entrance of the Nile into Egypt and its mouth, the mass of water 
must be vastly diminished from the following causes: it receives no tributary; 
spread over so wide a surface under a burning sun and a cloudless sky, the evapora- 
tion must be very great; the water is drawn off from the main 'channel by number- 
less canals, and there is a further absorption by infiltration through the soil, for 
several miles inland, on the left bank in Upper Egypt, and on both sides in Lower 
Egypt. Thus, while the rise of the river at the island of Rhoda on an average 
of years is 24 feet, near Ramanyeli about sixty-five miles in a direct line north of the 
apex of the Delta, the difference between highest and lowest water is about 13 feet, 
and at Rosetta and Damietta not more than 42 inches 7 . 
From observations made in 1799 at Siut, about midway between Assouan and 
Cairo, the French engineers estimated the volume of water in the Nile to be as fol- 
lows : — that every second of time a mass of water passes a given line across the river 
equal to 678 cubic metres at low Nile, and 10,247 cubic metres at high Nile^. 
Linant Bey states that the volumes near Cairo are 414 cubic metres at low Nile, and 
9440 at high Nile. M. Talabot makes on this subject the following observations : — 
“En partant des donnees qui fournit M. Girard dans son Memoire sur la Vallee 
d’Egypte, j’ai cherche a calculer le produit moyen du Nil ; il resulte de ce calcul, que 
la hauteur moyenne du Nil, d’apr^s les quatre annees d’observations certaines qui 
nous ont ete fournies, soit par I’Expedition, soit par M. Mougel, etant de 3“’-23, 
correspondrait a un debit moyen de 2860 metres cubes par seconde, ou d’environ 
90,000 millions de metres cubes par an.” But the Rosetta branch, at its mouth, is 
not more than about 600 metres (656 yards) wide, and at lowest water the depth is 
only T60 metre (5 feet 3 inches); in the Damietta branch the width is about 300 
metres (328 yards), and the depth, at the same period, 2-50 metres (8 feet 2| 
inches)^. 
* Description de I’Egypte, vol. xviii. p. 603. 
t Lancret et Chabrol, Descr. de I’Egypte, Etat Moderne, tome ii. p. 187. 
+ Girard, loc. cit. 208. § Girard. 
