viii PREFACE.
It would at first sight appear that, the discovery of
the lake sources of the Nile had completely solved the
mystery of ages, and that the fertility of Egypt depended
upon the rainfall of the equator concentrated
in the lakes Victoria and Albert; but the exploration
of the Nile tributaries of Abyssinia divides the Nile
system into two proportions, and unravels the entire
mystery of the river, by assigning to each its due share
in ministering to the prosperity of Egypt.
The lake-sources of Central Africa support the life
of Egypt, by supplying a stream, throughout all
seasons, that has sufficient volume to support the
exhaustion of evaporation and absorption ; but this
stream, if unaided, could never overflow its banks, and
Egypt, thus deprived of the annual inundation, would
simply exist, and cultivation would be confined to the
close vicinity of the river.
The inundation, which by its annual deposit of mud
has actually created the Delta of Lower Egypt, upon
the overflow of which the fertility of Egypt depends,
has an origin entirely separate from the lake-sources of
Central Africa, and the supply of water is derived
exclusively from Abyssinia.
PREFACE. ix
The two grand affluents of Abyssinia are, the Blue
Nile and the Atbara, which join the main stream
respectively in N. lat. 15° 30' and 17° 37'. These rivers,
although streams of extreme grandeur during the
period of the Abyssinian rains, from the middle of
June until September, are reduced during the dry
months to utter insignificance; the Blue Nile becoming
so shallow as to be unnavigable, and the
Atbara perfectly dry. At that time, the water supply
of Abyssinia having ceased, Egypt depends solely upon
the equatorial lakes, and the affluents of the White
Nile, until the rainy season shall again have flooded
the two great Abyssinian arteries. That flood occurs
suddenly about the 20th June, and the grand rush of
water pouring down the Blue Nile and the Atbara
into the parent channel, inundates Lower Egypt,
and is the cause of its extreme fertility.
Not only is the inundation the effect of the Abyssinian
rains, but the deposit of mud that has formed
the Delta, and which is annually precipitated by the
rising waters, is also due to the Abyssinian streams,
more especially to the river Atbara, which, known as
the Bahr el Aswat (Black River) carries a larger pro