RESTORATION OF THE WATER. 465 
The new canals executed and projected will greatly increase 
the loss. The water required for irrigation in Egypt is less 
than would be supposed from the exceeding rapidity of evapo- 
ration in that arid climate; for the soil is thoroughly saturated 
during the inundation, and infiltration from the Nile continues 
to supply a considerable amount of humidity in the dryest sea- 
son. Linant Bey computed that, in the Delta, fifteen and one- 
third cubic yards per day sufficed to irrigate an acre. If we sup- 
pose water to be applied for one hundred and fifty days during 
the season of growth, this would be equivalent to a total precipi- 
tation of about seventeen inches and one-third. Taking the area 
of actually cultivated soil in Egypt at the estimate of 4,500,000 
acres, and the average amount of water daily applied in both 
Upper and Lower Egypt at twelve hundredths of an inch in 
depth, we have an abstraction of about 74,000,000 cubic yards, 
which—the mean daily delivery of the Nile being in round 
numbers 820,000,000 cubic yards—is twenty-three per cent. of 
the average quantity of water contributed to the Mediterranean 
by that river.* 
In estimating the effect of this abstraction of water upon the 
volume of great rivers, especially in temperate climates and in 
countries with a hilly surface, we must remember that all the 
water thus withdrawn—except that which is absorbed by vegeta- 
tion, that which enters into new inorganic compounds, and that 
which is carried off by evaporation—is finally restored to the 
original current by superficial flow or by infiltration. It is 
generally estimated that from one-third to one-half of the water 
applied to the fields is absorbed by the earth, and this, with the 
deductions just given, is returned to the river by direct infiltra- 
tion, or descends through invisible channels to moisten lower 
* The proportion of the waters of the Nile withdrawn for irrigation is great- 
er than this calculation makes it. The quantity required for an acre is less 
in the Delta than in Upper Ezypt, both because the soil of the Delta, to 
which Linant Bey’s estimate applies, lies little higher than the surface of the 
river, and is partly saturated by infiltration, and because near the sea, in N. L. 
30°, evaporation is much less rapid than it is several degrees southwards and 
in the vicinity of a parched desert. 
