f them back in a huge reservoir, until the
rain-regions, from which they came, began to stop supplies, and the
river sank to its usual size. Then the gates of the reservoir could be
opened, and the pent-up flood be allowed to gush forth again to refresh
the thirsty fields.

In 1898 the performance of this task was undertaken by the engineering
firm of John Aird & Co.,[1] at a cost of two million pounds, and in May
of that year the scene of operations was chosen, four miles south of the
town of Assuan. Here it was proposed to erect a dam, or barrier, right
across the Nile. It would stand on the crest of a cataract and would be
one mile and a quarter long. But as the river at flood-time carries down
large quantities of rich deposit which is extremely beneficial to the
soil on which it settles, it would never do to erect any obstruction to
check this in its flow. Therefore this Nile dam must be a barrier
capable of letting the river pass until its treasure was safely
delivered in Egypt. _Then_ the waters must be checked and the great
reservoir filled. This could only be done by means of a number of
sliding doors in the dam, which could be opened and closed at will.

[Footnote 1: To whom we are indebted for permission to reproduce the
illustrations of the Dam.]

The first examination of the cataract seemed to show that it flowed over
sound, hard rock, and no difficulty was expected in finding a good, firm
foundation. But when, to keep the water back while the work was in
progress, sand-banks and temporary dams were built across the four
channels through which the river flows to the cataract in the spring, it
was found that the granite of the river-bed was 'rotten,' and in many
places it was necessary to dig down thirty feet, before solid rock could
be found. This was a sad surprise, for it seemed impossible to start
building at such a depth, and carry the masonry to a sufficient height
before the Nile in flood would come roaring down to Assuan. It was a
race with time; and if the engineers failed to win, their temporary dams
would be washed away, and would have to be built again next year before
the great barrier could be gone on with. Already the Nile had more than
once laughed at these temporary banks of sand and stone, and had broken
through them and leapt upon its course as though jeering at human power.
So persistent had been its attacks that the engineers almost despaired
of finding anything heavy enough to hold its