more. Five great
caravan roads cross the Sahara from north to south.

Let us set out on a journey from Timbuktu, and let us go first eastwards
to the singular Lake Chad, which is half filled with islands, is shallow
and swampy, choked with reeds, rises and falls with the discharge of the
great rivers which flow into it, and has a certain similarity to Lop-nor
in Central Asia. Nearly 17 cubic miles of water are estimated to enter
Lake Chad in the year, and when we know that the lake on the whole
remains much about the same size, we can conceive how great the
evaporation must be.

We have our own dromedaries and our own Arab guide on whom we can rely.
We can therefore go where we like, and we steer our course from Lake
Chad towards the eastern Sudan, where we have already been in the
company of General Gordon. But before we come to the Nile we turn off
northwards to cross the Libyan desert, the most inaccessible and
desolate, and therefore the least known, part of the Sahara. On our way
northwards we notice that animal and vegetation life becomes more
scanty. Even in the Sudan the grasslands are more thinly clothed and
the steppes more desert-like the farther we travel, and at last blown
sand predominates. We must follow a well-known road which has been used
for thousands of years by Arabs and Egyptians.

[Illustration: PLATE XXXI.

A GROUP OF BEDUINS.]

We are in the midst of the sea of sand. Here lie at certain places dunes
of reddish-yellow drift sand as high as the tower of St. Paul's
Cathedral. We see no path, for it has been swept away by the last storm;
but the guide has his landmarks and does not lose his way. The sand
becomes lower and the country more open. Then the guide points to a bare
and barren ridge which rises out of the sand like a rock out of the sea,
and says that he can find his way by this landmark, which remains in
sight for several days, and is then replaced by another elevation.

We encamp at a deep well, drink and water our camels. Next day we are
out in the sandy sea again. The sky has assumed an unusual hue. It is
yellow, and soon changes into bluish grey. The sun is a red disc. It is
calm and sultry. The guide looks serious, and says in a low tone
"samum." The hot, devastating desert storm which is the scourge of
Arabia and Egypt is approaching.

The guide stops and turns round. He is uncertain. But he goes on again
when he sees that we cannot get back to the well before the storm is