nflict moving in
rapid gyrations, come in contact with the earth, a singular spectacle
presents itself. Like funnel-shaped clouds, their apexes touching the
earth, the sand rises in vapory form through the rarefied air in the
electrically-charged centre of the whirling current, sweeping on like
the rushing waterspout, which strikes such terror into the heart of the
mariner. A dim and sallow light gleams from the lowering sky over the
dreary plain. The horizon suddenly contracts, and the heart of the
traveller sinks with dismay as the wide steppe seems to close upon him
on all sides. The hot and dusty earth forms a cloudy veil which shrouds
the heavens from view, and increases the stifling oppression of the
atmosphere, while the east wind, when it blows over the long-heated
soil, instead of cooling, adds to the burning glow. Gradually, too, the
pools of water, which had been protected from evaporation by the now
seared foliage of the fan-palm, disappear. As in the icy north animals
become torpid from cold, so here the crocodile and the boa-constrictor
lie wrapt in unbroken sleep, deeply buried in the dried soil. Everywhere
the drought announces death, yet everywhere the thirsty wanderer is
deluded by the phantom of a moving, undulating, watery surface, created
by the deceptive play of the mirage. A narrow stratum separates the
ground from the distant palm-trees, which seem to hover aloft, owing to
the contact of currents of air having different degrees of heat, and
therefore of density. Shrouded in dark clouds of dust, and tortured by
hunger and burning thirst, oxen and horses scour the plain, the one
bellowing dismally, the other with outstretched necks snuffing the wind,
in the endeavor to detect, by the moisture of the air, the vicinity of
some pool of water not yet wholly evaporated.

The mule, more cautious and cunning, adopts another method of
allaying his thirst. There is a globular and articulated plant, the
_Melo-cactus_, which encloses under its prickly integument an aqueous
pulp. After carefully striking away the prickles with its forefeet,
the mule cautiously ventures to apply his lips to imbibe the cooling
thistle juice. But the draught from this living vegetable spring is not
always unattended by danger, and these animals are often observed to
have been lamed by the puncture of the cactus thorn. Even if the burning
heat of day be succeeded by the cool freshness of the night, here always
of equal length, the