must always be remembered that in Andree's case
the rigours of climate which he was compelled to face were the most
serious of all obstacles to balloon travel. The extreme cold would
not only cause constant shrinkage of the gas, but would entail the
deposition of a weight of moisture, if not of snow, upon the surface of
the balloon, which must greatly shorten its life.

It would be entirely otherwise if the country it were sought to explore
were in lower latitudes, in Australia, or within the vast unknown belt
of earth lying nearer the equator. The writer's scheme for exploring the
wholly unknown regions of Arabia is already before the public. The
fact, thought to be established by the most experienced aeronauts of
old times, and already referred to in these pages, that at some height
a strong west wind is to be found blowing with great constancy all
round the globe, is in accordance with the view entertained by modern
meteorologists. Such a wind, too, may be expected to be a fairly fast
wind, the calculation being that, as a general rule, the velocity of
currents increases from the ground at the rate of about three miles
per hour for each thousand feet of height; thus the chance of a balloon
drifting speedily across the breadth of Arabia is a strong one, and,
regarded in this light, the distance to be traversed is certainly
not excessive, being probably well within the lasting power of such a
balloon as that employed by Andree. If, for the sake of gas supply, Aden
were chosen for the starting ground, then 1,200 miles E.N.E. would carry
the voyager to Muscat; 1,100 miles N.E. by E. would land him at Sohar;
while some 800 miles would suffice to take him to the seaboard if his
course lay N.E. It must also be borne in mind that the Arabian sun by
day, and the heat radiated off the desert by night, would be all in
favour of the buoyancy of the balloon.

But there are other persistent winds that, for purposes of exploration,
would prove equally serviceable and sure. From time immemorial the
dweller on the Nile has been led to regard his river in the light of a
benignant deity. If he wished to travel down its course he had but to
entrust his vessel to the stream, and this would carry him. If, again,
he wished to retrace his course, he had but to raise a sail, and the
prevalent wind, conquering the flood, would bear him against the stream.
This constant north wind, following the Nile valley, and thence trending
still southwa