erefore, that the chances of the voyagers, whose ultimate
safety depended so largely upon the staying power of their aerial
vessel, might have been considerably increased.

One other expedient, wholly impracticable, but often seriously
discussed, may be briefly referred to, namely, the idea of taking up
apparatus for pumping gas into metal receivers as the voyage proceeds,
in order to raise or lower a balloon, and in this way to prolong its
life. Mr. Wenham has investigated the point with his usual painstaking
care, and reduced its absurdity to a simple calculation, which should
serve to banish for good such a mere extravagant theory.

Suppose, he says, the gas were compressed to one-twentieth part of its
bulk, which would mean a pressure within its receiver of 300 lbs. per
square inch, and that each receiver had a capacity of 1 cubic foot,
while for safety sake it was made of steel plates one-twentieth of an
inch thick, then each receiver would weigh 10 lbs., and to liberate
1,000 feet clearly a weight of 500 lbs. would have to be taken up. Now,
when it is considered that 1,000 cubic feet of hydrogen will only
lift 72 lbs., the scheme begins to look hope less enough. But when the
question of the pumping apparatus, to be worked by hand, is contemplated
the difficulties introduced become yet more insuperable. The only
feasible suggestion with respect the use of compressed gas is that of
taking on board charged cylinders under high pressure, which, after
being discharged to supply the leakage of the balloon could, in an
uninhabited country, be cast out as ballast last. It will need no
pointing out, however, that such an idea would be practically as futile
as another which has gravely been recommended, namely, that of heating
the gas of the balloon by a Davy lamp, so as to increase its buoyancy
at will. Major Baden-Powell has aptly described this as resembling "an
attempt to warm a large hall with a small spirit lamp."

In any future attempt to reach the Pole by balloon it is not
unreasonable to suppose that wireless telegraphy will be put in
practice to maintain communication with the base. The writer's personal
experience of the possibilities afforded by this mode of communication,
yet in its infancy, will be given.

CHAPTER XXV. THE MODERN AIRSHIP--IN SEARCH OF THE LEONIDS.

In the autumn of 1898 the aeronautical world was interested to hear
that a young Brazilian, M. Santos Dumont, had completed a somewhat no