Scientific aerostation has lost its most promising expert by the
untimely death of Walter Powell. He was not a mere sensational
ballooner, nor one of those dreamers who imagine they can invent flying
machines, or steer balloons against the wind by mysterious electrical
devices or by mechanical paddles, fan-wheels, or rudders.
He perfectly understood that a balloon is at the mercy of atmospheric
currents and must drift with them, but nevertheless he regarded it as
a most promising instrument for geographical research. I had a long
conference with him on the subject in August last, when he told me that
the main objects of the ascents he had already made, and should be
making for some little time forward, were the acquisition of practical
skill, and of further knowledge of atmospheric currents; after which
he should make a dash at the Atlantic with the intent of crossing to
America.
On my part, I repeated with further argument what I have already urged
on page 113 of the “Gentleman’s Magazine” for July, 1880, viz., the
primary necessity of systematic experimental investigation of the rate
of exosmosis (oozing out) of the gas from balloons made of different
materials and variously varnished.
Professor Graham demonstrated that this molecular permeation of gases
and liquids through membranes mechanically air-tight, depends upon the
adhesive affinities of particular solids for other particular fluids,
and these affinities vary immensely, their variations depending on
chemical differences rather than upon mechanical impermeability. My
project to attach captive balloons of small size to the roof of the
Polytechnic Institution, holding them by a steelyard that should
indicate the pull due to their ascending power, and the rate of its
decline according to the composition of the membrane, was heartily
approved by Mr. Powell, and, had the Polytechnic survived, would
have been carried out, as it would have served the double purpose of
scientific investigation and of sensational advertisement for the
outside public.
If the aeronaut were quite clear on this point—could calculate
accurately how long his balloon would float—he might venture with
deliberate calculation on journeys that without such knowledge are mere
exploits of blind daring.
The varnishes at present used are all permeable by hydrogen gas and
hydrocarbon coal-gas, as might be expected, _à priori_, from the fact
that they are themselves solid hydrocarbons, soluble in other liquid
or gaseous hydrocarbons. Nothing, as far as I can learn, has yet been
done with _silicic or boracic varnishes_,[22] which are theoretically
impermeable by hydrogen and its carbon compounds; but whether they
are practically so under ballooning conditions, and can be made
sufficiently pliable and continuous, are questions only to be solved by
practical experiments of the kind above named. Now that the best man
for making these experiments is gone, somebody else should undertake
them. Unfortunately, they must of necessity be rather expensive.