in which the contrasted and hitherto incompatible merits of balloon
and heavy flying machine might be combined in one apparatus,
which should be at choice either heavier or lighter than air.
He took hints from the contractile bladders of fish and the pneumatic
cavities of birds. He devised an arrangement of contractile
and absolutely closed balloons which when expanded could lift
the actual flying apparatus with ease, and when retracted by the
complicated "musculature" he wove about them, were withdrawn
almost completely into the frame; and he built the large framework
which these balloons sustained, of hollow, rigid tubes, the air
in which, by an ingenious contrivance, was automatically pumped
out as the apparatus fell, and which then remained exhausted
so long as the aeronaut desired. There were no wings or propellers
to his machine, such as there had been to all previous aeroplanes,
and the only engine required was the compact and powerful little
appliance needed to contract the balloons. He perceived that such
an apparatus as he had devised might rise with frame exhausted
and balloons expanded to a considerable height, might then contract
its balloons and let the air into its frame, and by an adjustment
of its weights slide down the air in any desired direction. As it fell
it would accumulate velocity and at the same time lose weight,
and the momentum accumulated by its down-rush could be utilised
by means of a shifting of its weights to drive it up in the air again
as the balloons expanded. This conception, which is still the
structural conception of all successful flying machines, needed,
however, a vast amount of toil upon its details before it could
actually be realised, and such toil Filmer--as he was accustomed
to tell the numerous interviewers who crowded upon him in
the heyday of his fame--"ungrudgingly and unsparingly gave."
His particular difficulty was the elastic lining of the contractile