A.Andrews. The Flying Machine: Its Evolution through the Ages (Putnam)

Cayley’s preoccupation with flapper wings (even after he had altered their angle of attack to conform with his discovery of the true way in which a bird propels itself) seems to have derived from a curious mental block. In 1809 a Swiss watchmaker named Jacob Degen was reported from Vienna as having ‘ascended above the trees in the Prater with artificial wings, taken his flight in various directions, and alighted on the ground with as much ease as a bird’. Cayley fully believed this report, that Degen had mastered some moving-wing machine, and his credulity was bolstered when Viscount Mahon sent him a clear sketch of Degen in his wing harness. What the sketch did not show, because two-thirds of it had been cut out, was that Degen was not ‘flying’ at all. He was suspended from a balloon that took over half his weight, and he was performing nothing more than pneumatic bounds, or balloon-hopping. Mahon eventually found this out, actually saw the balloon, and told Cayley; but the baronet seemed to want to believe that Degen had really flown, and 36 years later he was still mentioning this feat as a fact. It gave him throughout his life an altogether unreasonable faith in the functional potential of flappers. Even though he had long discarded any reliance on a moving wing for the support of an aeroplane and had accepted fixed wings, he still tended to incorporate separate flappers for propulsion in preference to airscrews.
   Cayley should have been convinced by the debacle in 1811 of Albrecht Berblinger, the famous ‘Tailor of Ulm’, who tried to take off with Degen’s wings but without his balloon, and crashed straight into the drink in the Danube.
   The melancholy fact that clinched the limitations of Degen’s performance was that, like many another aeronautical experimenter, he was heavily in debt, and had been taken to a debtor’s prison in Vienna. He arranged the balloon-cum-wings demonstration to raise some money. In order that he should not use the balloon to escape from custody, a rope was tied round his body and held by the jailer, so that he could not jump upwards to a height much more than 50ft. When he had finally paid off his debts in Vienna, Degen moved to Paris. He was badly manhandled by a crowd there when his performance was not considered spectacular enough. Paris was always a dangerous place in which to crash back to the drawing board. The crew of a Montgolfiere balloon had endured similar rough treatment there when their display had had to be cancelled because of a technical hitch.