The vessel had not rounded the Isle of Dogs when we found ourselves in earnest conversation with an elderly gentleman, who was much interested in aërostation. It came out, too, that he had ascended himself, and that he was intimate with some of the aëronautic celebrities of the present century.
“Do you know,” said our communicative fellow-traveller, “I never could thoroughly understand the cause of the fatal descent of that poor man Cocking; being abroad at the time I had not the opportunity of keeping pace with our home newspapers.”
In reply I said, “You are aware that the principle of his parachute was diametrically opposite to Garnerin’s, which had descended successfully. Cocking’s was a sort of inverted cone, while that previously employed was more like an umbrella turned upside down with a weight appended to the stick.”
“Exactly,” said our intelligent acquaintance, “and the tendency of a rush of air was not to collapse but rather to keep it distended.”
I fully agreed, and added that “Two objectionable circumstances attended the use of Garnerin’s parachute, namely, the length of time which elapsed before it expanded, and the violent oscillating movement which accompanied the descent. In order to obviate these deficiencies a variety of plans had been proposed at different times, amongst which was that of Cocking’s.” The inverted cone principle, however, was not an idea originating with Cocking, although he had lectured on the subject in 1814 before the Society of Arts.
“Towards the end of the last century this kind of parachute was proposed in Paris, and revived by Sir George Cayley, and again more fully developed by Mr. Kerr in the Encyclopædia Edinensis.”
“Pray,” inquired our friend, “do you happen to know the weight and diameter of Cocking’s parachute?”
“Yes; the computations which appeared in the public press, previous to the inquest, were loose and incorrect. They were to the effect that the entire weight was 393 lbs., whereas, from the evidence taken before the coroner, it appeared that the apparatus weighed 413 lbs., and Mr. Cocking 170 lbs. The terminal velocity, therefore, would have been nearly twenty feet in a second had the parachute not collapsed. Its diameter was thirty-four feet.”
“Of course one of smaller dimensions on the concave plan would descend less rapidly?”
“Oh, certainly a parachute on the Garnerin principle would bring a man down at the rate of twenty feet in a second, even if it were fifteen feet in diameter.”