We now approach one of Wise's boldest, and at the same time most valuable, experiments. It was the summer of 1839, and once again the old trouble of spontaneous combustion had destroyed a silk balloon which was to have ascended at Easton, Pa. Undeterred, however, Wise resolutely advertised a fresh attempt, and, with only a clear month before the engagement, determined on hastily rigging up a cambric muslin balloon, soaking it in linseed oil and essaying the best exhibition that this improvised experiment could afford. It was intended to become a memorable one, inasmuch as, should he meet with no hindrance, his determination was nothing less than that of bursting this balloon at a great height, having firmly convinced himself that the machine in these circumstances would form itself into a natural parachute, and bring him to earth with every chance in favour of safety. In his own words, "Scientific calculations were on his side with a certainty as great and principles as comprehensive as that a pocket-handkerchief will not fall as rapidly to the ground when thrown out of a third storey window as will a brick." His balloon was specially contrived for the experiment in hand, having cords sewn to the upper parts of its seams, and then led down through the neck, where they were secured within reach, their office being that of rending the whole head of the balloon should this be desired. On this occasion a cat and a dog were taken up, one of these being let fall from a height of 2,000 feet in a Cocking's parachute, and landing in safety, the other being similarly dismissed at an altitude of 4,000 feet in an oiled silk balloon made in the form of a collapsed balloon, which, after falling a little distance, expanded sufficiently to allow of its descending with a safe though somewhat vibratory motion. Its behaviour, at any rate, fully determined Wise on carrying out his own experiment.