After a long and arduous devotion to the study of physics and astronomy, I, Hans Pfaal of Rotterdam, at length determined to construct a balloon of my own along original lines and to try a flight in it. Accordingly, I had made an enormous bag out of cambric muslin, varnished with caoutchouc for protection against the weather. I procured all the instruments needed for a prolonged ascent and finally prepared for the inflation of the balloon. Herein lay my secret, my invention, the thing in which my balloon differed from all the balloons that had gone before. Out of a peculiar metallic substance and a very common acid I was able to manufacture a gas of a density about 37.4 less than that of hydrogen, and thus by far the lightest substance ever known. It would serve to carry the balloon to heights greater than had been attained before, for hydrogen is the gas usually used.

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