At twenty minutes before nine o'clock, the mercury attained its limit, or ran down, in the barometer. The instrument then indicated an altitude of twenty-five miles, and I consequently surveyed at that time an extent of the earth's area amounting to no less than one three-hundred-and-twentieth part of the entire surface. At half-past nine, I tried the experiment of throwing out a handful of feathers through the valve. They did not float as I had expected, but dropped down like a bullet and with the greatest velocity, being out of sight in a very few seconds. It occurred to me that the atmosphere was now far too rare to sustain even feathers; that they actually fell, as they appeared to do, with great speed, and that I had been surprised by the united velocities of their descent and my own rise. At six o'clock P. M., I perceived a great portion of the earth's visible area to the eastward involved in thick shadow, which continued to advance with great rapidity, until at five minutes before seven the whole surface in sight was enveloped in the darkness of night. It was not, however, until long after this time that the rays of the setting sun ceased to illumine the balloon, and this fact, although, of course, expected, did not fail to give me great pleasure. In the morning I should behold the rising [v]luminary many hours before the citizens of Rotterdam, in spite of their situation so much farther to the eastward, and thus, day after day, in proportion to the height ascended, I should enjoy the light of the sun for a longer and longer period. I now resolved to keep a journal of my passage, reckoning the days by twenty-four hours instead of by day and night. At ten o'clock, feeling sleepy, I determined to lie down for the rest of the night; but here a difficulty presented itself, which, obvious as it may appear, had escaped my attention up to the very moment of which I am now speaking. If I went to sleep, as I proposed, how could the air in the chamber be renewed in the meanwhile? To breath it more than an hour at the farthest would be impossible; or, even if this term could be extended to an hour and a quarter, the most ruinous consequences might ensue. This dilemma gave me no little anxiety; and it will hardly be believed that, after the dangers I had undergone, I should look upon this business in so serious a light as to give up all hope of accomplishing my ultimate design, and finally make up my mind to the necessity of a descent. But this hesitation was only momentary. I reflected that man is the slave of custom and that many things are deemed essential which are only the results of habit. It was certain that I could not do without sleep; but I might easily bring myself to feel no inconvenience from being awakened at intervals of an hour during the whole period of my repose. It would require but five minutes to renew the air, and the only difficulty was to contrive a method of arousing myself at the proper moment for so doing.