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X. to the fact that 18 persons had seen the comet at Lausanne and several at Berne, but that bad weather had prevented any observations at Geneva or Paris, he says:—"Astronomers must judge for themselves whether the phenomenon described was that of a celestial body; and if it could have been possible that any merely atmospheric phenomenon could have maintained steadily during 24 hours its condition unchanged, its size and colour the same, its position with respect to the fixed stars the same, and have participated with them in the diurnal movement." De Chéseaux reckons his 24 hours from the night of March 7-8 to the following night of March 8-9, after which he never saw the comet again. He adds that "the sky was very serene without the least cloud or haze, and that both Sun and Moon, (to one or other of which only could the phenomenon be ascribed if it was only atmospheric,) were both of them too far away from the point of convergence of the tails." He then offers some further remarks directed to show that if the rays were tails of a comet, which had its head below the horizon, everything would be explained satisfactorily.

The Comet of 1811 (i.) is one of the most celebrated of modern times. It was discovered by Flaugergues at Viviers on March 26, 1811, and was last seen by Wisniewski at Neu-Tscherkask in the south of Russia on Aug. 17, 1812, a visibility of 17 months—a period then unprecedented. It was a result of this long visibility that, owing to the Earth's annual motion, the comet twice disappeared in the Sun's rays, and twice reappeared after having been in conjunction with the Sun. In the autumnal months of 1811 it shone very conspicuously with a bright nucleus and tail, which became visible soon after sunset and continued visible throughout the night for many weeks, owing to its high northern declination. The extreme length of the tail is dated for the 1st week in October, and was about 25°, with a breadth of about 6°.