Comets calculated before 1849, retrograde,
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100
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Great comet of 1861, distance from the Earth on June 30, .
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17,000,000
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Great comet of 1861,— — — surmised by Hind that the Earth passed through its tail,
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30th June
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Great comet of 1861,— — — length of tail as seen at Rome
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118°
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Great comet of 1861, length of tail— — — as seen at Paris
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45°
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Great comet of 1861,— — — polarisation of tail strong, but no trace in nucleus till
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3d July
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Great comet of 1861,— — — tail seen to flicker and disappear for an instant.
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4th July
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Encke's comet, before perihelion, diameter diminished in two months to
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1-90th
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Encke's comet— — — after perihelion, diameter increased in six days from 1 to .
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40
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Rotation of comet of 1825 (doubtful),
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19h. 37m.
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Mass of Lexell's comet less than (Earth's = 1)
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1-5000th
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Chances unfavourable to collision between earth and a comet (comet's diam. = l-4th of earth's),
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281,000,000
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