. Elements of astronomy: accompanied with numerous illustrations, a colored representation of the solar, stellar, and nebular spectra, and celestial charts of the northern and the southern hemisphere. naked eye. A violent action soon commences ; the gas bursts forthin jets from the coma toward the Sun, and is instantlydriven back again, as the steam of a locomotive going atgreat speed is driven back on its path, though from a dif-ferent cause. The jets rapidly change their position anddirection, and a tail is formed, which seems to consist ofthe smoke or products of combustion driven off from
. Elements of astronomy: accompanied with numerous illustrations, a colored representation of the solar, stellar, and nebular spectra, and celestial charts of the northern and the southern hemisphere. naked eye. A violent action soon commences ; the gas bursts forthin jets from the coma toward the Sun, and is instantlydriven back again, as the steam of a locomotive going atgreat speed is driven back on its path, though from a dif-ferent cause. The jets rapidly change their position anddirection, and a tail is formed, which seems to consist ofthe smoke or products of combustion driven off from thecoma, probably by the repulsive power of the Sun, andrendered visible by his light. The tail is always turnedaway from the Sun, whether the comet be approaching orreceding from that body. As the comet gets still nearer to the Sun, and there-fore to the Earth, we begin to see in some instances thatthe coma contains a nucleus, brighter than itself; the jets there that both head, and tail are transparent ? Mention a case in point. changes of appearance take place, as a comet approaches the Sun? Inwhat direction is the tail always turned ? What does the coma sometimes con- 160 are distinctly visible, and some-times the coma consists of aseries of envelopes. This wasthe case in the beautiful cometof 1858; the nucleus was con-tinually throwing off these en-velopes, which surrounded itlike the layers of an onion, andpeeled off, expanding outwardand giving place to distinct envelopes werethus seen; as they were drivenoff, they seemed to be expelledinto the tail. Hence the tails of comets,as a rule, rapidly increase asthey approach the Sun, whichgives rise to all this violent ac-tion. The tail of the comet of 1861 was 20,000,000 mileslong, and this length has been exceeded in many cases. Thetail of the comet of 1843 was 112,000,000 miles long, thediameter of the coma being 112,000 miles, that of the nu-cleus 400 miles; near perihelion, the tail increase
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectastronomy, bookyear18
