Page:The Scientific Monthly vol. 3.djvu/541

 WHAT WE KNOW ABOUT COMETS S35

In some comets only one of these three classes of tails is present, and again in one and the same comet all of the classes may be present at the same time.

That there is outward motion of the tail materials admits of no doubt. It is not uncommon for the tail materials of one night to be driven off into space, scattered and lost to sight, and for an entirely

��Fia. 0. Comet Bhooks on Octobeb 21 akd Octobeh 22, 1803.

new tail to take its place by the following night. A comet's tail is constantly forming and moving out. The tails of comet Kordame (Fig. 8) photographed by Hussey on two successive nights, July 12 and 13, 1893, have no points of resemblance. The streamers composing the tail on one night are fairly straight, regular, and rather faint. The

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