Elements of astronomy ..with explanatory notes, and questions for examination . ey are lost from view in his bril-liant rays. Upon emerging into sight on the other sideof the sun, the comet attains its greatest brightness, andthe tail, now extended to its utmost limit, shines forthin full splendor. As the comet departs from the sun,the tail gradually loses its radiance, and decreases inlength till it is absorbed in the head. 633. In Fig. 78, where the comet of 1819, is delin-eated, its three distinct parts are easily recognized. 634. Number of Comets. This class of celestialbodies is without d
Elements of astronomy ..with explanatory notes, and questions for examination . ey are lost from view in his bril-liant rays. Upon emerging into sight on the other sideof the sun, the comet attains its greatest brightness, andthe tail, now extended to its utmost limit, shines forthin full splendor. As the comet departs from the sun,the tail gradually loses its radiance, and decreases inlength till it is absorbed in the head. 633. In Fig. 78, where the comet of 1819, is delin-eated, its three distinct parts are easily recognized. 634. Number of Comets. This class of celestialbodies is without doubt very numerous, for, according toSir John Herschel, the list of those on record before theinvention of the telescope amounts to several hundred. 1. Comet from the Greek kome, signifying hair. Describe each of them in full 1 Do all comets possess tails or trains 1 Does a cometever have more than one ? State the changes to which these appendages are subject 1What is said respecting the number of comets on record before tbe telescope was invented 1 264 SOLAR SYSTEM. FIG COMET OF 1819. The telescope has added materially to this number, fornot a year passes without some being brought to lightfrom the depths of that obscurity in which they musthave forever remained, if the astronomer had continuedto gaze upon the heavens with his unaided eye. Withinthe last century, more than 140 comets have been seenwhich have not yet made their second appearance. 635. Thirty comets are known to have their periheliondistances within the orbit of Mercury, and M. Arago basinghis calculations upon this fact, and also upon the suppo-sition that comets are uniformly distributed throughspace, has computed that 8,529,470 comets have theirperihelion distances within the orbit of Uranus. Moreoversince comets may come within the limits of our solarsystem and yet be invisible to us, even with the telescopein consequence of daylight, the prevalence of fogs andclouds, and also from their being within th
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