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nucleus is of extraordinary brightness, shining with the 

 briUiancy of a star of the first magnitude. Not only was the 

 nucleus of the great comet of lc^43 visible in broad daylight, but 

 also a portion of its tail. The comets of 1577, 1680, and 1769 

 were remarkable for the intensity of hie light emitted by the 

 luicleus. Not less uninteresting than the method by which the 

 tail of a comet is formed are those changes in the nucleus which 

 joroduce the envelopes which surround it. This is well illustrated 

 by the beautiful drawings of the comet of 1861, now on the 

 screen. They were made by Mr. Warren de la Rue, on the 2nd 

 and 3rd of July. Under the sun's influence, the nucleus peels or 

 throws off envelopes, as the different layers round an onion peel 

 off, and these are gradually expelled into the tail. These 

 successive phases which the comet of 1858 underwent in this 

 respect are exquisitel}' delineated by the same accomplished 

 astronomer. Now, although, as a general rule, comets, as they 

 approach the sun, become more brilliant, and acquire a luminous 

 train, yet in the case of Encke's and Halley's the tail and coma 

 decreased. We will throw upon the screen, in illustration of this, 

 Halley's comet, as it appeared at an interval of 13 days in 1830. 

 But stiU the question remains, whence come these strange 

 visitors % To what laws are they subject ? Whither are they 

 bound '? Of what substances are they formed ? The gi-eater 

 number of those that have been observed belong undoubtedly to 

 the solar system. They circle in cloud orbits round the centre of 

 our system, thereto constrained by that bond of gravitation 

 which controls the planets. The periods of revolution vary 

 enormously. Encke's comet performs its revolution in 3;^ years, 

 Halley's in 76. The period of the comet of 1680 has been 

 calculated at nearly 9,000 years; that of 18U at 100,000. 

 Some again have never returned, and probably will never revisit 

 our sj'stem. They have escaped from our sun's control, and 

 plunging into the infinite abysses of space, have fallen within the 

 sphere of attractions of other suns than ours. They thus may 

 become wandering messengers as it were, passing from one 



