PORTION OF THE COSMOS. COMETS. 401 



lution of 87'97 days, with Neptune, whose period is 601 26'7 

 days ; and Encke's comet, having 3*3 years, with the comet 

 of 1680, observed by Gottfried Kirch at Coburg, by Newton 

 and by Halley, whose computed period is 8814 years. I have 

 already noticed (Kosmos, Bd. i. S. 116 118, and Bd. iii. 

 S. 371 373; Engl. edit. Vol.i. p. 102103, and Vol. iii. 

 p. 260 261), the distance of the fixed star nearest to our 

 solar system (a Centauri), from the aphelion (or greatest 

 distance from the Sun) of the last-named comet, as deter- 

 mined by Encke in an excellent memoir on the subject, the 

 very small velocity, 10 feet in a second, of the same comet 

 at the remotest part of its path, and the greatest proximity 

 attained by Lexell's and Burckhardt's comet of 1770 to the 

 Earth, (being 6 distances of the Moon from the Earth), and 

 by the comet of 1680, and still more the comet of 1843, to 

 the Sun. The 2d comet of 1819, which, as seen in Europe, 

 emerged suddenly in considerable magnitude from the Sun's 

 rays, must, according to its elements, have passed on the 

 26th of June ^but, unfortunately, without being seen!) in 

 front of the Sun's disk ( 658 ) . This must also have been the 

 case with the comet of 1823, which, besides the ordinary 

 tail turned from the Sun, had another turned directly towards 

 the Sun. If the tails of these two comets had a considerable 

 length, vaporous particles belonging to them must have 

 become mingled with our atmosphere, as doubtless has 

 often happened. The question has been propounded, whe- 

 ther the extraordinary mists which, in 1783 and 1831, 

 covered a large part of our continent, may have been the 

 result of such an admixture ( 659 ) . 



While the quantity of radiant heat received by the comets 

 of 1680 and 1843, when in such near proximity to the Sun, 



