546 COSMOS. 



to the calculation of its elements, across t7ie Sun's disc on the 

 26th of June ; l * unfortunately its passage was not observed. 

 This must also have been the case with the Comet of 1823, 

 which, besides the ordinary tail turned from the Sun, had 

 also another turned directly towards it. If the tails of both 

 comets had a considerable length, vaporous parts of them must 

 have mixed with our atmosphere, as certainly often happens. 

 The question has been raised as to whether the wonderful 

 mists of 1783 and 1831, which covered a great part of the Con- 

 tinentj were consequences of such an admixture? 11 



While the quantity of radient heat received by the Comets 

 of 1680 and 1843 in such close proximity to the Sun has 

 been compared to the focal temperature of a 32-inch burning 

 mirror;" a highly-deserving 1 ' astronomical friend of mine 



14 Galle, in the Supplement to Gibers' CometenbaJmen, 

 p. 221, no. 130. (With respect to the probable passage of 

 the two-tailed comet of 1823, see Edinb. Eev. 1848, no. 175, 

 p. 193.) The treatise shortly before quoted in the text, con- 

 taining the true elements of the Comet of 1680, contradicts 

 Halley's fantastic idea, according to which, with a presumed 

 period of 575 years, it had appeared at all the great epochs 

 of the human race : at the time of the Deluge according to 

 Hebrew traditions, in the age of Ogyges according to Greek 

 traditions, at the Trojan war, on the destruction of Nineveh, 

 on the death of Julius Caesar, &c. The period of revolution 

 resulting from Encke's calculation is 8814 years. The least 

 distance from the surface of the Sun was, on the 17th of 

 December, 1680, only 128,000 geographical miles; conse- 

 quently 80,000 less than the distance of the Earth from the 

 Moon. The aphelion is 853-3 times the distance of the Earth 

 from the Sun, and the proportion of the smallest to the greatest 

 distance from the Sun is as 1 : 140000. 



lf Arago, in the Annuaire pour 1832, pp. 236-255. 



18 Sir John Herschel, Outlines, . 592. 



" Bernhard von Lindenau, in Schumacher, Astr. Nadir. 

 no. 698, p. 25. 



