84 COSMOS. 



rings which belong to one at least of the outermost planets, 

 as products of tangential force, and as closely connected 

 together by mutual attraction ; it, therefore, now only re- 

 mains for us to speak of the unnumbered host of comets which 

 constitute a portion of the cosmical bodies revolving in inde- 

 pendent orbits round the Sun. If we assume an equable 

 distribution of their orbits, and the limits of their perihelia, 

 or greatest proximities to the Sun, and the possibility of their 

 remaining invisible to the inhabitants of the Earth, and base 

 our estimates on the rules of the calculus of probabilities, we 

 shall obtain as the result an amount of myriads perfectly 

 astonishing. Kepler, with his usual animation of expression,, 

 said, that there were more comets in. the regions of space than 

 fishes in the depths of ocean. As yet, however, there are 

 scarcely one hundred and fifty, \vhose paths have been calcu- 

 lated, if we may assume at six or seven hundred the number 

 of comets, whose appearance and passage through known 

 constellations have been ascertained by more or less precise 

 observations. Whilst the so-called classical nations of the 

 west, the Greeks and Romans, although they may occasionally 

 have indicated the position in which a comet first appeared, 

 never afford any information regarding its apparent path, the 

 copious literature of the Chinese (who observed nature care- 

 fully, and recorded with accuracy what they saw) contains 

 circumstantial notices of the constellations through which each 

 comet was observed to pass. These notices go back to more 

 than five hundred years before the Christian era, and many of 

 them are still found to be of value in astronomical observa- 

 tions.* 



* The first comets of whose orbits we have any knowledge, and which 

 were calculated from Chinese ob,ervations, are those of 240 (under 

 Gordian III.), 539 (under Justinian), 565, 568, 574, 837, 1337, and 

 1385. See John Eussell Hind in Schum. Astr. Nadir., 1843. No. 498. 

 Whilst the comet of 837 (which, according to du Sejour, continued during 

 24 hours within a distance of 2,000,000 miles from the Earth) terrified 

 Lou'S I. of France to that degree, that he busied himself in building 

 churches and founding monastic establishments, in the hope of ap- 

 peasing the evils thrcatent-d by its appearance, the Chinese astrono- 

 mers made observations on the path of this cosmical body, whose tail 

 extended over a space of 60, appearing sometimes single and some- 

 times multiple. The first comet that has been calculated solely from 

 Europ an observations was that of 1456, known as Halley's comet, from 

 the belief long, but erroneously entertained, that the period when 



