COMETS INCLUDED WITHIN SATURN'S ORBIT, 



century, the epoch signalised by the discoveries and researches of 

 Newton. In most cases, however, the only circumstance recorded 

 was the appearance of the object, accompanied in many instances 

 with details bearing evident marks of exaggeration respecting its 

 magnitude, form, and splendour. In some few cases, the con- 

 stellations through which the object passed successively, with the 

 necessary dates, are mentioned, and in some, fewer still, obser- 

 vations of a rough kind have been handed down. From such 

 scanty data, eagerly sought for in the works preserved in different 

 countries, sufficient materials have been collected for the com- 

 putation, with more or less approximation, of the elements of the 

 orbits of about sixty of the 400 comets above mentioned. 



Since the time of Newton, Halley, and their contemporaries, 

 observers have been more active, and have had the command of 

 instruments of considerable and constantly increasing power ; so 

 that every comet which has been visible from the northern hemi- 

 sphere of the earth since that time, has been observed with 

 continually increasing precision, and data have been in all cases 

 obtained, by which the elements of the orbits have been calculated. 

 Since the year 1700, accordingly, about 140 have been observed, 

 the elements of the orbits of which have been ascertained with 

 great precision. 



It appears, therefore, that of the entire number of comets which 

 have appeared in the firmament, the orbits of about 200 have 

 been ascertained. Of this number forty have been ascertained, 

 some conclusively, others with more or less probability, to revolve 

 in elliptic orbits. 



Seven have passed through the system in hyperbolas, and con- 

 sequently will not visit it again, unless they be thrown into other 

 orbits by some disturbing force. 



One hundred and sixty have passed through the system either 

 in parabolic orbits, or in ellipses of such extreme eccentricity as 

 to be undistinguishable from parabolas by any data supplied by 

 the observations. 



II. ELLIPTIC COMETS REVOLVING WITHIN THE ORBIT OF 

 SATURN. 



19. In 1818, a comet was observed at Marseilles, on the 26th 

 of November, by M. Pons. In the following January, its path 

 being calculated, M. Arago immediately recognised it as identical 

 with one which had appeared in 1805. Subsequently, M. Encke 

 of Berlin succeeded in calculating its entire orbit inferring the 

 invisible from the visible part and found that its period was 



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