198 cosmos. 



From the summary here given, it follows that, since the 

 discovery of Encke's Cornet^ as an interior one in the year 

 1819, up to the discovery of the interior comet of D' Arrest, 

 scarcely 32 years have elapsed. Yvon Yillarceau has also 

 given elliptic elements for the last-named in Schumacher's 

 Astron. Nachr., No. 773, and has, at the same time with 

 Valz, put forward some conjectures as to its identity with 

 the Comet of 1678, observed by La Hire, and calculated by 

 Douwes. Two other comets, apparently of from 5 to 6 year 

 periods of revolution, are the 3d of 1819, discovered by Pons, 

 and calculated by Encke ; and the 4th of 1819, discovered 

 by Blanpain, and, according to Clausen, identical with the 1st 

 of 1743. But neither of these can be classed with those 

 which, from longer and more accurate observations, present 

 a greater certainty and completeness of their elements. 



The inclination of the orbits of the interior comets to the 

 plane of the ecliptic is, upon the whole, small, between 3° 

 and 13°; that of Brorsen's Comet alone is very considerable, 



* The short period of revolution of 1204 days was discovered by 

 Encke on the reappearance of his comet in the year 1819. See the first 

 calculated elliptical orbits in the Berliner Astron. Jahrbuch for 1822, 

 p. 193, and for the constants of the resisting medium assumed to explain 

 the accelerated revolution. Encke's Vierte Abhandlburg in the Schrif- 

 ten der Berl. Akademie for the year 1844. (Compare Arago, in the^4ra- 

 nnaire for 1832, p. 181 ; in the Lettre a M. Alexandre de Humboldt, 1840, 

 p. 12 ; and Galle, in Olbers's Cometenbahnen, p. 221.) As belonging to 

 the history of Encke's Comet, it must here be called to mind that, so far 

 as our knowledge of the observations extends, it was first seen upon two 

 days by Mechaiu on the 17th of January, 1786; then by Miss Carolina 

 Herschel from the 7th to the 27th of November, 1795; afterward by 

 Bouvard, Pons, and Huth, from the 20th of October to the 19th of No- 

 vember, 1805; finally, as the tenth reappearance since Mechain's dis- 

 covery in the year 1786, by Pons from the 25th of November, 1818, to 

 the 12th of January, 1819. The first reappearance, calculated before- 

 hand by Encke, was observed by Rumker at Paramatta. (Galle, op. 

 cit., p. 215, 217, 221, and 222.) Biela's interior comet, or, as it is also 

 called, Biela's and Gambart's, was first seen by Montaigne on the 8th 

 of March, 1772 ; then by Pons on the 10th of November, 1805; after- 

 ward on the 27th of February, 1826, at Josephstadt in Bohemia, by Von 

 Biela ; and on the 9th of March by Gambart, at Marseilles. The ear- 

 liest rediscoverer of the Comet of 1772 is undoubtedly Biela, and not 

 Gambart; but, on the other hand, he calculated the elliptical elements 

 of its orbit earlier than Biela, and uearly at the same time as Clausen. 

 (Arago, in the Annuaire of 1832, p. 184 ; and in the Comptes Rendus, 

 torn. Hi., 1836, p. 415.) The first reappearance of Biela's Comet, cal- 

 culated beforehand, was observed by Henderson, at the Cape of Good 

 Hope, in October and December, 1832. The already mentioned won- 

 derful doubling of Biela's Comet by separation took place at its elev- 

 enth reappearance since 1772, at the end of the year 1845. (See Galle, 

 by Olbers, p. 214, 218, 224, 227, and 232.) 



