199 coSiMos. 



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

 iiscovery of Encke's Comet=^ 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 Villarceau has also 

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

 Astron. Nadir., 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 Bianpain, 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 ofBrorsen's Comet alone is very considerable, 



* The short period of revohitioii 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 18i22, 

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

 the accelerated I'evolution. Encke's Vierte Abhandlburg in the Schrif- 

 ten der Berl. Akademie for the year 1844. (Compare Arago, in the An- 

 nnaire for 1832, p. 181 ; in the Lettre a M. Adexandre 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 Mechain on the 17th of January, 1786; then by Miss Carolinrj 

 Herschel from the 7th to the 27th of November, 1795; afterward b^f 

 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 iu 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 Riimker at Paramatta. (Galle, op. 

 lit., 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 nearly at the same time as Clausen. 

 (AragO; in the Anmiaire of 1832, p. 184 ; and in the Comptes Rendus 

 tom. iii., 1836, p. 415.) T\\e fir.ft reappearance of Biela's Comet, caU 

 ciliated 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 a1 its elev 

 enth reappearance since 177i, at the end of the year 1845. (See Galle 

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



