276 On Encke's Comet. 



such verj evident marks of an elliptical motion, that its peri- 

 odical revolution could thence be ascertained to a considerable 

 degree of accuracy, and it was found, by a careful examination 

 of all the observations, to be nearl}' of the same length as that 

 of Halley's comet; though in other respects the two orbits 

 are vei-y different from each other. 



We have now to add to the list another comet, still more 

 remarkable, on account of the shortness of its revolution, 

 which is only one thousand two hundred and five daj's. It had 

 been observed in 1786, 1795, and 1805; but the defects of the 

 observations in 1 786 and 1 795 had prevented its identity from 

 being noticed, until its appearance in 1819, when its elliptical 

 motion was discovered by Professor Encke. The details and 

 calculations relative to this remai'kable discoveiy are given in 

 three papers published in Bode's Astronomisches Jahrbuch for 

 1823, the titles of which are as follow: " A remarkable astro- 

 nomical discoi'eri/, and observations of the comet ofjulij 1819;" 

 by Dr. Olbers ; " On a remarkable comet xc/iich has probablj/ 

 a periodical revolution of about three years" by Professor 

 Encke ; and " On the Orbit of Pons's Comet, xi:ith the compicta- 

 tion of its apparent path for the time of its next appearance in 

 1822;" by Professor Encke. 



The first of these papers contains exti'acts fi-om letters of Dr. 

 Olbers, in which he commimicates his observations on tlie great 

 comet, visible by the naked eye in Europe and in this country, 

 in July 1819; together with his calculations of the parabolic ele- 

 ments of its orbit, which agree very nearly with those made 

 and published in this countr}-. He also mentions, with great 

 brevity, his discovery of the identity of the comet of 1 786 

 and 1795, with the small [or Encke's] comet of 1819. 



The second paper contains a full account of the calculations 

 of Professor Encke, to determine the orbit of this comet. He, 

 very modestly, names it Pons' comet, fi"om the circumstance 

 that Mr. Pons first discovered it, both in 1805 and in 1819; 

 but Professor Bode prefers to call it Encke's comet, after the 

 name of the discoverer of the true orbit; in like manner as 

 was done in the case of Halley and Olbers ; and it is highly 

 probable that this last name will be adopted by astronomers. 



When this comet was discovered at Marseilles by M. Pons, 

 on the 26th of November 1819, it was in the neck of the con- 

 stellation Pegasus. It appeared tolerably brigliT^ and anupleus 

 was several times perceived, but no appearance of a taO. It 

 was not observed in Germany till December 22, 1818, and 

 continued visible till January 12, 1819, describing in its course 

 an apparent arch of about twenty-three degrees. 



In calculating tlie parabolic orbit of this comet. Professor 



Encke 



