274 Notice of the Periodical Comet of 1819. 



ed itt 1795 and 1786. According to this conjecture its timfe 

 of revolution can be only a very short period, and it is indis- 

 pensably necessary to have regard to the ellipticity of its orbit 

 in the calculation of its elements ; this is done by M. Encke, 

 astronomer at Gotha. The elliptic elements which he deter- 

 mined, either from the observations of 1805, or those of 1818, 

 differ from each other still less than the parabolic elements, 

 and there is no longer any doubt that they belong to the same 

 body, the periodic time being nearly three years and a half. 

 It has performed since its first appearance in 1805 four en- 

 tire revolutions, and returned to its perihelion at the com- 

 mencement of 1819. If we regard only the shortness of its 

 successive revolutions this body might be considered a planet ; 

 but it has continued to be classed among comets on account 

 of the appearance it presents, and its not being visible to us in 

 all parts of its orbit. To facilitate the observation of its re- 

 turn in 1822, M. Encke proposed to calculate an ephemeris 

 relative to that epoch ; but as the comet was for a great part 

 of this new revolution at a very small distance from Jupiter, 

 he was obliged to calculate the perturbations produced by the 

 disturbing force of that planet, and he found, in fact, that, in 

 consequence of this principal action, the time of anomalistic 

 revolution, the mean duration of which had been about 1204 

 days, from 1805 to 1819, would be augmented by about nine 

 days in the following revolution. He announced that in 1822 

 the comet, in consequence of its declination, would not be vi- 

 sible in Europe, and that, in order to observe it, it would be 

 necessary to go into the southern hemisphere. The event has 

 completely verified this prediction. The comet returned to 

 its perihelion in the latter part of May 1822. The elliptic 

 elements deduced from this re-appearance agree in the most 

 satisfactory manner with those calculated by M. Encke before 

 the appearance of the comet, according to former observations, 

 making allowances for irregularities produced by disturbing 

 forces. Although this important calculation of M. Encke was 

 well known, the academy which awarded to him, three years 

 ago, the astronomical prize, founded by La Lande, we have 

 thought it proper to mention the principal results before we 



