the Comet of 1811. 345 



This cornet came to us, from the regions of the fouth. 

 [t croffed the ecliptic on the 1 1th of July, and advanc- 

 ed fo far to the north, that on the '28th of September, 

 it was within the circle of perpetual apparition of this 

 atitude, and, of courfe, continued above the horizon, 

 :he whole 24 hours. In two or three days from this, 

 t reached its greatefl northern decHnation, about 50 

 degrees ; and then began to return towards the equa- 

 :or. But it did not attain its highcft geocentric lati- 

 tude, till the middle of October. Its apparent place 

 kvas then, within 28 degrees of the pole of the ecliptic, 

 .ts motion as feen from the earth, was, during the months 

 3f September and October, nearly in the arc of a great 

 :ircle. But the latter part of the time, in which it 

 ivas vifible, it fenfibly deviated to the eail of its form- 

 er direction ; though, on account of its moderate an- 

 gular velocity, its elongation from the fun was then 

 rapidly diminiihing. The rate of its apparent motion 

 !ias been lefs, than that of many other comets. One 

 feen in 1472 moved 40 degrees, and another in 1770, 

 l;5° in 24 hours. But the progrefs of the late comet 

 lever exceeded two degrees in 24 hours : and during 

 ;he latter part of the time, it did not amount to half 

 a, degree. 



This is a general view, of the apparent motion of 

 ihe comet, to a fpeclator on the earth. But its real mo- 

 tion will be found to be widely different : fo much fo, 

 that, while the apparent motion was, moft of the time, 

 towards the eaft ; its real motion in longitude was weft- 

 ward, or contrary to the order of the iigns. To de- 

 termine the direction and rate of this motion, it was 

 necelfary to refer it to the sun^ as a centre, and to cal- 

 culate the elements of the comet's orbit. Thefe are the 

 perihelion dijiance^ the time of paffing the perihelion, 

 the longitude of the perihehon, the longitude of the 

 node^ and the inclination of the orbit to the ecliptic. 

 To obtain a firft approximation, to the time and diftance 

 of the perihelion, fome of the early obfervations were 

 made ufe of. But for the final correclions, it was ne- 



