106 A Calcukition of the Orh'it of the Comet, 



one and the same comet. For however appearances iu 

 other respects may be, the eccentricity, or that which is 

 nearly commensurate with it, (perihelion distance,) is 

 the most material element by which tlie identit}^ of their 

 orbits could be ascertained. Though this comet may 

 have made one or more revolutions about the sun, since 

 astronomers have begun to watch the motions and ap- 

 pearances of comets, there is reason to believe, that it 

 has hitherto escaped their observations ; for, in m.ost 

 situations of the earth in its orbit, the comet could not 

 have much elevation above the horizon of places of any 

 considerable latitude in the northern hemisphere, so as 

 to be seen out of the effulgence of the sun's rays, till it 

 had so far passed the perihelion, as to be scarcely distin- 

 guished from other celestial bodies, by its splendor, or 

 crinited appearance. 



Compared with some comets, whose tails have ex- 

 tended from 70 to 120 degrees over the horizon, that of 

 this comet was by no means remarkable. The extent, 

 at most, v/as not more than 8 or 10 degrees, when first 

 observed, though the comet, at that time, had passed its 

 perihelion, and its situation was such as to cause a great 

 extension of its coma, or the atmosphere of its head. 

 This coma appeared to be very thick about the nucleus, 

 and its opacity much diminished the light of the star, 

 which much resembled the dimness of Saturn. The ap- 

 parent diameter of the comet's head was much greater 

 than could be expected in one of so little splendor, and 

 at so great a distance from the earth. Though I had no 

 means of measuring it, I am confident, that it exceeded 

 ' in this, many great comets, such as those of 1680, 1759, 

 and 1769; for these, though remarkable for the length 

 and splendor of their tails, were by no means so, on ac- 

 count of the size or magnitude of their heads'. There 

 were no other phenomena, peculiar to this cometj which 

 came under my observation. 



Since the discovery of those principles of motion, and 

 gravitation, which regulate the heavenly bodies in their 

 revolutions, the orbits of comets have been calculated 

 with much precision, as it respects that part of them, 

 which lies near the sun and earth. The principal desid€-- 



