SECT, xxxvi.] LEXEL'S COMET. 389 



ascertained that in 1767 the comet must have passed Jupiter 

 at a distance less than the fifty-eighth part of its distance 

 from the sun, and. that in 1779 it would be 500 times nearer 

 Jupiter than the sun ; consequently the action of the sun on 

 the comet would not be the fiftieth part of what it would 

 experience from Jupiter, so that Jupiter became the primum 

 mobile. Assuming the orbit to be such as Lexel had deter- 

 mined in 1770, La Place found that the action of Jupiter, 

 previous to the year 1770, had so completely changed the 

 form of it, that the comet which had been invisible to us 

 before 1770 was then brought into view, and that the action 

 of the same planet, producing a contrary effect, has subse- 

 quently to that year removed it from our sight, since it was 

 computed to be revolving in an orbit whose perihelion was 

 beyond the orbit of Ceres. However, the action of Jupiter 

 during the summer of 1840 must have been so great, from 

 his proximity to that singular body, that he seems to have 

 brought it back to its former path as he had done in 1767, 

 for the elements of the orbit of a comet which was discovered 

 in November 1843, by M. Faye, agree so nearly with those 

 of the orbit of Lexel's comet that the two bodies were 

 supposed to be identical; by the subsequent computation 

 of M. Le Verrier, it appears, however, that they are not 

 the same, that they were both brought to our system by 

 Jupiter's attraction, and that they have been in it more than 

 a century, and have frequently come near the earth without 

 having been seen. From the smallness of the excentricity, 

 the orbit resembles those of the planets, but this comet is 

 liable to greater perturbations than any other body in the 

 system, because it comes very near the orbit of Mars when 

 in perihelion, and very near that of Jupiter when in 

 aphelion; besides, it passes within a comparatively small 

 distance of the orbits of the minor planets, and as it will 

 continue to cross the orbit of Jupiter at each revolution till 

 the two bodies meet, its periodic time, now about seven 

 years, will again be changed, but in the mean time it ought 



