6 HISTORY OF 



constant circuits at different distances, each taking up a time to 

 complete its revolutions proportioned to the greatness of the circle 

 which it is to describe. The lesser planets also, which are atten- 



ru rious. It is thus stated : " A comet appeared in the year mO, and was 

 carefully observed for nearly four mouths by M. Messier. When Prospc-rin 

 and Piugre applied themselves to calculate the elements of its orbit, they 

 tound that a parabolic path would not represent the observations of Messier, 

 and hence they suspected that its orbit might be sensibly elliptical. M. Lexell 

 of St Petersburgh computed its elements in an elliptical orbit, and he found 

 that its period was five years and a half, and that its greatest distance from 

 the sun did not much exceed that of Jupiter. This curious subject was in. 

 vestigated rather unsuccessfully by Slop, Sejour, and Lambert ; and a few 

 years ago it attracted the particular notice of the National Institute of France. 

 At the request of that learned body, Dr Biirekhardt repeated all the calcula- 

 tions with the utmost care, and the result of his investigations was a com. 

 plete confirmation of Lexell's conclusions. Here then is a most singular 

 anomaly in the motion of this comet. While all the other comets which have 

 been observed, move in orbits stretching far beyond the limits of the solar 

 system, and revolve in periods of long duration, the comet of 1770 never wan- 

 ders beyond the orbit of Saturn, and completes its revolution in the short 

 period of five years and a half. The return of this body, therefore, was con- 

 fidently expected by astronomers; but though it must now have completed 

 nearly eight revolutions round the sun, and though more observations have 

 been made in the heavens during the last 40 years than perhaps during the 

 two preceding centuries, yet the comet of 1770 has never re-appeared. We 

 are consequently entitled to conclude, that the comet of 1770 is lost, which 

 could happen only from its uniting with one of the planets, whose orbits it 

 crossed. Now, if such a union took place, two consequences would obviouely 

 flow from it. The planet would suffer a sensible derangement in its motions, 

 and its atmosphere would receive a vast accession of that nebulous matter, 

 of which the comets are often wholly composed. Here, then, we have two 

 distinct criteria to enable us to ascertain the individual planet by which the 

 comet was attracted. The path of the comet intersects the orbits only of 

 Venus, the Earth, Mars, the four new planets, and Jupiter, and therefore it 

 must have united with one of these bodies, or with their satellites. Now, 

 eince the year 1770, neither Venus the Earth, Mars, nor Jupiter, have suf- 

 fered the smallest derangement of this kind, nor have they received any visi. 

 ble addition to their atmospheres, We must, therefore, look to the four new 

 planets for some indication of the presence of a comet, and if they exhibit 

 any phenomena that are unequivocally of this description, we must consider 

 such a coincidence as a strong proof of the theory, or as one of the most 

 wonderful facts in the history of science. Two of the new planets, Ceres 

 , and Pallas, exhibit, in the form and position of their orbits, evident marks 

 of some great derangement ; but as this may have arisen from that explosive 

 lorve, by which they seem to have been separated from a larger planet, we 

 are not entitled to regard it as a proof of the present theory. But though 

 we cannot employ our first criterion either for or against the theory, the 

 second applies with irresistible force, and we would entreat the particular 

 attention of our readers to this single point. The two planets Ceres and 

 I'allas, are actually aurrouo ieil with atmospheres of an immense size. Tha 



