COMETS. 



Comets, tcllites. Now, since the year 1770, neither Venus, the 

 *"— T m ^ 1 Earth, Mars, nor Jupiter, have suffered the smallest de- 

 rangement 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 con- 

 sider 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 force, by which they seem to have been sepa- 

 rated from a larger planet, (see Astronomy, p. 641,) 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 Pallas, are actually surrounded with 

 atmospheres of an immense size. The atmosphere of 

 Ceres is 675 English miles high, while that of Pallas 

 rises to the height of 468 miles. Now the height of any 

 of these atmospheres is greater than the united heights 

 of the atmospheres of all the other planets, and is above 

 a thousand times higher than it ought to have been, 

 according to the ratio which exists between the globes and 

 the atmospheres of all the other bodies of the system. 

 Astronomers were so forcibly struck with the magni- 

 tude of these atmospheres, that a dispute arose whether 

 Ceres and Pallas should be called planets or comets, 

 and the discussion terminated, by giving them the name 

 of asteroids, a class of bodies which were supposed to 

 partake of the nature both of planets and comets. But 

 to draw this argument still closer upon the subject, let 

 us enquire from what other source these atmospheres 



could be derived, if they were not imparted by the co- 

 met of 1770. If the four new planets are the frag- 

 ments of a larger body, endowed with an extensive at- 

 mosphere, each fragment woidd obviously carry off a 

 portion of atmosphere proportioned to its magnitude ; 

 but two of the fragments, Juno and Vesta, have no at- 

 mosphere at all, consequently the atmospheres of Ceres 

 and Pallas coidd not have been derived from the origi- 

 nal planet, but must have been communicated to them 

 at a period posterior to the divergency of the frag- 

 ments. 



It would have been a satisfactory addition to the pre- 

 ceding arguments, if we had been able to shew, by di- 

 rect calculation, that Ceres and Pallas v/ere at the same 

 instant with the comet in that part of their orbits which 

 was crossed by its path, and that the position of the 

 planes of the orbits was such, as to permit a near ap- 

 proximation. But as we have no data sufficiently cor- 

 rect for such a calculation, we must leave this part of 

 the subject to some future opportunity. There is one 

 fact, however, which in some measure supplies its place, 

 and which is therefore worthy of particular notice. The 

 nodes of the comet of 1770, lie exactly between the 

 nodes of Ceres and Pallas, an arrangement which is abso- 

 lutely indispensible to the truth of the preceding theory. 



We shall now conclude this article with three Tables, 

 containing lsV-The parabolic motion of comets in an 

 orbit, whose perihelion distance is equal to the mean 

 distance of the earth from the sun ; 2d, The parabolic 

 descent of comets towards the sun in a right line ; and, 

 3d, The elliptic motion of comets. Although these Ta- 

 bles occupy more room than we could have wished to 

 allot to this subject, yet as they were never before pub- 

 lished in any English work, and as they are extremely 

 useful and important to astronomers, we have present- 

 ed them in as abridged a form as possible. 



Comer?. 



Table I. Of the Parabolic Motion of a Comet, whose Perihelion Distance is equal to the Radius of the. 



Earth's Orbit. 



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