Page:Proceedings of the Royal Society of London Vol 1.djvu/101

Rh of a considerable size; 2. They move in not very excentric ellipses round the sun ; 3. The planes of their orbits do not deviate many degrees from the plane of the earth’s orbit; 4. Their motion is direct; 5. They may have satellites or rings ; 6. They have an atmosphere of considerable extent, which, however, bears hardly any sensible proportion to their diameters; and lastly, Their orbits are at certain considerable distances from each other.

These characters being next applied to the new stars, we ﬁnd, in the ﬁrst place, that as to the magnitude, they can certainly not be classed among planets; since the least of these (Mercury) is no less than 73,839 times larger than Pallas; 2. Their motions may perhaps agree sufﬁciently; but 3. The planes of the orbits of the new stars appear to deviate so much from that of the earth, that, were they admitted into the number of planets, we should have to extend the zodiac far beyond its present limits; and as it is not improbable that more of these bodies will be hereafter discovered, we shall perhaps end in having no zodiac at all. As to the 4th article, The motion of the new stars appears to be direct, like that of the planets. 5. Besides that no satellites have as yet been discovered belonging to these new stars, it may be inferred d priori that they have not a sufﬁcient mass of matter to retain any. 6. The new stars, with respect to the small comas they exhibit, differ widely from planets, and might rather be classed among the comets, did not other circumstances militate against this opinion; and lastly, The orbits of the new stars are so near each other, that the admitting them as planets would materially affect the general harmony that takes place among the rest. As to their being comets, the ﬁve following criteria are here given, by which those desultory bodies have hitherto been distinguished :— 1. They are generally of a very small size; 2. They move in very excentric ellipses, or apparently parabolic arches round the sun ; 3. The direction of their motion is totally undetermined; 4. The planes of their orbits admit of the greatest variety in their situation; and 5. They have atmospheres of very great extent, which show themselves in various forms of tails, comas, haziness, &c. On apply- ing these distinguishing characters to the new stars, we ﬁnd, that as to size, they might perhaps be classed with comets; but that, as to the nature of the curve in which they move, the direction of their motion, and the planes of their orbits, they deviate still more from comets than they do from planets; and that, as to their atmosphere, though they bear in this respect a greater resemblance to comets than to planets, yet, upon a careful cmnparison with the appearances of several comets observed of late years, it seems evident that they are not entitled to a place among them; the most considerable of their comas being barely one-ﬁftieth part of the smallest that has ever been observed to attend a comet.

Thus it appears, that neither the appellation of planet nor comet can be assigned to these newly discovered bodies. And it remains, therefore, to ﬁnd out some new term by which they may be distinguished. Previously to this, the author thinks it necessary to ﬁx