glimpses; but the star b retains its former light. Nebulous Appearance of the Comet. Dec. 6. The head of the comet, viewed with a mirror of twenty-four inches diameter, resenibles now one of those nebule, which in my catalogues would have been described, "a very large, brilliant, round nebula, suddenly much brighter in the middle." Dec. 16. Seven-feet reflector. The night being fine, and the moon not risen, the comet resembles a very bright, large, irregular, round nebula, very gradually much brighter in the middle, with a faint nebulosity on the south-preceding side. 66 Jan. 1, 1808. Seven-feet. Very bright, very large, very gradually much brighter in the middle." If I had not known this to be a comet, I should have added to my description of it as a nebula, that the centre of it might consist of very small stars; but this being impossible, I directed my ten-feet telescope with a high power to the comet, in order to ascertain the cause of this appearance; in consequence of which I perceived several small stars shining through the nebulosity of the coma. Jan. 14. Seven feet. Bright, pretty large, irregular round, brighter in the middie." Feb. 2. Ten-feet, twenty-four-inch aperture. "Very bright, large, irregular round, very gradually much brighter in the middle." There is a faint diffused ncbulosity on the north preceding side; I take it to be the vanishing remains of the comet's tail. Feb. 19. Considerably bright; about 4th of the field=3′ 26"" in diameter, gradually brighter in the middle." The faint nebulosity in the place where the tail used to be, still projects a little further from the centre than in other directions. Feb. 21. Less bright than on the 19th; nearly of the same size : gradually brighter it the middle. The nebulosity still a little. projecting on the side where the tail used to be. Result of the foregoing Observations. From the observations which are now before us, we may draw some inferences, which will be of considerable importance with regard to the information they give us, not only of the size of the comet, but also of the nature of its illumination. A visible, round, and well defined disk, shining in every part of it with equal brightness, elucidates two material circumstances; for since the nucleus of this comet, like the body of a planet, appeared in the shape of a disk, which was experimentally found to be a real one, we have good reason to believe that it consists of some condensed or solid body, the magnitude of which may be ascertained by calculation. For instance, we have seen, that its apparent diameter, the 19th of October, oh. 20', was not quite so large as that of the third satellite of Jupiter. In order there fore to have some idea of the real magnitude of our comet, we may admit that its diameter at the time of observation was about 1", which certainly cannot be far from truth. The diameter of the third satellite of Jupiter, however, is known to have a permanent disk, such as may at any convenient time be measured with all the accuracy that can be used; and when the result of such a measure has given us the diameter of this satellite, it may by calcu lation be brought to the distance from the earth at which, in my observation, it was compared with the diameter of the comet, and thus more accuracy, if it should be required, may be obtained. The following result of my calculation, however, appears to me quite sufficient for the pur pose of general information. From the perihelion distance 0·647491, and the rest of the given elements of the comet, we find, that its distance from the ascending node on its orbit at the time of observation was 73° 45′ 44′′; and having also the earth's distance from the same node, anti the inclination of the comet's orbit, we compute by these data the angle at the sun. Then by calculating in the next place the radius vector of the comet, and having likewise the distance of the earth trom the sun, we find by computation, that the distance of the comet from the earth at the time of observation was 1:169192, the mean distance of the earth being 1. Now since the disk of the comet was observed to subtend an angle of 1", which brought to the mean distance of the earth gives 1′∙169, and since we also know that the earth's diameter, which, according to Mr. Dalby, is 7913-2 miles*, subtends at the same distance an angle of 17"-2, we deduce from these prin ciples the real diameter of the comet, which is 538 miles. Having thus investigated the magnitude of our comet, we may in the next place also apply calculation to its illumination. The observations relating to the light of 1 the comet were made from the 4th of October to the 19th. In all which time the comet uniformly preserved the appearance of a planetary disk fully enlightened by the sun it was every where equally bright, round, and well defined on its borders. Now as that part of the disk which was then visible to us could not possibly have a full illumination from the sun, I have calculated the phases of the comet for the 4th and for the 19th: the result of which is, that on the 4th the illumination was 119° 45' 9", and that on the 19th it had gradually increased to 124° 22′ 40′′. Both phases appear to me sufficiently defalcated, to prove that the comet did not shine by light reflected from the sun only; for, had this been the case, the deficiency, I think, would have been perceived, not withstanding the smallness of the object. Those who are acquainted with my experiments on small silver globules will easily admit, that the same telescope which could show the spherical form of balls, that subtended only a few tenths of a second in diameter, would surely not have represented a cometary disk as circular, if it had been as deficient as are the figures which give the calculated appearances. If these remarks are well founded we, are authorised to conclude, that the body of the comet on its surface is self-luminous, from whatever cause this quality may be derived. The vivacity of the light of the comet also had a much greater resemblance to the radiance of the stars, than to the mild reflection of the sun's beams from the moon, which is an additional support to our former inference. The changes in the brightness of the small stars, when they are successively immerged in the tail or coma of the comet, or clear from them, prove evidently, that they are sufficiently dense to obstruct the free passage of star-light. Indeed if the tail or coma were composed of particles that reflect the light of the sun, to make them visible we ought rather to expect that the number of solid reflecting particles, required for this purpose, would entirely prevent our seeing any stars through them. But the brightness of the head, coma, and tail alone, will sufficiently account for the observed changes, if we admit that they shine not by reflection, but by their own radiance; for a faint object projected on a bright ground, or seen through it, will certainly appear somewhat fainter, although its rays should meet with no obstruction in coming to the eye. Now, as in this case we are sure of the bright interposition of the parts of the co met, but have no knowledge of floating particles, we ought certainly not to ascribe an effect to a hypothetical cause, when the existence of one, quite sufficient to explain the phenomena, is evident. If we admit that the observed full illumination of the disk of the comet cannot be accounted for from reflection, we may draw the same conclusion, with respect to the brightness of the head, coma, and tail, from the following consideration. The observation of the 2d of February mentions, that not only the head and coma were still very bright, but that also the faint remains of the tail were visible; but the distance of the comet from the Earth, at the time of observation, was nearly 240 millions of miles*, which proves, I think, that no light reflected from floating particles could possibly have reached the eye, without supposing the number, extent, and density of these particles far greater than what can be admitted. My last observation of the comet, on the 21st of February, gives additional support to what has been said; for at the time of this observation the comet was almost 2.9 times the mean distance of the sun from the earth t. It was also nearly 2.7 from the sun . What chance then could rays going to the comet from the sun, at such a distance, have to be seen after reflection, by an eye placed at more than 275 millions of miles § from the conet? And yet the instant the comet made its appearance in the telescope, it struck the eye as a very conspicuous object. The immense tails also of some comets that have been observed, and even that. of the present one, the tail of which, on the 18th of October, was expanded over a space of more than nine millions of miles, may be accounted for more satisfactorily, by admitting them to consist of radiant matter, such as, for instance, the aurora borealis, than when we unnecessarily ascribe their light to a reflection of the sun's illumination thrown upon vapours supposed to arise from the body of the comet. By the gradual increase of the distance of our comet, we have seen, that it assumed the resemblance of a nebula; and it is certain, that had I met with it in one 239894939. The sun's mean distance being 1, that of the comet was 2.89797. The comet's distance from the sun was 2.633196. 275077889. 9160542. of my sweeps of the zones of the heavens, as it appeared on either of the days between the 6th of December and the 21st of February, it would have been put down in the list I have given of nebulæ. This remark cannot but raise a suspicion, that some comets may have actually been seen under a nebulous form, and as such have been recorded in my catalogues; and were it not a task of many years' labour, I should undertake a review of all my nebulæ, in order to see whether any of them were wanting, or had changed their place; which certainly would be an investigation that might lead to very interesting con clusions. LIST OF NEW PUBLICATIONS IN FEBRUARY. 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They may be used in any situation, and are equally adapted for the manufac tory and drawing room. They are also very simple, readily managed, and capa ble of assuming the most elegant forms, test. Remarks. We cannot help observing that Mr. Seward has claimed more than he can well defend, if put to the From the figures attached to the specification, we are pretty certain that the shape of the chimney has no claim to novelty; nor is there sufficient novelty in the mode of supporting it, to justify an exclusive claim. We heartily concur with him in recommending the chimney to be of roughened glass. MR. SAMUEL CRACKLES (KINGSTON UPON He takes bone, which comes from the mouth of the whale, and having cut it into lengths of nine, twelve, or eighteen inches, boils or steeps it in water for such a length of time, as the nature of it may require, to make it soft and flexible. In this state it may be cut with a plane, knife, or other sharp instrument, into thin shavings, slices, or substances, which may be split, cut, or torn, by having lances fixed in front of the plane, knife, &c. into small pieces resembling bristles of all sizes, and degrees |