Observations on the Two Lately Discovered Celestial Bodies

PHILOSOPHICAL TRANSACTIONS. VIII. Observations on the two lately discovered celestial Bodies. By William Herschel, LL. D. F. R. S. Read May 6, 1802. In my early account of the moving star discovered by Mr. Piazzi, I have already shewn that it is of a remarkably small size, deviating much from that of all the primary planets.* It was not my intention to rest satisfied with an estimation of the diameter of this curious object, obtained by comparing it with the Georgian planet, and, having now been very successful in the application of the lucid disk micrometer, I shall relate the result of my investigations. But the very interesting discovery of Dr. Olbers having introduced another moving star to our knowledge, I have extended my researches to the magnitude, and physical construction, of that also. Its very particular nature, which, from the observations I shall relate, appears to be rather cometary * By comparing its apparent disk with that of the Georgian planet, it was estimated, that the real diameter of this new star could not amount to $\frac{3}{4}$ths of that of our moon. MDCCCII. than planetary, will possibly throw also considerable light upon the circumstances belonging to the other celestial body; and, by that means, enable us to form some judgment of the nature of both the two last-discovered phenomena. As the measures I have taken will oblige me to give a result which must appear extraordinary, it will be highly necessary to be particular in the circumstances of these measures, and to mention the condition and powers of the telescopes that were used to obtain them. Magnitude of the new Stars. April 1, 1802. Having placed a lucid disk at a considerable distance from the eye, but so that I might view it with perfect distinctness, I threw the image of Mr. Piazzi's star, seen in a 7-feet reflector, very near it, in order to have the projected picture of the star and the lucid disk side by side, that I might ascertain their comparative magnitudes. I soon perceived that the length of my garden would not allow me to remove the disk-micrometer, which must be placed at right angles to the telescope, far enough to make it appear no larger than the star; and, not having disks of a less diameter prepared, I placed the smallest I had, as far from me as the situation of the star would allow. Then, bringing its image again by the side of the disk, and viewing, at the same time, with one eye the magnified star, while the other eye saw the lucid disk, I perceived that Ceres, which is the name the discoverer has given to the star, was hardly more than one third of the diameter of the disk, and certainly less than one half of it. This being repeated, and always appearing the same, we shall not under-rate the size of the star, by admitting its diameter to have been 45 hundredths of the lucid disk. The power of the telescope, very precisely ascertained, by terrestrial geometrical measures properly reduced to the focus of the mirror on the stars, was 370,42. The distance of the lucid disk from the eye, was 2131 inches; and its diameter 3.4 inches. Hence we compute, that the disk was seen under an angle of 5' 29",09; and Ceres, when magnified 370 times, appearing, as we have shewn, 45 hundredths of that magnitude, its real diameter could not exceed 0",40. Had this diameter amounted to as much as was formerly estimated, the power of 370 would have made it appear of 6' 10", which is more than the whole lucid disk. This extraordinary result, raised in me a suspicion, that the power 370 of a 7-feet telescope, and its aperture of 6.3 inches, might not be sufficient to shew the planet's feeble light properly. I therefore adapted my 10-feet instrument to observations with lucid disks; which require a different arrangement of the head of the telescope and finder: I also made some small transparencies, to represent the object I intended to measure. April 21. The night being pretty clear, though perhaps not quite so proper for delicate vision as I could have wished, I directed my 10-feet reflector, with a magnifying power of 516,54, also ascertained by geometrical terrestrial measures reduced to the focus of the instrument on celestial objects, to Mr. Piazzi's star, and compared it with a lucid disk, placed at 1486 inches from the eye, and of 1.4 inch in diameter. I varied the distance of the lucid disk many times; and fixed at last on the above-mentioned one, as the best I could find. There was, however, a haziness about the star, which resembled a faint coma; and this, it may be supposed, must render the measure less satisfactory than it would otherwise have been. From these data we compute, that the disk appeared to the natural eye under an angle of $3' 14''$, while Ceres, when magnified $516\frac{1}{2}$ times, was seen by the other eye of an equal magnitude; and that consequently its real diameter, by measurement, was only $0''$.38. April 22. $11^h 38'$, sidereal time. I used now a more perfect small mirror; the former one having been injured by long continued solar observations. This gave me the apparent diameters of the stars uncommonly well defined; to which, perhaps, the very favourable and undisturbed clearness of the atmosphere might contribute considerably. With a magnifying power of $881,51$, properly ascertained, like those which have been mentioned before, I viewed Dr. Olbers's star, and compared it with a lucid disk of 1.4 inch in diameter, placed at 1514 inches from the eye, measured, like the rest of the distances, with long deal rods. The star appeared to me so ill defined, that, ascribing it to the eye-glass, I thought it not adviseable to compare the object, as it then appeared, with a well defined lucid disk. Exchanging the glass for that which gives the telescope a magnifying power of $516\frac{1}{2}$, I found Pallas, as the discoverer wishes to have it called, better defined; and saw, when brought together, that it was considerably less in diameter than the lucid disk. In order to produce an equality, I removed the disk to 1942 inches; and still found Pallas considerably less than the disk. Before I changed the distance again, I wished to ascertain whether Ceres or Pallas would appear under the largest angle, especially as the air was now more pure than last night. On comparing the diameter of Ceres with that of the lucid disk, I found it certainly less than the disk. By proper attention, and continued examination, for at least an hour, I judged it to be nearly \( \frac{3}{4} \) of the lucid disk. Then, if we calculate as before, it appears by this observation, in which there is great reason to place confidence, that the angle under which this star appeared, was only \( 0''.22 \). For, a lucid disk of 1.4 inch diameter, at the distance of 1942 inches, would be seen under an angle of \( 2' 28''7 \); three quarters of which are \( 1' 51''52 \). This quantity, divided by the power 516,54, gives \( 0'',2159 \), or, as we have given it abridged, \( 0'',22 \). \( 13^h 7' \). I removed the micrometer to the greatest convenient distance, namely, 2136 inches, and compared Dr. Olbers's star, which, on account of its great altitude, I saw now in high perfection, with the lucid disk. It was, even at this distance, less than the diameter of the disk, in the proportion of 2 to 3. When, by long continued attention, the appearance of Pallas was reduced to its smallest size, I judged it to bear no greater proportion to the diameter of the lucid disk of the micrometer, than as 1 to 2. In consequence of these measures, it appears that the diameter of Pallas, according to the first of them, is \( 0'',17 \); and, according to the last, where the greatest possible distinctness was obtained, only \( 0'',13 \). If it should appear almost incredible that these curious objects could give so small an image, had they been so much magnified as has been reported, I can say, that curiosity led me to throw the picture of Jupiter, given by the same telescope and magnifying power, on a wall at the distance of 1318 inches, of which it covered a space that measured 12 feet 11 inches. I do not mention this as a measure of Jupiter, for the wall was not perfectly at right angles to the telescope, on which account the projected image would be a little larger than it should have been, nor was I very attentive to other necessary minute circumstances, which would be required for an accurate measure; but we see at once, from the size of this picture, that the power of the telescope exerted itself to the full of what has been stated. As we generally can judge best of comparative magnitudes, when the measures are, as it were, brought home to us; it will not be amiss to reduce them to miles. This, however, cannot be done with great precision, till we are more perfectly acquainted with the elements of the orbits of these stars. But, for our present purpose, it will be sufficiently accurate, if we admit their mean distances from the sun, as the most recent information at present states them; for Ceres $2,6024$; and for Pallas $2,8$. The geocentric longitudes and north latitudes, at the time of observation, were, for Ceres, about $\varphi 20^\circ 4'$, $15^\circ 20'$; and for Pallas, $\varphi 23^\circ 40'$, $17^\circ 30'$. With these data, I have calculated the distances of the stars from the earth at the time of observation, partly by the usual method, and, where the elements were wanting, by a graphical process, which is sufficiently accurate for our purpose. My computed distances were $1,634$ for Ceres, and $1,8333$ for Pallas; and, by them we find, that the diameter of Ceres, at the mean distance of the earth from the sun, would subtend an angle of $0",35127$; and that, consequently, its real diameter is $161,6$ miles. It also follows, that Pallas would be seen, at the same distance from the sun, under an angle of $0",3199$; and that its real diameter, if the largest measure be taken, is $147$ miles; but, if we take the most distinct observation, which gives the smallest measure, the angle under which it would be seen from the sun, will be only $0''_{2399}$; and its diameter, no more than $110\frac{1}{3}$ miles. Of Satellites. After what has just now been shewn, with regard to the size of these new stars, there can be no great reason to expect that they should have any satellites. The little quantity of matter they contain, would hardly be adequate to the retention of a secondary body; but, as I have made many observations with a view to ascertain this point, it will not be amiss to relate them. Feb. 25. 20-feet reflector. There is no small star near Ceres, that could be supposed to be a satellite. Feb. 28. There is no small star within 3 or 4 minutes of Ceres, that might be taken for a satellite. March 4. $9^h 45'$, sidereal time. A very small star, south-preceding Ceres, may be a satellite. See Plate V. Fig. 1. where C is Ceres, S the supposed satellite, $a b c d e f$, are delineation stars, $c$ and $d$ are very small. S makes nearly a right angle with them; $e$ is larger than either $c$ or $d$. There is an extremely faint star $f$, between $e$ and $d$. $14^h 16''$. Ceres has left the supposed satellite behind. March 5. There are two very small stars, which may be satellites; see Fig. 2. where they are marked, 1st S, 2d S. The rest, as before, are delineation stars. March 6. The two supposed satellites of last night remain in their situation, Ceres having left them far behind. $10^h 16''$. There is a very small star, like a satellite, about $75^\circ$ south-following Ceres. See Fig. 3. It is in a line from C to $b$ of last night. 11\textsuperscript{h} 20\textsuperscript{'}.\ Ceres has advanced in its orbit; but has left the supposed satellite behind. March 30. 9\textsuperscript{h} 35\textsuperscript{'}.\ A supposed 1st satellite is directly following Ceres: it is extremely faint. A 2d supposed satellite is north-following. See Fig. 4. The supposed satellites are so small, that, with a 20-feet telescope, they require a power of 300 to be seen; and the planet should be hidden behind a thick wire, placed a little out of the middle of the field of view, which must be left open to look for the supposed satellites. 12\textsuperscript{h} 17\textsuperscript{'}.\ Ceres has changed its place, and left both the supposed satellites behind. March 31. 9\textsuperscript{h} 20\textsuperscript{'}.\ There is a very small star, on the north-preceding side of Ceres, which may be a satellite. 11\textsuperscript{h} 50\textsuperscript{'}.\ Ceres has moved forwards in its path; but the supposed satellite remains in its former situation. The nearest star is 20'' of time from Ceres; so that, within a circle of 40'' of time, there certainly is no satellite that can be seen with the space-penetrating power of this instrument. It is evident, that when the motion of a celestial body is so considerable, we need never be long in doubt whether a small star be a satellite belonging to it, since a few hours must decide it. May 1. 12\textsuperscript{h} 51\textsuperscript{'}.\ I viewed Pallas with the 20-feet reflector, power 300; there was no star within 3', that could be taken for a satellite. Of the Colour of the new Stars. Feb. 13.\ The colour of Ceres is ruddy, but not very deep. April 21.\ Ceres is much more ruddy than Pallas. April 22.\ Pallas is of a dusky whitish colour. Of the Appearances of the new Stars, with regard to a Disk. Feb. 7. Ceres, with a magnifying power of $516\frac{1}{2}$, shews an ill defined planetary disk, hardly to be distinguished from the surrounding haziness. Feb. 13. Ceres has a visible disk. April 22. In viewing Pallas, I cannot, with the utmost attention, and under the most favourable present circumstances, perceive any sharp termination which might denote a disk; it is rather what I would call a nucleus. April 28. In the finder, Pallas is less than Ceres. It is also rather less than when I first saw it. Of the Appearances of the new Stars, with regard to an Atmosphere, or Coma. April 21. I viewed Ceres for nearly an hour together. There was a haziness about it, resembling a faint coma, which was, however, easily to be distinguished from the body. April 22. I see the disk of Ceres better defined, and smaller, than I did last night. There does not seem to be any coma; and I am inclined to ascribe the appearance of last night to a deception, as I now and then, with long attention, saw it without; at which times, it was always best defined, and smallest. April 28. Ceres is surrounded with a strong haziness. Power 550. With $516\frac{1}{2}$, which is a better glass, the breadth of the coma beyond the disk may amount to the extent of a diameter of the disk, which is not very sharply defined. Were the whole coma and star taken together, they would be at least three times as MDCCCII. G g large as my measure of the star. The coma is very dense near the nucleus; but loses itself pretty abruptly on the outside, though a gradual diminution is still very perceptible. April 30. Ceres has a visible, but very small coma about it. This cannot be seen with low powers; as the whole of it together is not large enough, unless much magnified, to make up a visible quantity. May 1. The diameter of the coma of Ceres, is about 5 times as large as the disk, or extends nearly 2 diameters beyond it. $13^h\ 19'$. 20-feet reflector; power 477. The disk of Ceres is much better defined than that of Pallas. The coma about it is considerable, but not quite so extended as that of Pallas. May 2. $13^h\ 20'$. Ceres is better defined than I have generally seen it. Its disk is strongly marked; and, when I see it best, the haziness about it hardly exceeds that of the stars of an equal size. Memorandum. This may be owing to a particular disposition of the atmosphere, which shews all the stars without twinkling, but not quite so bright as they appear at other times. Jupiter likewise has an extremely faint scattered light about it, which extends to nearly 4 or 5 degrees in diameter. April 22. Pallas, with a power of $88\frac{1}{2}$, appears to be very ill defined. The glass is not in fault; for, in the day time, I can read with it the smallest letters on a message card, fixed up at a great distance. $13^h\ 17'$. The appearance of Pallas is cometary; the disk, if it has any, being ill defined. When I see it to the best advantage, it appears like a much compressed, extremely small, but ill defined, planetary nebula. April 28. Pallas is very ill defined: no determined disk can be seen. The coma about it, or rather the coma itself, for no star appears within it, would certainly measure, at first sight, 4 or 5 times as much as it will do after it has been properly kept in view, in order to distinguish between the haziness which surrounds it, and that part which may be called the body. May 1. Pallas has a very ill defined appearance; but the whole coma is compressed into a very small compass. $13^h\ 5'$. 20-feet reflector; power $477$. I see Pallas well, and perceive a very small disk, with a coma of some extent about it, the whole diameter of which may amount to 6 or 7 times that of the disk alone. May 2. $13^h\ 0'$. 10-feet reflector. A star of exactly the same size, in the finder, with Pallas, viewed with $516\frac{1}{2}$, has a different appearance. In the centre of it is a round lucid point, which is not visible in Pallas. The evening is uncommonly calm and beautiful. I see Pallas better defined than I have seen it before. The coma is contracted into a very narrow compass; so that perhaps it is little more than the common aberration of light of every small star. See the memorandum to the observation of Ceres, May 2. On the Nature of the new Stars. From the account which we have now before us, a very important question will arise, which is, What are these new stars, are they planets, or are they comets? And, before we can enter into a proper examination of the subject, it will be necessary to lay down some definition of the meaning we have hitherto affixed to the term planet. This cannot be difficult, since we have seven patterns to adjust our definition by. I should, for instance, say of planets, 1. They are celestial bodies, of a certain very 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. 7. Their orbits are at certain considerable distances from each other. Now, if we may judge of these new stars by our first criterion, which is their size, we certainly cannot class them in the list of planets: for, to conclude from the measures I have taken, Mercury, which is the smallest, if divided, would make up more than 135 thousand such bodies as that of Pallas, in bulk. In the second article, their motion, they agree perhaps sufficiently well. The third, which relates to the situation of their orbits, seems again to point out a considerable difference. The geocentric latitude of Pallas, at present, is not less than between 17 and 18 degrees; and that of Ceres between 15 and 16; whereas, that of the planets does not amount to one half of that quantity. If bodies of this kind were to be admitted into the order of planets, we should be obliged to give up the zodiac; for, by extending it to them, should a few more of these stars be discovered, still farther and farther deviating from the path of the earth, which is not unlikely, we might soon be obliged to convert the whole firmament into zodiac; that is to say, we should have none left. In the fourth article, which points out the direction of the motion, these stars agree with the planets. With regard to the fifth, concerning satellites, it may not be easy to prove a negative; though even that, as far as it can be done, has been shewn. But the retention of a satellite in its orbit, it is well known, requires a proper mass of matter in the central body, which it is evident these stars do not contain. The sixth article seems to exclude these stars from the condition of planets. The small comas which they shew, give them so far the resemblance of comets, that in this respect we should be rather inclined to rank them in that order, did other circumstances permit us to assent to this idea. In the seventh article, they are again unlike planets; for it appears, that their orbits are too near each other to agree with the general harmony that takes place among the rest; perhaps one of them might be brought in, to fill up a seeming vacancy between Mars and Jupiter. There is a certain regularity in the arrangement of planetary orbits, which has been pointed out by a very intelligent astronomer, so long ago as the year 1772; but this, by the admission of the two new stars into the order of planets, would be completely overturned; whereas, if they are of a different species, it may still remain established. As we have now sufficiently shewn that our new stars cannot be called planets, we proceed to compare them also with the other proposed species of celestial bodies, namely, comets. The criteria by which we have hitherto distinguished these from planets, may be enumerated as follows. 1. They are celestial bodies, generally of a very small size, though how far this may be limited, is yet unknown. 2. They move in very excentric ellipses, or apparently parabolic arches, round the sun. 3. The planes of their motion admit of the greatest variety in their situation. 4. The direction of their motion also is totally undetermined. 5. They have atmospheres of very great extent, which shew themselves in various forms of tails, coma, haziness, &c. On casting our eye over these distinguishing marks, it appears, that in the first point, relating to size, our new stars agree sufficiently well; for the magnitude of comets is not only small, but very unlimited. Mr. Pigott's comet, for instance, of the year 1781, seemed to have some kind of nucleus; though its magnitude was so ill defined, that I probably over-rated it much, when, November 22, I guessed it might amount to 3 or 4" in diameter. But, even this, considering its nearness to the earth, proves it to have been very small. That of the year 1783, also discovered by Mr. Pigott, I saw to more advantage, in the meridian, with a 20-feet reflector. It had a small nucleus, which, November 29, was coarsely estimated to be of perhaps 3" diameter. In all my other pretty numerous observations of comets, it is expressly remarked, that they had none that could be seen. Besides, what I have called a nucleus, would still be far from what I now should have measured as a disk; to constitute which, a more determined outline is required. In the second article, their motions differ much from that of comets; for, so far as we have at present an account of the orbits of these new stars, they move in ellipses which are not very excentric. Nor are the situations of the planes of their orbits so much unlike those of the planets, that we should think it necessary to bring them under the third article of comets, which leaves them quite unlimited. In the fourth article, relating to the direction of their motion, these stars agree with planets, rather than with comets. The fifth article, which refers to the atmosphere of comets, seems to point out these stars as belonging to that class; it will, however, on a more particular examination, appear that the difference is far too considerable to allow us to call them comets. The following account of the size of the comas of the smallest comets I have observed, will shew that they are beyond comparison larger than those of our new stars. Nov. 22, 1781. Mr. Pigott's comet had a coma of 5 or 6' in diameter. Nov. 29, 1783. Another of Mr. Pigott's comets had a coma of 8' in diameter. Dec. 22, 1788. My sister's comet had a coma of 5 or 6' in diameter. Jan. 9, 1790. Another of her comets was surrounded by haziness of 5 or 6' in diameter. Jan. 18, 1790. Mr. Mechain's comet had a coma of 5 or 6' in diameter. Nov. 7, 1795. My sister's comet had a coma of 5 or 6' in diameter. Sept. 8, 1799. Mr. Stephen Lee's comet had a coma of not less than 10' in diameter, and also a small tail of 15' in length. From these observations, which give us the dimensions of the comas of the smallest comets that have been observed with good instruments, we conclude, that the comas of these new stars, which at most amount only to a few times the diameter of the bodies to which they belong, bear no resemblance to the comas of comets, which, even when smallest, exceed theirs above a hundred times. Not to mention the extensive atmospheres, and astonishing length of the tails, of some comets that have been observed, to which these new stars have nothing in the least similar. Since, therefore, neither the appellation of planets, nor that of comets, can with any propriety of language be given to these two stars, we ought to distinguish them by a new name, denoting a species of celestial bodies hitherto unknown to us, but which the interesting discoveries of Mr. Piazzi and Dr. Olbers have brought to light. With this intention, therefore, I have endeavoured to find out a leading feature in the character of these new stars; and, as planets are distinguished from the fixed stars by their visible change of situation in the zodiac, and comets by their remarkable comas, so the quality in which these objects differ considerably from the two former species, is that they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes. It is owing to this very circumstance, that they have been so long concealed from our view. From this, their asteroidical appearance, if I may use that expression, therefore, I shall take my name, and call them Asteroids; reserving to myself, however, the liberty of changing that name, if another, more expressive of their nature, should occur. These bodies will hold a middle rank, between the two species that were known before; so that planets, asteroids, and comets, will in future comprehend all the primary celestial bodies that either remain with, or only occasionally visit, our solar system. I shall now give a definition of our new astronomical term, which ought to be considerably extensive, that it may not only take in the asteroid Ceres, as well as the asteroid Pallas, but that any other asteroid which may hereafter be discovered, let its motion or situation be whatever it may, shall also be fully delineated by it. This will stand as follows. Asteroids are celestial bodies, which move in orbits either of little or of considerable eccentricity round the sun, the plane of which may be inclined to the ecliptic in any angle whatsoever. Their motion may be direct, or retrograde; and they may or may not have considerable atmospheres, very small comas, disks, or nuclei. As I have given a definition which is sufficiently extensive to take in future discoveries, it may be proper to state the reasons we have for expecting that additional asteroids may probably be soon found out. From the appearance of Ceres and Pallas it is evident, that the discovery of asteroids requires a particular method of examining the heavens, which hitherto astronomers have not been in the habit of using. I have already made five reviews of the zodiac, without detecting any of these concealed objects. Had they been less resembling the small stars of the heavens, I must have discovered them. But the method which will now be put in practice, will completely obviate all difficulty arising from the asteroidical appearance of these objects; as their motion, and not their appearance, will in future be the mark to which the attention of observers will be directed. A laudable zeal has induced a set of gentlemen on the Continent, to form an association for the examination of the zodiac. I hope they will extend their attention, by degrees, to every part of the heavens; and that the honourable distinction which is justly due to the successful investigators of nature, will induce many to join in the meritorious pursuit. As the new method of observing the zodiac has already produced such interesting discoveries, we have reason to believe that a number of asteroids may remain concealed; for, how improbable it would be, that if there were but two, they should have been so near together as almost to force themselves to our notice. But a more extended consideration adds to the probability that many of them may soon be discovered. It is well known that the comas and tails of comets gradually increase in their approach to the sun, and contract again when they retire into the distant regions of space. Hence we have reason to expect, that when comets have been a considerable time in retirement, their comas may subside, if not entirely, at least sufficiently to make them assume the resemblance of stars; that is, to become asteroids, in which state we have a good chance to detect them. It is true that comets soon grow so faint, in retiring from their perihelia, that we lose sight of them; but, if their comas, which are generally of great extent, should be compressed into a space so small as the diameters of our two asteroids, we can hardly entertain a doubt but that they would again become visible with good telescopes. Now, should we see a comet in its aphelion, under the conditions here pointed out, and that there are many which may be in such situations, we have the greatest inducements to believe, it would be a favourable circumstance to lead us to a more perfect knowledge of the nature of comets and their orbits; for instance, the comet of the year 1770, which Mr. Lexell has shewn to have moved in an elliptical orbit, such as would make the time of its periodical return only about $5\frac{1}{2}$ years; if this should still remain in our system, which is however doubtful, we ought to look for it under the form of an asteroid. If these considerations should be admitted, it might be objected, that asteroids were only comets in disguise; but, if we were to allow that comets, asteroids, and even planets, might possibly be the same sort of celestial bodies under different circumstances, the necessary distinction arising from such difference, would fully authorise us to call them by different names. It is to be hoped that time will soon throw a greater light upon this subject; for which reason, it would be premature to add any other remarks, though many extensive views relating to the solar system might certainly be hinted at. Additional Observations relating to the Appearances of the Asteroids Ceres and Pallas. May 4, 12h 40'. 10-feet reflector; power 516$\frac{1}{2}$. I compared Ceres with two fixed stars, which, in the finder, appeared to be of very nearly the same magnitude with the asteroid, and found that its coma exceeds their aberration but in a very small degree. 12h 50'. 20-feet reflector; power 477. I viewed Ceres, in order to compare its appearance with regard to haziness, aberration, atmosphere, or coma, whatever we may call it, to the same phenomena of the fixed stars; and found that the coma of the asteroid did not much exceed that of the stars. H h 2 I also found, that even the fixed stars differ considerably in this respect among themselves. The smaller they are, the larger in proportion will the attendant haziness shew itself. A star that is scarcely perceptible, becomes a small nebulosity. 10-feet reflector. $13^h\ 10'$. I compared the appearance of Pallas with two equal fixed stars; and found that the coma of this asteroid but very little exceeds the aberration of the stars. $14^h\ 5'$, 20-feet reflector. I viewed Pallas; and, with a magnifying power of 477, its disk was visible. The coma of this asteroid is a little stronger than that which fixed stars of the same size generally have.