nebulosity. We see it only in one direction out schel's delineations of 1824 and 1837, to the cirof an infinite number. May there not be some cumstance that the first was made in a bad climate, particular direction, in which it would appear a symmetrical formation, or if it is not a single whole, but a combination of separate formations, may there not be some direction in space along which its separate component parts would assume regular or symmetrical forms? and the second in a good one, and to regard a difference in the purity and homogeneity of the atmosphere, as equivalent to a difference in the size and power of the telescope. The drawing of 1837, may therefore be regarded as made with a telescope of much greater size than that with which the drawing of 1824 was made. A change in the health, and in the optical condition of the observer's * The variations of figure which this nebula presents in the delineations of it by different astronomers might lead a careless speculator to the opin-eye may account for apparent changes in forms ion that it has either undergone, or is undergoing, great and rapid changes. Sir John Herschel does not participate in such an opinion that are slightly luminous. Sir John Herschel's eye may in 1824 have begun to experience that remarkable change, to which this organ is subject between twenty-five and fifty years of age, and it may have not only recovered its original vigor, but acquired new power, when he used it at the Cape. The material differences which our author has signalized between the delineations of Dr. Lamontt in 1837, and his own in the same year, arising, we are persuaded, more from difference of climate, and from difference of vision, than from differences between the telescopes employed, may be considered as favorable to our views. "Comparing," says he, "only my own drawings, made at epochs (1824 and 1837) differing by 13 years, the disagreements, though confessedly great, are not more so than I am disposed to attribute to inexperience in such delineations (which are really difficult) at an early period-to the far greater care, pains, and time, bestowed upon the later drawings, and, above all, to the advantage of local situation, and the very great superiority in respect both of light and defining power in the telescope at the latter, over what it possessed at the former epoch, the reasons of which I have already mentioned. These The next remarkable object of which Sir John circumstances render it impossible to bring the fig- Herschel gives a minute drawing, and a detailed ures into comparison, except in points which could description, is 7 Argus, and the great nebula surnot be influenced by such causes. Now there is only rounding it. It is situated in R. Ascension, 10 one such particular on which I am at all inclined to 38′ 28′′, and in 148° 47′ of north polar distance. insist as evidence of change, viz., in respect of the Our author's drawing of it (17 inches by 12) has situation and form of the nebula oblongata,' which my figure of 1824 represents as a tolerably regular the same merit as that of the nebula in Orion, and oval, &c. &c. Comparing this with its present the nebula the same unmeaning and unintelligible appearance as exhibited in Plate VIII., it seems aspect. This nebula is regarded by Sir John as hardly possible to avoid the conclusion of some sensi- of all sidereal objects that which unites most points ble alteration having taken place. No observer now, of interest. "Its situation is very remarkable in I think, looking ever so cursorily at this point of the midst of one of those rich and brilliant masses, detail, would represent the broken, curved, and a succession of which curiously contrasted with unsymmetrical nebula in question as it is represented in the earlier of the two figures; and to suppose it dark adjacent spaces, (called by the old navagators seen as in 1837, and yet drawn in 1824, would argue coal-sacks,) constitute the Milky Way in that pormore negligence than I can believe myself fairly tion of its course which lies between the Centaur chargeable with.”—pp. 31, 32. and the main body of Virgo." In this part of the galaxy there is an average of 3138 stars in a Passing over another evidence of change, on which Sir John thinks, that "considerable stress square degree, and in the denser part 5093 in the might be laid," we have no hesitation in avowing, the midst of this vast stratum of stars, and is reThe bright star 7 Argus, stands in without regarding our author as in any way charge-markable for the singular change which its lustre able with negligence, that we cannot concur with has undergone since 1677. It was then a star of him in thinking that the discrepancies in question the fourth magnitude. In our recent_catalogues afford any proof whatever of a change in the nebit is a star of the second magnitude. In 1834 Sir ula. John Herschel found it brighter than a star of the second magnitude. In November, 1837, its magnitude was unchanged, but in December of that year he was astonished by its sudden increase of brightness, which exceeded even that of Rigel. In March, 1843, the Rev. W. S. Mackay of the Free Church Mission, Calcutta, observed a very remarkable in Such an extensive change as that to which he refers has no parallel in any of the sidereal phenomena, and would be equivalent to the creation and extinction of whole clusters of worlds and systems, within the brief interval of thirteen years! Had the apparent evidences of change been even more distinct and numerous, we should have exhausted every possible mode of accounting for these appearances, rather than have allowed ourselves to consider them as real. In comparing the nebular delineations of Lord Rosse, with those made with smaller instruments by Sir John Herschel, we never attribute the discrepancies to real changes in the nebula. In like manner we ought to ascribe the discrepancies between Sir John Her same area. crease in its lustre; it had become a star of the first magnitude, as bright as Canopus, and in color and size very much like Arcturus. In 1844 Mr. Maclear found it almost equal to Sirius. In 1845 *This figure is engraved in the memoirs of the Astronomical Society, vol. ii. + Published with his Thesis," Ueber die Nebelflecken." Munich, 1837, it had again begun to decline in lustre. The fol- | having constructed, on this principle, charts of the lowing is a list of these changes. After giving this summary of the magnitudes of Argus, Sir John Herschel remarks that— "A strange field of speculation is opened by this phenomenon. The temporary stars heretofore recorded have all become totally extinct. Variable stars, so far as they have been carefully attended to, have exhibited periodical alternations, in some degree at least regular, of splendor and comparative obscurity. But here we have a star fitfully variable to an astonishing extent, and whose fluctuations are spread over centuries, apparently with no settled period, and with no regularity of progression. What origin can we ascribe to these flashes and relapses? What conclusions are we to draw, as to the comfort and habitability of a system depending for its supply of light and heat on so uncertain a source?" -p. 36. As this nebula does not exhibit the slightest appearance of being resolvable into stars, it has therefore nothing in common with the Milky Way, on the ground of which it is projected, and may therefore, as our author supposes, be placed at an immeasurable distance behind that stratum. The accurate representation of this nebula, which includes no fewer than 1216 stars, and is represented in Plate IX. of the work before us, was a northern and southern hemispheres, divided into zones of 3° in breadth, or polar distance, and into hours of rigid ascension, he laid down the nebulæ in each, so as to obtain a coup d'œil of their distribution over the whole heavens. In this way, he was led to the following conclusions: "1st. The distribution of the nebulæ is not like that of the Milky Way, in a zone or band encircling the heavens. 66 2dly. One third of the whole nebulous contents of the heavens are congregated in a broad irregular patch, occupying about one eighth of the whole surface of the sphere, chiefly situated in the northern hemisphere, and occupying the constellations Leo, Leo Minor, the body, tail and hind legs of Ursa Major, the nose of the Camelopard, the point of the tail of Draco, Canes Venatici, Coma, the preceding leg of Bootes, and the head, wings, and shoulder of Virgo. This, for distinction, I shall call the nebulous region of Virgo. "3dly. Within this area there are several local centres of accumulation, where the nebulæ are exceedingly crowded, viz., first, from 59° to 62° of north polar distance in the 13th hour of right ascension between the northern part of Coma and the fore-legs of Chara, as also (in the same hour) and the northern wing of Virgo, and again in the from 72° to 78° N. P. D., between the palm branch same hour from 80 to 870 N. P. D., in the northern wing and breast of Virgo. "The general conclusion which may be drawn from this survey is, that the nebulous system is distinct from the sidereal, though involving, and perhaps to a certain extent mixing with the latter. The great nebulous constellation in the northern hemisphere, which I have called the region of Virgo, being regarded as the main body of this system, and work of great difficulty and labor. It occupied several months, during which our author often despaired of being able to transfer to paper its end-subtending at our point of view an angle of 80° or less details. No description is capable of conveying the least idea of its character, and we must therefore refer our readers to the engraved repre sentation of it. The magnificent catalogue of nebulæ and clusters of stars in the southern hemisphere comprehends 4015 of these objects, occupying about 80 closely printed pages. The whole of these observations, as well as the entire work of reducing, arranging, and preparing this and all the other catalogues, were executed by Sir John himself, and have more resemblance to the labor of a long life than to the work of a few years. Each of these objects is minutely described by means of single letters or abbreviations, as in the following example:-No. 4015, not v F; L; 1 E; g lb M; 60; which means not very faint; large; a little extended; gradually a little brighter in the middle; diameter 60"; so that if the descriptions had been printed in the ordinary manner, this catalogue would have filled a whole volume of the Philosophical Transactions. In order to ascertain the law of distribution of these nebulæ and clusters over the surface of the heavens in both hemispheres, Sir John adopted a projection which represented equal areas on the sphere by equal areas on the projection; and *"To execute this projection, we have only to take 90°, it is evident that, supposing its form to approach to the spherical, our distance from its centre must be considerably less than its own diameter, so that our system may very well be regarded as placed somewhat beyond the borders of its denser portion, yet involved among its outlying members."—pp. 135-6. In treating of the classification of nebulæ, our The regular nebulæ are distinguished by terms author divides them into regular and 'irregular. expressing their magnitude, brightness, roundness, condensation, and resolvability; and the irregular nebulæ are subdivided into subregular, compact, branching, convoluted, cellular, fissured, and cometic. The third class of these objects. named referred to the class of globular clusters, and are irregular clusters, are those which cannot be subdivided into three classes-1st, rich, brilliant, and conspicuous clusters; 2d, poor and inconsiderable clusters; and 3d, those which cannot be included in either of these divisions. Before concluding the subject of nebulæ and clusters of stars, Sir John Herschel treats of the Magellanic clouds, and gives fine eye-sketches of the two nubecula which compose them, drawn Sin. 30, Sin. 10, Sin. 1° 30, and so on to Sin. 5°, from a out upon any scale you please the successive values of table of natural sines, and these will be the radii of circles, corresponding in our projection to the successive polar distances, 1o, 2o, 3o, *'* * * 90°.” entirely without telescopic aid, when seated at a table in the open air, in the absence of the moon, and with no more light than was absolutely necessary for executing a drawing at all." Sir John was driven to this mode of delineating these interesting nubecula in consequence of all his own attempts to represent other than very small portions of the Nubeculæ Major in the telescope, having been completely baffled by the overwhelming perplexity of its details. Representations of these two nubeculæ, stated to be engraven from very correct drawings, have been published by Mr. Dunlop in the Philosophical Transactions for 1828, but they have little or no resemblance to the delineations of Sir John Herschel.* The Nubecula Minor lies between the parallels of 162° and 165° of north polar distance, and between the meridians of 0h 28m and 1h 15m right ascension. It is of a generally round form to the eye, and its centre of brightness coincides with its centre of figure. The magnificent globular cluster, 47 Toucani of Bode, precedes it by a few minutes of right ascension, but has no connection with it, and, as our author states, "with this exception, its situation is in one of the most barren regions of the heavens. The access to the nubecula minor on all sides is through a desert. Neither with the naked eye, nor with a telescope, is any connection to be traced either with the greater nubecula or with the Milky Way. Within its area there are 37 objects entitled to entry in the catalogue as nebula or clusters, and, altogether, 244 stars, nebulæ, and clusters, the positions of which have been determined as preparatory to the construction of a chart of the nubecula and the future execution of a drawing of it. reviewed the southern heavens with the 20 feet reflector, for the purpose of detecting close double stars. Hence, the catalogue of double stars is comparatively deficient in those of the first or closest class, whose distance is under two seconds. The numbers in the catalogue are a continuation of those in Sir John Herschel's 6th catalogue, published in the 9th volume of the memoirs of the Astronomical Society. They commence with No. 3347, and terminate with No. 5442, so that the catalogue, occupying 72 pages, contains 2095 double stars. This catalogue is followed by tabulated micrometical measures of double stars, with a synopsis of those measures, a comparison of angles of position of double stars measured with the 7 feet equatorial, and the 20 feet reflector, and with special remarks on the measures of particular double stars in the catalogue. The following is a brief notice of the stars thus specially referred to: λ Toucani. R. Asc. Oh 46m N. P. D. 160° 26'. Angle of position in 1835.92, 78° 30, 1837.74, 80° 35, indicating a pretty rapid angular rotation. h 2036. R. A. 1h 12m N. P. D. 106° 41, angle of position 1830.786, 53°; 1836.958, 38° 05′, giving an angular motion of -2° 422 per annum. p Eridani R. A. 1h 33m N. P. D. 147° 3'. Angle of position 1834.8, 120° 27′. 1836.723, 119° 30', indicating a considerable orbitual motion. 70. Dunlop. R. A. 8h 24m N. P. D. 134° 10'. Angle of position 1826.3, 20° 8' (Dunlop,) 1836.994, 351° 27′ (Herschel,) indicating a very rapid rotation. 8 Hydrae et Crateris. R. A. 11h 44m N. P. D. 122° 58', angle of position in 1834.47, 338° 3′, 1838.09, 342° 2′, indicating a motion in this fine double star of 1° 077 annually. The Nubecula Major is situated between the parallels of 156° and 162° N. P. D., and between a Crucis. R. A. 12h 17m N. P. D. 152° 9′. the meridians of 4h 40m and 6h 0m of R. Ascen- Distance of the stars 5" 65. This beautiful double sion. It consists, like the Minor, "partly of large star has excited the notice of all the more recent tracts and ill-defined patches of irresolvable neb-southern observers. Angle of position, 1826.45, ula, and of nebulosity in every stage of resolution, 114° 24′ (Dunlop) 1835.53, 120° 36', (Herschel,) up to perfectly resolved stars, like the Milky Way, giving an orbitual motion of-0° 698 annually, or as also of regular and irregular nebulæ, properly-0° 478, taking Sir John Herschel's observations so called, and globular clusters in every stage of by themselves. 66 resolvability, and clustering groups." It contains y Centauri. R. A. 12h 32" N. P. D. 138° 1'. no fewer than 278 of these objects, and altogether "The extreme dimness of this remarkably fine but 919 stars, nebulæ, and clusters. Our author is difficult double star-each equal, and each of the of opinion, that the Magellanic clouds are sys- fourth magnitude, necessarily renders the angles tems sui generis, which have no analogues in our of position precarious." Angle of position 1835hemisphere." .32, 351° 35', 1836.38, 357° 21', giving an angular motion of +5° 440 annually. The Second chapter of the work before us, on the Double Stars of the Southern Hemisphere, is doubtless of equal importance with the first, though the detection and measurement of these stars was regarded by our author as of subordinate interest, and therefore allowed to interfere as little as possible with the discovery of new nebulæ, and the determination of the places of those already known. It would have required at least ten years to have * The only mode of reconciling the delineations of the two astronomers, is to suppose that Mr. Dunlop used a telescope with a small magnifying power, exhibiting details which an eye-sketch could not contain. * y Virginis. R. A. 12h 23m N. P. D. 90° 31'. As the complete establishment of the elliptic motion of this interesting double star is justly deemed by our author one of the great facts of modern astronomy, he has reinvestigated its orbit, by a careful examination of all the recorded meas *Capt. Smith, in his Cycle of Celestial Objects, pp. 275-283, has given an admirable analysis of all the observations on this star previous to the southern ones of Sir John Herschel, with an orbit calculated from the Bedford observations, which yields a period of about 180 years, differing only 2° 12' from the new period of Sir J. Herschel. See this Journal, vol. vi., p. 234: ures. He was so fortunate as to observe, about | Henderson at one second, it will follow from what the end of 1835 and beginning of 1836, the eclipse has been said, that the real diameter of the relaas it were of the one star by the other, a phenom- tive orbit of one star about the other, cannot be so enon seen also by Capt. Smith at Bedford in Jan-small as that of the orbit of Saturn about the sun, uary, 1826. Sir John has now abandoned the and exceeds, in all probability, that of the orbit of large elliptical orbit which he obtained, and which Uranus." It must therefore be an object of the seemed to be rendered necessary in order to include highest interest with astronomers, to obtain a sucthe observations of Bradley and Mayer. By cession of the most accurate measures of the disrejecting these observations, and using only the tance of the two stars.* angles of position taken by the position-micrometer The importance of Astrometry, or the method for the epoch of 1781.89, when it was first measured of obtaining an accurate numerical expression of by Sir W. Herschel, and that of 1845.34, which the apparent magnitude of the stars, has been was taken by Capt. Smith, he obtained the follow-universally admitted by astronomers, for it is chiefing elements :ly by a comparison of these magnitudes at different epochs, that we can become acquainted with Eccentricity, 0.87952 Inclination to the plane of projection, 23° 35′ 40′′ changes that have taken place upon their surface, Position of ascending Node, Angular distance of Perihelion from 5° 33' passage, 313° 45' A. D. 1836.43 or ascertain the periods of their variation. Our limits will not permit us to describe the ingenious and admirable methods by which our author has endeavored to determine the comparative intensities of the light of the stars; but we shall givę the results in the following table, which contains the photometric determination of the comparative Her-intensities of the light of 69 stars, a Centauri being taken as the standard, and made 1.000: 182°12 years. Since this orbit was computed, Sir John schel has received from Mr. Maedler of Dorpat, the following measures of the angle of position Sirius of y Virginis, beside which we have placed the Canopus almost contemporaneous observations of English a Centauri observers, in order to show the degree of accuracy Arcturus which has now been attained in measuring the angle of position of two stars very near each other ; Rigel a Orionis A. D. 1841 355, Angles of position, 200° 6' a Eridani 34, Dawes 200° 3 Antares 0.404 1842. 361, according to 196° 11' Centauri 0.399 a Lupi 0.102 α Crucis 0.377 34, Airy a Phoenicis 0.101 197° 25' 1843. 349, Maedler, 66 33, Smith 1844. 356, a Aquilæ 192° 9' Spica 0.309 a Leporis 0.100 191° 36' Argus 0.262 8 Scorpii 0.098 188° 55' Fomalhaut 186° 57' Crucis 185° 24' a Centauri, R. A. 13h 42m. N. P. D. 122 9'. → Scorpii Orionis • Canis γ Crucis "This superb double star," says Sir J. Herschel, a Scorpii "beyond all comparison the most striking object a Trianguli of the kind in the heavens, and to which the dis- y Argus covery of its parallax, by the late Professor Hen-Gruis derson, has given a degree of astronomical im- Argus portance no less conspicuous, consists of two Argus individuals, both of a high ruddy or orange color, & Canis though that of the smaller is of a somewhat more • Orionis 9 Centauri sombre cast. They constitute together a star . Saggitarii which, to the naked eye, is equal or somewhat a Pavonis superior to Arcturus in lustre." The distance between the two stars has varied from 22".45, as observed by Sir Thomas Brisbane in 1824, to 16".12, as observed by Sir J. Herschel in 1837.44. Sir John is of opinion that the distance is decreasing at the rate of a little more than half a second annually, which, if continued, will bring on an occultation, or exceedingly close appulse, about the year 1867, The plane of the orbit passes nearly through our system. "Taking the coefficient of parallax of a Centauri," says our author, (not a Centauri, as misprinted in Mr. Henderson's paper,) as determined by Professor Argus In comparing the photometric results with the conventional scale of naked eye magnitudes, Sir John Herschel has found that if these conventional values be increased by the constant fraction 0.4142 * In concluding this notice of the southern double stars, we may mention that Mr. Mitchel, of the observatory at Cincinnati in the United States, has discovered that the fine star Antares is double. This important observation was made by means of an achromatic telescope, mounted parallactically, and executed at Munich by MM. Merz and Mahler. Its aperture is nearly twelve inches Eng lish.-Struve, Etudes Stellaires, note 64, p. 48. 0.207 Capricorni 0.088 0.198 (or No2—1,) the new scale of magnitudes so aris- | adding some curious speculations on its physical ing will represent the distances of the respective condition, and on that of comets in general. On stars, to which they are ascribed, from our system, the 29th October, its appearance was the most on the supposition of an intrinsic equality in the singular, and such as he had never observed in light of the stars themselves; that is, so that dif- any previous comet. Its nucleus small, bright, ferences of brightness shall be merely apparent, and highly condensed, was shielded or capped on and supposed to arise solely from differences of the side next the sun by a vivid but narrow cresdistance. Were this scale substituted for the cent of nebulous light, the front of which prepresent arbitrary one, "a Centauri," says our sented an outline nearly circular, with an ampliauthor, “would be our normal star of the first tude of about 90° from horn to horn. Within magnitude, Crucis of the second, a Orionis of this was situated the nucleus, but at a distance the third, v Hydra of the fourth, and 8 Volantis behind the front or vertex of the crescent, considof the fifth; and these are the magnitudes which erably less than its versed sine.* On the 1st of actually stand annexed to those stars in our cata- November it had the common appearance of a logues respectively. The effect of such a change comet, with its nucleus and slightly diverging tail; would be to place the nomenclature of magnitudes but on the 26th January, after its return from the on a natural, or, all events, on a photometric basis, sun, it had assumed a most surprising and totally easily remembered the relation between the Mag-new appearance. Its head was sharply terminated, nitude and the Light of any star being given by like a ground glass-lamp shade; and within this the simple equation, M2 L-1, a Centauri being head was seen a vividly luminous nucleus," like taken as the unit both of light and magnitude." a miniature comet. having a nucleus head and In our author's Fourth chapter, On the distri- tail of its own, perfectly distinct, and considerably bution of stars, and on the constitution of the exceeding in intensity of light the nebulous head." Galaxy in the Southern Hemisphere, he treats-As the comet rose higher, a minute bright point, first, of the statistical distribution of stars; second- never greater than 4", and like a small star, was ly, of the general appearance and telescopic distinctly perceived, and this point Sir John calls constitution of the Milky Way; and, thirdly, the nucleus. On the 25th January, the following on some indications of very remote telescopic measures were taken :branches of the Milky Way, or of an independent sidereal system or systems bearing a resemblance to such branches. The indications referred to under the third of these heads, are deduced from a phenomenon of a very interesting kind, which 66 66 Diameter of the comet's head in Diameter of the head in Decli 229".4 13h 38m 118".3 nation, Diameter of the head in R. As- 196".7 16h 25m Sir J. Herschel seems to have been the first to notice. It "consists in an exceedingly delicate and uniform dotting or stippling of the field of view by points of light too small to admit of any one being steadily and fixedly viewed, and too Diameter of the head in Declinanumerous for counting, were it possible so to view tion, 252" 16h 29m them." Our author was always satisfied of the The deficiency in this second measure of the reality of this phenomenon at the moment of ob-head obviously arose from the effect of twilight; servation, though the conviction was not perma- but we can only account for the increase in declinent, the idea of an illusion arising from physio-nation by concluding "that the change was real, and logical causes having subsequently arisen. Sir that the comet was actually increasing in dimenJohn has, however, given the right ascension and sions with such rapidity that it might almost be north polar distance of 37 points of the heavens said to be seen to grow!" M. Valz had pointed where this whiteness, or "stippling of the ground out the increase in the dimensions of comets as of the sky" was seen or suspected. In like manner, he has given the places of the points where the ground of the sky is perfectly dark or black, certainly devoid of any such stippling or nebulous phenomenon." and " On the 25th of October, 1837, Sir John was fortunate enough to obtain a view of the anxiously expected comet of Dr. Halley, and in his fifth chapter, occupying 21 pages, and constituting, in our opinion, one of the most interesting portions of his work, he has given his observations on this singular member of the solar system, illustrating them with thirteen beautiful drawings of it, and * Our author has represented in his thirteenth plate the course and aspect of the Southern Milky Way, from Antinous to Monoceres, delineated with the naked eye by faint lamp-light in the open air. they receded from the sun, but an increase in the ratio of 5 to 6, and in so short an interval, must be regarded as a different phenomenon. On the 26th, the nucleus appeared as a star of the 10th sions of the comet had greatly increased, the magnitude, furred and nebulous; and the dimendiameter in right ascension being 309", and in declination 329", so that the total bulk of the comet, exclusive of the coma, had greatly more than doubled in 24 hours. On the 28th January, upon looking through the 20 feet reflector, Sir John exclaims-" Most astonishing! The coma is all but gone, but there are long irregular nebulous tails in various directions." "The nucleus *This is no doubt Mr. Cooper's Fan, and M. Arago's "Sector." The tail was obliterated by the twilight, and subsequently appeared. |