ments and periods of binary systems, which now | have happened among the fixed stars since the time

longs, and near the centre of which it is placed. [not been confirmed by subsequent observers. The We regret that we cannot allow ourselves to adopt nebular hypothesis to which they led, and which

has been carried to such an unwarrantable extent in our own day, has been refuted by the discoveries of the Earl of Rosse; and there is reason to believe that it has been renounced by Sir John Herschel himself.*

this noble and ingenious speculation; and there is sufficient evidence to induce us to believe, as the celebrated Russian astronomer, M. F. G. W. Struve, has stated, that Mr. Herschel himself was obliged to abandon it. He found, even with his largest telescope, that the Milky Way could not be The interesting subject of the Construction of sounded; and as the same uncertainty prevails the Heavens was pursued by Dr. Herschel during respecting the limits of the visible stars in all other the rest of his life, and his observations are recorded directions of the celestial vault, M. Struve draws in ten memoirs published in the Philosophical the conclusion, that "if we regard all the fixed Transactions for 1791, 1794, 1796, 1799, 1802, stars that surround the sun as forming a great sys-1806, 1811, 1814, 1817, and 1818. tem-that of the Milky Way-we are perfectly ignorant of its extent, and cannot form the least idea of this immense system." Having, therefore, no visible limits, it cannot be regarded as a nebula, according to the hypothesis of Mr. Herschel. But though the Milky Way is a system whose form and extent is not, and probably never will be, determined, yet, as Struve observes, there is evidently a certain law of condensation towards a principal plane, which law he has endeavored to determine. Lambert had imagined that the deviation of the Milky Way from the form of a great circle, was owing to the lateral position of the sun within it. M. Struve, however, rejects this explanation, and is of opinion that the most condensed stratum of the stars does not form a perfect plane, but rather a broken plane, (plan brisé,) or perhaps this stratum occurs in two planes inclined 10° to each other, and whose intersection is placed nearly in the plane of the celestial equator, the sun being at a small distance from this line of intersection towards the point 13 h. of the equator.§

Having already, in other articles, given an account of the great 40 feet telescope constructed by Dr. Herschel, and of the various discoveries which he made respecting the planets and satellites of our own system, we must bring to a close this brief notice of his sidereal labors. In the year 1816, when in the 79th year of his age, the prince regent presented him with the decoration of the Guelphic order of knighthood. In 1820, he was elected president of the Astronomical Society, and in their Transactions, in 1821, he published an interesting memoir On the places of 145 double stars. This paper was the last which he lived to publish. His health had begun to decline, and on the 24th August, 1822, he sank under the infirmities of age, having completed his 84th year. He was survived by his widow Lady Herschel, by his sister Miss Caroline Herschel, and by an only son, the present Sir John Herschel, whose labors and discoveries in sidereal astronomy we shall now proceed to lay before our readers.

After the death of his father, Sir John Herschel In 1786 Dr. Herschel, who had been honored had directed his attention principally to the science with the degree of Doctor of Laws from the Uni- of opties, but particularly to that branch of it which versity of Oxford, communicated to the Royal Soci- relates to the double refraction and polarization of ety a catalogue of 1000 new nebula and clusters of light. In this research, he obtained many new stars, which he had observed since 1783, with his and highly important results, which are recorded twenty-feet reflector; and this was followed, in in his Treatise on Light, published in the Encyclo1789, with another catalogue of a second thousand pædia Metropolitana, and certainly one of the most nebula. In these remarkable memoirs he regards valuable works on that subject which has ever been the round clusters and nebulæ, in which there is written. Astronomy, however, had a higher claim an apparent condensation towards a centre, as upon his genius; and having inherited telescopes clusters or nebulæ in the act of formation. He of great magnitude and power, and been initiated supposes that a central power resides in the brightest into the difficult art of constructing them, he was portion; that the clusters which have the most per-naturally led to quit the field of optical science, and fect spherical forms have been longest exposed to to cultivate the loftier domain of sidereal astronomy. the action of these forces; and that we may judge He had proposed to himself the arduous task of of the relative age and maturity of a sidereal sys-reëxamining the nebulæ and clusters of stars which tem from the disposition of its component parts; had been discovered by his father in his "sweeps while what he calls planetary nebula, where the of the heavens," and recorded in the three catacompression is more equal, may be regarded as very logues which, as we have already seen, he preaged, and approaching to a period of change or dis-sented to the Royal Society in the years 1786, 1787, solution.

These views, ingenious though they be, have

* See review of Kosmos No. vii, pp. 228–30.

+ In his memoirs of 1811 and 18:7, Mr. Herschel abandons altogether his postulate of the equal distribution of stars in space.

Etudes d'Astronomie Stellaire, par F. G. W. Struve. St. Petersbourg, 1847. p. 63.

§ Etudes d'Astronomie Stellaire, par F. G. W. Struve. St. Petersbourg, 1847. p. 82.

1802, and he began to execute it in the year 1925. In this reëxamination he spent eight years, and he has given the results of it in a catalogue published in the Philosophical Transactions for 1832. This * North British Review, No. vi., p. 477, and No. VIII., p. 490.

North British Review, No, H., pp. 183-189; No. VII., Art. viii passim, and No. xi., Art. viii. passim, Miss Caroline Herschel died at Hanover on the 9th of January, in the 98th year of her age.

catalogue contains 2306 nebulæ and clusters of quired than in England, was performed by himstars, of which 1781 are identical with those de- self with the requisite apparatus, which he had scribed by his father, and with those published by fortunately brought with him from England. Messier and Struve. The number of new nebulæ and clusters discovered by himself was 525. During this reexamination, he observed a great number of double stars, and took their places, to the amount of between three and four thousand, all of which are described in the second, third, fourth, sixth, and ninth volumes of the memoirs of the Astronomical Society of London.

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In the use of reflecting specula of considerable weight, it is of the utmost importance that the metal should be supported in its case so as not to suffer any change of figure from its own weight. Sir John found that a speculum was totally spoiled by allowing it to rest horizontally on three metallic points at its circumference. The image of every considerable star became triangular, throwing out These observations were made with a Newtonian long flaming caustics at the angles. Having on telescope of 20 feet focus, and 18 inches aperture, one occasion supported the speculum simply against and having acquired by practice a sufficient mas- a flat-board, at an elevation of about 45°, he found tery of the instrument," and "of the delicate that its performance was tolerably good; but on process of polishing the specula," he conceived the stretching a thin pack-thread vertically down the noble idea of attempting to complete the survey of middle of the board, so as to bring the weight of the whole surface of the heavens; and, with this the metal to rest upon this thread, the images of view, of "transporting into the other hemisphere stars were lengthened horizontally "to a preposthe same instrument which had been employed in terous extent, and all distinct vision utterly dethis, so as to give a unity to the results of both stroyed by the division of the mirror into two lobes, portions of the survey, and to render them com- each retaining something of its parabolic figure, parable with each other." separated by a vertical band in a state of distortion, The Cape of Good Hope was selected as the and of no figure at all!" The method which Sir most favorable locality for carrying on this survey; John found the best was the following:-Between and having fitted up the instruments and packed the mirror and the back of the case he interposed them carefully for the voyage, he left England, 6 or 8 folds of thick woollen baize, or blanketing, with his family, on the 13th November, 1833, and of uniform thickness and texture, stitched together landed at Capetown on the 16th January, 1834, at their edges. The metal, when laid flat on this having providentially escaped from an awful hurri-bed, was shaken so as to be concentric with the cane to which he would have been exposed had rim of the case, and two supports, composed of his voyage been delayed. The spot which Sir several strips of similar baize, were introduced so John selected was the grounds and mansion of a as to occupy about 30° each, and to leave an arc Dutch proprietor, the name of which was Feldhau- of about 40° unoccupied opposite the point which sen, a spot charmingly situated on the eastern was to be the lowermost in the tube. When the side of the last gentle slope at the base of the Ta- case is raised into an inclined position, and slightly ble Mountain." During the erection of the instru-shaken, the mirror takes its own free bearing on ments, Sir John resided at Welterfrieden, and so these supports, and preserves its figure. It is esquickly were his plans completed, that on the 22d of February, 1834, he was enabled to gratify his curiosity by viewing, with his 20 feet reflector, a Crucis, the interesting nebula about 7 Argus, and other remarkable objects; and on the evening of the 5th March, to begin a regular series of observations. The observatory thus completed was situated in south lat. 33° 58′ 56 55", and long. 22° 46' 9".11 east from Greenwich, and its altitude was 142 feet above the level of the sea in Table Bay.

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sential, however, to the successful application of this method that many thicknesses of the baize or blanket should be employed, "by which only the effect of flexure in the wooden back itself of the case can be eliminated." As the woollen fibres, however, lose their elasticity, the baize should be occasionally taken out, and beaten or shaken up.*

In conducting his observations with these fine instruments, Sir John Herschel observed several curious optical effects, arising from peculiar conditions of the atmosphere, incident to the climate of the Cape. In the hot season, from October to March, but particularly during the latter months of that season," the nights are for the most part superb" at a few miles distance from the mountains; but occasionally during the excessive heat and dryness of the sandy plains, the "optical tranquillity of the air" is greatly disturbed. In some cases the images of the stars are violently dilated into nebular balls or puffs of upwards of 15' in diameter. At the end of March, 1834, for example, when Saturn and y Virginis were both in the

After erecting his observatory, and determining its geographical position, the attention of Sir John Herschel was directed to the preparation of the telescopes with which his observations were to be made. He carried out with him three specula, one of which was made by his father, and used by him in his 20 feet sweeps and other observations; another was made by Sir John, under his father's inspection and instructions; and the other, of the very same metal as the last, was ground and figured by himself. They had all a clear diameter of 18 inches of polished surface, and were all equally reflective when freshly polished, and perfectly similar in their performance. The operation of repolishing, which was much more frequently re-nal, vol. ii., p. 207.

*When Sir John adopted this very simple plan, he was ignorant of the very ingenious method by which Lord Rosse affords an equable support to a large speculum, and which we have already described in this jour

star."

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field of the 20 feet reflector, "it could not have | In studying the polarization of the atmosphere, been told which was the planet and which the the writer of this article has had occasion freOn other occasions, the stars form "soft,quently to observe what appears to be the result quiet, round pellets of 3' or 4' diameter," resem- of the same cause. When the sky was of a fine bling planetary nebulæ, and quite unlike the spu- blue color, and free from clouds, and the degree rious discs which they present when not defined. of polarization, as indicated by the polarimeter,* In other cases, these pellets are seen to arise from very great, a sudden change frequently took place an infinitely rapid vibratory movement of the without any apparent, cause; sometimes near the central point in all possible directions," the lumi-horizon and not at considerable altitudes, and somenous discs presenting singular phenomena when times at considerable altitudes and not near the thrown out of focus, by pushing the eye-piece horizon. On some occasions the effect was limfurther in or pulling it further out than its princi-ited in its extent, and of a temporary kind. pal focus.* When it was not temporary, it showed itself in a In the cooler months, from May to October, diminution of the blue tint of the sky, which is and especially in June and July, the state of the invariably accompanied with a diminished polariair is habitually good, and after heavy rains have zation, and the whiteness of the sky often inceased for a day or two, the tranquillity of the creased till clouds were produced, terminating in image and the sharpness of vision, is such that rain. The cause of these phenomena was doubthardly any limit is set to magnifying power, but less a sudden secretion of aqueous vapor, somethat which arises from the aberration of the spec- times of local and of limited extent, and quickly ula. On occasions like these, optical phenomena reäbsorbed; and at other times general, and terof extraordinary splendor are produced by view- minating in a change of weather. When a cloud ing a bright star through diaphragms of card-board passed over a track of perfectly blue sky, without or zinc, pierced in regular patterns of circular occasioning any perceptible diminution of tint, the holes by machinery. These phenomena, arising polarization of the part of the sky over which it from the interferences of the intromitted rays, and passed was always diminished, owing, no doubt, produced less perfectly in a moderate state of the to its having left in its path a quantity of aqueous air, surprise and delight every person that sees vapor. them. A result of a more valuable kind is ob- The description of phenomena, and the tabutained when the aperture of the telescope has the lated observations contained in the interesting form of an equilateral triangle, the centre of which volume now before us, occupy seven chapters, coincides with the centre of the speculum. When extending over 450 closely printed pages, and are close double stars are viewed with the telescope, illustrated with seventeen beautifully executed having a diaphragm of this form, the discs of the plates, some of which are of a very great size. two stars, which are exact circles, are reduced to The valuable contents of these different chapters about a third of their size, and have a clearness would doubtless have appeared in a series of unand perfection almost incredible. These discs, connected memoirs in the transactions of the however, are accompanied with six luminous radi- Royal or Astronomical Societies, and with illusations, running from them at angles of 60°, form-trations very inferior, both in number and quality, ing perfectly straight, delicate, brilliant lines, like had it not been for the munificence of his grace brightly illuminated threads, running far out be- the late Duke of Northumberland, who destined yond the field of view, and, what is singular, a large sum for their publication as a single and capable of being followed like real appendages to separate work. This very amiable and publicthe star long after the star itself has left the field. spirited nobleman, to whom the observatory of Another optical phenomenon, arising from a Cambridge owes the gift of the splendid Northpeculiar condition of the atmosphere, is described umberland achromatic telescope, through which by Sir John Herschel as a "nebulous haze." the new planet Neptune was first seen, did not The effect of it is to encircle every star, of the live to witness the final fulfilment of his noble and 9th magnitude and upwards, with a faint sphere generous design; but the present duke, the worof light of an extent proportioned to the bright- thy heir of the titles and the fortune of that disness of the star. This phenomenon presents tinguished nobleman, carried out, in the fullest itself very suddenly in a perfectly clear sky, free manner, the liberal intentions of his lamented from the slightest suspicion of cloud, and disap-brother, and thus added another claim to those pears as suddenly, lasting sometimes only for one which, as Lord Prudhoe, he had already earned, or two minutes. Sir John Herschel states that upon the gratitude and esteem of the literary and similar nebular affections occur in our English cli-scientific world.

mate, but with much less frequency and sudden- The following are the subjects which are treated ness in their appearance and disappearance. He in the volume under our notice :

at first suspected that the phenomenon arose from

Chap. I. On the nebula and clusters of stars

dew upon the eye-piece, but repeated examination in the southern hemisphere. satisfied him that its origin was really atmospheric.

* Sir John supposes that these phenomena may be produced by ascending and descending currents of hot and cold air rotating spirally.

* For an account of the polarization of the atmosphere, the reader is referred to Johnston and Berghaus' Physical Atlas, part vii., and London and Edinburgh Philosophical Magazine, December, 1847. Vol. xxxi., pp. 441-455.

II. On the double stars of the southern hem-time ruddy or orange yellow,) forming a fine conisphere. trast with the white light of the exterior portion. III. Of astronomy, or the numerical expression There is a beautiful double star on the south preceding edge of the last portion, but it is probably unconnected with the cluster.

of the apparent magnitude of stars.

IV. Of the distribution of stars, and of the constitution of the galaxy, or Milky Way, in the southern hemisphere.

V. Observations of Halley's Comet, with remarks on its physical condition, and that of comets in general.

VI. Observations on the Satellites of Saturn.
VII. Observations on the Solar spots.

In the first chapter, on nebulæ and clusters of stars, occupying 164 pages, our author proceeds, after some introductory and explanatory remarks, to give detailed descriptions and monographs of some of the more remarkable of the nebulæ. As some of these nebulæ are visible in Europe, and are all objects of singular interest, we shall lay before our readers a very brief notice of the most important of them.

Right Ascension. North Po.ar Distance. 18h 11'

No. of stars laid down in the drawing.

No.

1.

106° 15'

44

6

186 110

12 43 36 149 25 41 7 0 16 24 163 1 58

No. 1. This remarkable nebula, which is a nebular line, with the figure of a horse-shoe at each end of it, has been observed and drawn by Mr. Mason, an American astronomer, and Mr. Lamont, a native of Scotland, who has the charge of the observatory at Munich. Mr. Mason, whose premature death is deeply to be regretted, used a reflecting telescope of 12 inches aperture, and 14 feet focal length, constructed by himself. The fainter horse-shoe was seen neither by Mr. Mason nor Mr. Lamont.

Under the favorable circumstances in which he was placed, our author eagerly availed himself of the opportunity of studying the grand nebula in the sword-handle of Orion, which passed the meridian of the Cape at an altitude of 60°. He had himself delineated this remarkable nebula in 1824: Four representations of it, differing essentially from his, had been subsequently published; and it therefore became an object of the deepest interest to discover the causes of these discrepancies, and to ascertain whether or not a change had taken place either in the form or luminosity of the whole nebula, or of any of its parts. Dr. Lamont of Munich, had, in 1837, published "rather a coarsely executed figure" of this nebula, but Sir John Herschel acknowledges that it " contains some valuable particulars respecting the apparent breaking up of the nebula into patches and knots," which had been very unsatisfactorily expressed in his figure of 1824, but "in which his observations of 1834 and 1837, fully confirm Dr. Lamont's remarks." The other drawings, by Sig. Devico, and Sig. Rondoni, published in 1839, 1840 and 1841, are too inaccurate to furnish any materials for speculation.

The splendid drawing of this nebula, which occupies a foot square, and forms the eighth plate of the present work, is one of the noblest specimens of astronomical research which is to be found in the history of the science. We view it at first with mute admiration of the skill and patience of the observer, and even forget for a while the mysterious assemblage of suns and of systems which it sets before us. No fewer than 150 stars are accurately laid down in this remarkable map, and our failing vision can scarcely descry the faint luminosity with which it shades away into the dark

No. 2. This nebula has also been figured by Mr. Mason, and in this as well as in No. 1, his representation differs from that of Sir John Her-sky that encloses it. Neither in its general outschel.

No. 4 is, in the author's opinion, one of the most singular and extraordinary objects which the heavens present. It is situated in the greater nubecula of the Magellanic clouds.

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line, nor in that of its individual portions, has it the least resemblance to any form natural or artificial. The luminous portions have no relation either in shape or intensity to the stars which bespangle it, and the stars themselves, whether we consider their magnitude or their distances, seem

No. 6. This cluster of stars, improperly set down as nebular by Lacaille, is, according to our to have no bond of union, and no symmetry of author, an extremely brilliant and beautiful ob-place. Knowing, as we now do, that Lord Rosse's ject, when viewed through an instrument of suffi- telescope has resolved the nebulous portion into cient aperture to show distinctly the very different stars, we can no longer satisfy ourselves with the colors of its constituent stars, which give it the speculation that the nebula is a collection of mineffect of a superb piece of fancy jewelry." Three utely subdivided matter, accidentally irregular in of the stars are greenish white, two green, one its outline and density, which may some time or blue green, one red, and another ruddy. other be combined into stars and planets, but we No. 7, (47 Toucani,) is a most magnificent view it as a mighty galaxy of systems already globular cluster. The stars are immensely numer-formed, of suns radiant with light and heat, of ous and compressed. It is compared to a blaze worlds in harmonious revolution, teeming with orof light at the centre, the stars seeming to run ganic life, and rich with the bounties of their beneftogether. Sir John Herschel has observed the icent Creator. But even with these views the extraordinary fact that the inner or compressed mind does not rest satisfied. It seeks to know part of the cluster is rose-colored, (at another how these systems are combined in the irregular