CHAPTER XVII.. _nebulæ and Clusters of Stars._

NEBULÆ AND CLUSTERS OF STARS.

Distinction.—Large number of Nebulæ and Clusters visible.—Varieties of form and grouping.—Distribution.—Early Observations.—Variable Nebulæ.—Nebulous Stars.—The Magellanic Clouds.—Double Nebulæ.—Real dimensions of Nebulæ and Clusters.—Round Nebulæ and Clusters.—Description of Objects.—Further Observations required.—Lists of selected Objects.

Distinction.—These objects, though classed together in catalogues, offer some great distinctions which the observer will not be long in recognizing. It was thought at one period that all nebulæ were resolvable into stars, and that their nebulous aspect was merely due to the confused light of remote star-clusters. But modern telescopes, backed up by the unequivocal testimony of the spectroscope, have shown that purely nebulous matter really exists in space. The largest instruments cannot resolve it into stars, and it yields a gaseous spectrum. The conjecture has been thrown out that it may be considered as the unformed material of which suns and planets are made.

Large Number visible.—D’Arrest once said that nebulæ are so numerous as to be infinite, and his opinion is supported by the rapid increase in the number known. Let us make a comparison. Messier inserted in the Connaissances des Temps for 1783 and 1784 (published in 1781) a catalogue containing 103 nebulæ and star-clusters. Of these 68 were new. In 1888 a new edition of Sir J. Herschel’s catalogue of 1864 (revised and extended by Dreyer) was printed by the Royal Astronomical Society, and this includes 7840 objects! The labours of the Herschels, of Lord Rosse, D’Arrest, Marth, Tempel, Stephan, and Swift have vastly augmented our knowledge in this branch since the time of Messier.

Varieties of Form and Grouping.—A telescope reveals all grades of condensation in stellar groups. Some consist of rather bright, scattered stars, and are easily resolved. Others contain more stars, but they are smaller, and greater power is required to show them. Others again are condensed into globular clusters needing high powers and good instruments to disconnect the mass of stars composing them. Some are faint, and the stars so minute that they are only to be distinguished from nebulæ in the finest telescopes. As to the nebulæ properly so called, they exist in all forms. They may be either round, elliptical, or in the form of a streak. Some are highly condensed in their centres, others present well-defined circular disks like planets, and a small proportion are in the form of rings. Many peculiarities of detail have been remarked, and a curious and complicated spiral structure has been discovered in certain prominent nebulæ. One of these has been termed the “Whirlpool” Nebula from its singular convolution of form. Other objects have received distinctive appellations agreeably to their appearance. Thus, there is the “Dumb-bell” Nebula, the “Crab” Nebula, the “Horseshoe” Nebula, &c. Lord Rosse’s 6-foot reflector is in a large degree responsible for the particular knowledge we possess of many of these objects. The large mirror commands a grasp of light which renders it very effective on forms of this character. An instrument of small diameter is quite inadequate to deal with them. They can be seen, it is true, and the general shape recognized in the most conspicuous examples, but their details of structure are reserved for the greater capacity of large apertures.

Distribution.—With regard to distribution these objects exhibit the utmost irregularity, for in certain regions of the heavens they are found to be very plentiful, while in others they are singularly rare. Thus, in Virgo, Coma Berenices, Leo, and Ursa Major large numbers of nebulæ abound, while in Hercules, Draco, Cepheus, Perseus, Taurus, Auriga, &c., very few are encountered. Taking the 7840 objects in the New General Catalogue of 1888 it will be found that their distribution in hours of Right Ascension is as follows:—

R.A. Nebulæ. 0 H. 387 I 428 II 398 III 300 IV 276 V 375 VI 171 VII 196 VIII 230 IX 362 X 404 XI 585 XII 858 XIII 504 XIV 375 XV 212 XVI 230 XVII 259 XVIII 203 XIX 117 XX 153 XXI 188 XXII 275 XXIII 354

The maximum is therefore reached at XII hours, while the minimum is shown at XIX h. There is a secondary max. at I h., and a secondary min. at VI h.

Early Observations.—The nebula in Andromeda appears to have been the one first discovered, for the distinguished Persian astronomer Al-Sûfi (who died in 986 A.D.) was undoubtedly acquainted with it. The nebula is figured upon a Dutch map of the stars nearly 400 years old. In 1612 Simon Marius redetected this object, and appropriately likened its appearance to that of a “candle shining through a piece of horn.” In 1618 the nebula in Orion was certainly known, for Cysatus of Lucerne compared it with the head of the fine comet visible in December of that year. Huygens alighted upon the same object in 1656, and appears to have been unconscious of its prior discovery. Only six “nebulæ or lucid spots” were known in 1716, and enumerated by Halley in the ‘Phil. Trans.’ vol. xxix. These included those of Andromeda and Orion. A third was situated in the space between the bow and head of Sagittarius. This is M. 22, and consists of a bright globular cluster of Stars. The fourth was the fine star-group involving ω Centauri, which Halley himself found in 1677. The fifth was another fine group in the right foot of Antinous. This is M. 11, and was discovered by Kirch in 1681. The sixth was the magnificent globular cluster (M. 13) in Hercules, discovered by Halley in 1714.

In 1735 the Rev. W. Derham published a list of 16 of these objects, and in 1761 Lacaille summarized 42 nebulæ and star-clusters which he had observed in the southern sky. This was followed by Messier’s tables of 45 nebulæ &c. in 1771, and of 103 in 1781. But these contributions, important though they severally were, sunk into insignificance beside the splendid results obtained by Sir W. Herschel, who during his prolonged and systematic sweeps of the heavens picked up no less than 2500 new nebulæ and clusters which he formed into three catalogues printed in the ‘Phil. Trans.’ as follows:—1786, 1000 objects, 1789, 1000 ditto, 1802, 500 ditto.

Variable Nebulæ.—It is in the highest degree probable that changes occur in the physical appearances of certain nebulæ, though the opinion is not perhaps supported by a sufficient number of instances. Until Sir W. Herschel began his review of the heavens very few nebulæ were known, and the information possessed about them was very incomplete. The early records, obtained with small and inferior telescopes, scarcely admit of comparison with recent observations, for in matters of detail little agreement will be found; and this proceeds certainly not so much from real changes in the objects as from differences due to the variety of instruments employed, to atmospheric vagaries, and to “personal equation.” Bullialdus and Kirch in 1667 and 1676 and Le Gentil in 1759 supposed that remarkable changes were operating in the great elliptical nebula of Andromeda. But G. P. Bond fully investigated the evidence, and concluded that the variability of the object was by no means proved. Some observers have represented the nucleus as stellar, while others have drawn it as a gradual condensation, and Dr. Copeland has shown that different magnifying powers alter the aspect of the nucleus, “the lower powers making it more star-like, the higher ones more soft-looking and extensive.”

Mairan and others entertained the view that the large irregular nebula in Orion was subject to change. This object received much attention from Sir W. Herschel, and he concluded that it underwent great alteration between 1774 and 1811. D’Arrest, from his own researches and a discussion of other results, expressed himself in 1872 that “the observed changes in this vast mass of gas seem exclusively to turn out to be temporary fluctuations of brightness.” Prof. Holden has arrived at a similar conclusion, and says:—“The figure of the nebula has remained the same from 1758 till now (if we except a change in its apex about 1770, which seems quite possible); but in the brightness of its parts undoubted variations have taken place, and such changes are still going on” (‘Monograph of the Nebula in Orion,’ p. 225).

Hind discovered a faint nebula, with a diameter of about 1′, on Oct. 11, 1852. It was situated in Taurus, the position being R.A. 4^h 15^m 33^s, Dec. +19° 15′·6 (for 1890), or about 2° W. of the star ε Tauri (mag. 3·7). D’Arrest, on Oct. 3, 1861, searched for this object, but found it had quite disappeared! A small round nebula was seen in 1868, about 4′ preceding Hind’s, but this resisted some later attempts at observation. In Oct. 1890, Burnham and Barnard, with the 36-inch refractor of the Lick Observatory, saw two nebulæ here, one a very small, condensed nebula, with a stellar nucleus, and the other an exceedingly faint nebulosity about 45″ in diameter (see ‘Monthly Notices,’ vol. li. pp. 94, 95).

The nebula surrounding the star ζ Argûs has been suspected of variation, particularly by Abbott, of Hobart Town, Tasmania. Vols. xxv., xxx., and xxxi. of the ‘Monthly Notices’ contain many references to, and figures of, this interesting object. But the alleged changes have not been substantiated, and there seems no reason to doubt that they were purely imaginary.

The trifid nebula in Sagittarius (M. 20) is supposed by Prof. Holden to have altered its position with reference to a triple star now situated in the S. following part of the nebula. Sir J. Herschel, more than half a century ago, had described this star as placed in the middle of the vacuity by which the nebula is divided. Dreyer, however, points out that the drawings of this object differ in many details, and that, though changes of brightness may have taken place, it is difficult to understand that the nebula should move so as to envelop the star in about 1835, “after which no sensible change occurred again, so far as published observations go.”

The nebula (M. 17) just N. of the bow of Sagittarius was also inferred by Holden to have shifted its place relatively to the small stars figured by Lassell in this object; but Dreyer adduces facts which controvert this assumption. (See ‘Monthly Notices,’ vol. xlvii. pp. 412-420, where much valuable information will be found as to supposed variable nebulæ.)

On Oct. 19, 1859, Tempel discovered a faint, large nebulosity attached to the star Merope, one of the Pleiades, and at first mistook it for a diffused comet. Its position is R.A. 3^h 39^m·6, Dec. +23° 26′ (1890). An impression soon gained ground that this object was variable; for while Schmidt, Chacornac, Peters, and others saw it with small instruments, it could not be discerned by D’Arrest and Schjellerup with the large refractor at Copenhagen. Swift saw the nebula easily in 1874 with a 4½-inch refractor, and has observed it with the aperture contracted to 2 inches. Backhouse re-observed it in 1882 with a 4-1/4-inch refractor. Yet in March 1881 Hough and Burnham sent a paper to the Royal Astronomical Society with an endeavour to prove that the nebula did not exist! They had frequently searched for it during the preceding winter, but not a vestige of the object could be seen in the 18½-inch refractor at Chicago, and they regarded the supposed nebula as due to the glow proceeding from Merope and neighbouring stars. But photography has entirely refuted this negative evidence, and has shown, not only Tempel’s nebula, but others involving the stars Maia, Alcyone, and Electra belonging to this cluster. As to the alleged variations in the Merope nebula, there is every reason to suppose these were not real.

Proper motion has been suggested in regard to a very small, faint nebula (N.G.C. 3236) a few degrees following α Leonis. But Dreyer has disproved this by showing that there was no proper motion between 1865 and 1887, whence “it may be safely inferred that there has been none since 1830, unless we are to believe, in this and similar cases, that nebulæ in the good old days moved about as they liked, but have been on their good behaviour since 1861.”

Nebulous Stars.—This name was applied by Hipparchus and other ancient observers to the clusters of stars which, to the naked eye, appear as patches of nebulous light. Sir W. Herschel, in 1791, showed this designation to be incorrect, and used it in connection with stars actually involved in nebulosity. In sweeping the heavens he met with several instances of this kind. Thus, 3° E.S.E. of ζ Persei he found a star of the 9th mag. surrounded by a nebula 3′ in diameter. He picked up another close to the star 63 Geminorum. This is a remarkable object—a star of the 9th mag. surrounded by two dark and two bright rings. On Feb. 3, 1864, Lord Rosse’s telescope showed an opening in the outer bright ring, and the latter seemed connected with the inner bright ring; so that the object presented the aspect of a spiral nebula with a star in the centre. The diameter of the whole nebulosity is 45″. Key observed this object with an 18-inch reflector in 1868, and described it as symmetrical—a central star, with intervening dark and bright rings. He found a power of 510 the best, for, “like the annular nebula in Lyra, it bears magnifying wonderfully well.” Since Herschel’s time many nebulous stars have been discovered. There is one of about 6th mag. in R.A. 8^h 6^m·1, Dec.-12° 36′. The nebulosity round the star fades away gradually, and its extreme diameter is 157″. There is a 7th mag. star at R.A. 21^h 0^m 14^s, Dec. +67° 44′ involved in a very large, faint nebulosity. This is a striking object, and I have frequently picked it up while comet-seeking. The star has such a foggy, veiled appearance that on first remarking it the observer thinks his lenses are dewed, but on viewing neighbouring stars he sees them sharp and clear on the dark sky, and the contrast is very pronounced. The nebulous star is much isolated, though in a part of the sky where small stars abound. This is one of Herschel’s discoveries and No. 7023 of the N. G. C.; Dreyer says he has seen the nebulosity particularly distinct north and south of the star. In some cases a double star is involved in nebulosity, and there are instances in which two double stars are placed within an elliptical nebula.

The Magellanic Clouds.—These are marked as Nubecula Major and Nubecula Minor on celestial globes and charts. They form two extensive aggregations of nebulæ and star-clusters, and are readily visible to the naked eye in or near Hydrus, and not far from the south pole of the heavens. They may be likened to detached patches of the Milky Way. Sir J. Herschel says the Nubecula Major is situated between the meridians of 4^h 40^m and 6^h and the parallels of 66° and 72° of S. declination, and extends over a space of some 42 square degrees. The Nubecula Minor lies between 0^h 28^m and 1^h 15^m and 72° and 75° of S. declination, and spreads over about 10 square degrees. The composition of these objects is very complex and diversified, and affords very rich ground for exploration with a large telescope. Nebulæ exist in profusion and in every variety, and are intermingled with star-clusters varying in condensation from the compact globular form to groups more loosely scattered, and such as we often find in the Milky Way. Nearly three hundred nebulæ and clusters are included in the major “cloud,” while more than fifty others closely outlie its borders. In the minor about forty such objects have been discovered. It is very strange to find them collected together in this manner; for in other regions of the firmament they are usually found separated, and certain classes appear to have their own special zones or localities of distribution. Sir J. Herschel pointed out that “globular clusters (except in one region of small extent) and nebulæ of regular elliptic forms are comparatively rare in the Milky Way, and are found congregated in the greatest abundance in a part of the heavens most remote possible from that circle, whereas in the Nubeculæ they are indiscriminately mixed with the general starry ground and with irregular though small nebulæ.”

Double Nebulæ.—Instances are not wanting of conspicuous double nebulæ. M. 51 and 76, near ζ Ursæ and θ Andromedæ, may be classed in this category. There is a very interesting, though a smaller object just W. of α and β Geminorum, or in R.A. 7^h 18^m·6, Dec. +29° 43′. Two bright, round nebulæ are separated by an interval of 28″. These double nebulæ are usually round, and are sometimes resolvable into stars. Whether they are physical or mere optical pairs has yet to be ascertained. So many examples exist that it seems highly probable they have a real connection, though no motion has yet been certainly detected to prove they are binary systems. Such motion may, however, be very slow, and require observations extending over a much longer interval before it is revealed.

Real Dimensions of Nebulæ and Clusters.—It may be readily imagined that these objects are of immense size; for though placed at distances of the utmost remoteness, they spread over perceptible and comparatively large areas. Gore remarks that, on the assumption that the globular cluster in Hercules (M. 13) is 5′ in diameter, and its parallax one tenth of a second, its real diameter must be 3000 times the Sun’s mean distance from the Earth, or nearly 280 billions of miles! He further points out that, though this group contains as many as 14,000 stars, according to Sir W. Herschel, yet each component may be separated many millions of miles from the others, owing to the vast dimensions of the group. Details like these are of course only approximate, as the distance of a nebula or star-cluster has not yet been definitely ascertained. The great nebulæ of Orion and Andromeda must extend over prodigious regions in distance-space; but to quote figures seems useless, in consequence of our inability to form just conceptions of such immensity.

Round Nebulæ and Clusters.—Resolvable nebulæ and clusters are frequently circular in outline. The central condensation is an indication of their globular form, though not always so, for many of these objects become suddenly much brighter in the middle, and show an apparently stellar nucleus. The material or stars forming the object cannot therefore be equally distributed. Where it suddenly brightens there is a great condensation, and in some cases several of these are evident in the form of bright rings, intensifying as the nucleus is approached. This irregular aggregation denotes the operation of “a force of condensation directed from all parts towards the centre of such systems.” In regard to planetary nebulæ, they cannot be globular or they would exhibit a brightness increasing from the margin to the centre. Their even luminosity throughout affords the evidence of a special structure. Sir J. Herschel thought the planetary nebula (M. 97) near β Ursæ Majoris must either be in the form of a hollow globe or a flat circular disk lying perpendicular to the line of vision.

Description of Nebulæ and Clusters of Stars.—The latter objects are included in this chapter for several reasons. In a small telescope nearly all such clusters exhibit the aspect of nebulæ, and they have been catalogued with them, though, as already explained, some great distinctions are to be drawn. To the naked eye the cluster Præsepe, in Cancer, is usually visible as a patch of nebulosity, though on a very clear, dark night stars may be glimpsed sparkling about the spot, and a very small glass will suffice to show it as a nest of stars. This object, and some others of a more difficult character (their component stars being smaller and more compressed), are tabulated (I.) at the end of this chapter. A summary (II.) of globular clusters is also given, together with a list (III.) of nebulæ, a few of which are resolvable into stars. It must be understood that these selections, though comprising many notable objects, are by no means exhaustive, the intention being merely to indicate some typical examples of fine nebulæ and clusters and of peculiarities of form or appearance, such as planetary, annular, elliptical, and centrally condensed nebulæ and loose, compressed, and globular clusters. Some of these objects deserve individual references, as they present interesting details to the telescopic observer and come within the reach of moderate appliances.

Great Nebula in Andromeda (M. 31). This object has often been mistaken for a comet, for it is readily perceptible to the eye on a moonless night. It is very large—4° by 2½°, according to Bond, with a 15-inch refractor. He discovered a pair of dark streaks in the brightest region of the nebula, and these may be well seen in a 10-inch reflector. It is really triple; for about 25′ S. of the nucleus there is a very bright, round, resolvable nebula, discovered by Le Gentil, and a third, observed by Caroline Herschel, lies rather further to the N.W. Photographs by Roberts show dark rings dividing the bright interior parts of the nebula from the outer, and imparting to it a decided spiral tendency. This nebula has hitherto resisted attempts to resolve it into stars, though many hundreds have been seen in the foreground. But its spectrum is continuous, so that its stellar character is to be inferred.

Great Nebula in Orion (M. 42). Visible to the naked eye just below a line connecting β and ζ Orionis, and involving θ Orionis. It exhibits an extremely complicated structure, and many of its irregular branches and condensations may be discerned in small instruments. Sir W. Herschel failed to resolve this object into stars with his 4-foot reflector; but Lord Rosse, in 1844, thought he had effected it with his 6-foot mirror, though the conclusion was premature. The spectroscopic researches of Huggins have shown this nebula to be composed of incandescent gases, so that the stars telescopically observed in it are probably in the foreground and entirely disconnected from the nebulous mass. Effective photographs have been taken of it by Draper, Common, and Roberts. It certainly forms one of the grandest objects in the heavens.

The Planetary Nebula (M. 97). Discovered by Mechain in 1781. In small telescopes it looks like a rather faint, round mass of nebulosity, somewhat brighter in the middle than at the edges. In Lord Rosse’s telescope it shows many details, including a spiral arrangement and two dark spots in the middle inclosing bright, eye-like condensations. The margin is fringed with protuberances, and from its peculiar aspect this object has been called the “Owl” Nebula. Diameter between 155″ and 160″. It may readily be picked up 2-1/4° S.E. of β Ursæ Majoris. It yields a gaseous spectrum.

In Draco at R.A. 17^h 58^m 36^s, Dec. +66° 38′ there is a pretty small, but exceedingly bright planetary nebula. With a low power it looks like a star out of focus, but a high power expands it into a well-defined planetary disk. As observed in Lord Rosse’s 3-ft. reflector on Sept. 17, 1873, this nebula exhibited “a round, well-defined disk of a full blue colour, light very equable, diameter 22″·4, surrounded by an extremely faint nebulosity.” This is an excellent object of its class.

Spiral Nebula (M. 51). Discovered by Messier on Oct. 13, 1773. It is situated in Canes Venatici, and 4° S.W. from ζ Ursæ Majoris. An ordinary instrument will reveal it as a double nebula, and the two parts will be seen to differ greatly in size. Messier gave the distance separating them as 4′ 35″. Sir J. Herschel drew this object as a bright, centrally condensed nebula, surrounded by a dark space and then by a luminous ring divided through nearly one half of its circumference. Closely outlying this he placed a bright round nebula. Lord Rosse’s 6-foot showed something very different. In April 1845 its spiral character was discovered; coils of nebulosity were observed tending in a spiral form towards the centre, and the outlying nebula was seen to be connected with it. Some striking drawings have been published of this object. Those by Sir J. Herschel and Lord Rosse differ essentially, and would scarcely be supposed to represent the same nebula; but when we reflect that the instruments used were respectively of 18 inches and 72 inches aperture, the cause of the disparity becomes evident.

Another fine example of a spiral nebula is M. 99, in the northern wing of Virgo, and 8° E. of β Leonis. This object was discovered by Mechain; its spiral form of structure was detected by Lord Rosse in 1848. Diameter 2½′ Like M. 51 it gives a continuous spectrum and is resolvable into stars.

1. Nebula with bright centre.

2. Planetary Nebula.

3. Ring-nebula in Lyra.

4. Star-cluster in Hercules.]

The Crab Nebula in Taurus (M. 1). Discovered by Bevis in 1731, and situated 1° N.E. of ζ Tauri. Its diameter is 5½′ by 3½′. An early drawing with Lord Rosse’s telescope shows it with numerous radiations; whence it was termed the Crab Nebula, from the supposed resemblance: but later observations have given it quite another form. In 1877 there was no trace of the nebulous arms: it appeared as a well-defined, oval nebula with some irregularities of structure. This object is very plain in small telescopes, and may be readily picked up from its proximity to ζ Tauri; but in such instruments it is void of detail, and merely presents a pale, oval nebulosity. It has not been clearly resolved, though it has a mottled appearance, indicating a stellar composition, in large apertures.

The Dumb-bell Nebula (M. 27). Discovered by Messier in 1779, and situated in Vulpecula—a region very rich in small stars. Diameter about 7′ or 8′. Its general form resembles a dumb-bell or hour-glass; hence its name. Struve, Lord Rosse, and others have seen many stars in the nebulous mass, but the latter is not resolvable. I have seen seven stars in the nebula with a 10-inch reflector. Its peculiar shape is perceptible in a small instrument. This object frequently serves to illustrate books on Astronomy; but the drawings by Sir J. Herschel, Lord Rosse, and others are curiously discordant, and show how greatly differences in telescopic power may affect the observed appearance of an object.

The Ring-Nebula in Lyra (M. 57). Discovered by Messier between the stars β and γ Lyræ. Diameter 80″ by 60″. This object is bright, though rather small, and it will stand high powers. The dark centre may possibly be glimpsed in a 3-inch refractor; I have seen it readily in a 4-1/4-inch. It was at one period thought to be resolvable, but the spectroscope has negatived the idea, and shown it probably consists of nitrogen gas. A small star near the centre was frequently seen in Lord Rosse’s telescope; but the 36-inch refractor at Mount Hamilton reveals twelve stars projected on or within the ring, and several others have been suspected. There is a faint star exterior to the ring, and following it; this is visible in small telescopes. The space within the ring is not quite dark, and the structure of the nebula is somewhat complicated as seen in large instruments. Another fine instance of an annular nebula may be found 3° preceding the 4th mag. star 41 Cygni, but it is not so large or conspicuous as that in Lyra. Its diameter is 47″ by 41″. Several stars were seen sparkling in it by Lord Rosse, who found the centre was filled with faint light and the N. side of the ring broadest and brightest.

Elliptical nebulæ are well represented by the pair (M. 81 and 82) about 2° E. of δ (22) Ursæ Majoris. They are separated by about 38′ of declination, so that they may be observed in the same field of a low-power eyepiece. The preceding one is very bright and large (8′ by 2′). The following one is a ray or streak of nebulosity (7′ by 3/4′). On May 21, 1871, the great Rosse telescope showed the latter as a most extraordinary object, at least 10′ in length and crossed by several dark bands. Roberts photographed these nebulæ on March 31, 1889. “The negative shows that the nucleus [of M. 81], which has not a well-defined boundary, is surrounded by rings of nebulous or meteoric matter, and that the outermost rings are discontinuous in the N.p. and S.f. directions.” M. 82 is “probably a nebula seen edgeways, with several nuclei of a nebulous character involved, and the rifts and attenuated places in it are the divisions of the rings that would be visible as such if we could photograph the nebula from the direction perpendicular to its plane” (‘Monthly Notices,’ vol. xlix. p. 363). This fine pair may be easily picked up in a small instrument. Another grand object of this class (discovered by Caroline Herschel in 1783) lies in R.A. 0^h 42^m·2, Dec.-25° 54′, between the stars β Ceti and α Sculptoris.

Globular clusters furnish us with many examples of easily resolved and richly condensed balls of stars. M. 3 (discovered by Messier), M. 5 (discovered by G. Kirch), and M. 13 (discovered by Halley) may be selected as amongst the finest of these objects in the northern hemisphere. They are severally visible to the naked eye, and may be found in a telescope directed as follows:—M. 3, between Arcturus and Cor. Caroli, and nearer the former; M. 5, 7° S.W. of α Serpentis and close to the double star 5 Serpentis; M. 13, one third the distance from ζ to ζ Herculis. They are brilliant objects from 5′ to 7′ diameter. With power 60 on my 10-inch reflector they are spangled with stars, though not fully resolved. Smyth described M. 3 as consisting of about 1000 small stars, blazing splendidly towards the centre. Webb hardly resolved it with a 3-7/10-inch refractor. Another fine object of this class (M. 80) will be encountered midway between α and β Scorpii. Sir W. Herschel described it as the richest and most compact group of stars in the sky, and it is noteworthy from the fact that a new star burst forth near its centre in 1860. There is a magnificent cluster, involving ω Centauri, which Sir J. Herschel considered as “beyond all comparison the richest and largest object of the kind in the heavens.” It is visible to the naked eye as a 4th mag. star, but residents in northern latitudes are precluded from a view of it. Pegasus also supplies us with some fine clusters; Maraldi picked up two in 1746 (M. 2 and 15), and these will respectively be found 5° N. of β and 4° W.N.W. of ε Pegasi. They are to be classed amongst the grandest objects of their kind.

In Cygnus, at R.A. 20^h 41^m 7^s, Dec. +30° 19′, near κ and especially in the region immediately north-east, there exist irregular and extensive streams of faint nebulosity which may be said to form a telescopic milky way, Nebulæ and stars are curiously grouped together, forming a remarkable arrangement which will well repay study. To see these objects satisfactorily, a moonless night, free from haze or fog, should be chosen, and the power should be moderately low, or some of the more feeble nebulous films will be lost. The observer may spend some agreeable hours in sweeping over this region, which is one of the best in a wonderfully rich constellation.

Further Observations.—The fact that Swift has discovered many hundreds of nebulæ during the last few years affords indubitable proof that considerable numbers of these objects still await detection. No doubt they are generally small and faint, but it is necessary they should be observed and catalogued, so that our knowledge in this department may be rendered as complete as possible. New nebulæ are sometimes mistaken for expected comets, and occasionally give rise to misconceptions which would be altogether avoided were our data more exhaustive.

Those who sweep for nebulæ must have the means of determining positions, and a small telescope will be inadequate to the work involved. A reflector of at least 10 inches, or refractor of 8 inches, will be required; and a still larger instrument is desirable, for to cope successfully with objects of this faint character needs considerable grasp of light. The power employed should be moderate; it must be high enough to reveal a very small nebula, but not so high as to obliterate a large, diffused, and faint nebula. In forming his first catalogue of 1000 nebulæ, Sir W. Herschel used a Newtonian reflector of 18·7 inches aperture, power 157, field 15′ 14″; Swift’s recent discoveries were effected with a 16-inch refractor and a periscopic positive eyepiece, power 132, field 33′. With a low power a very extensive field will be obtained, and a large part of the sky may soon be examined, but it will be done ineffectively. It is better to use a moderately high power, and thoroughly sweep a small region. The work is somewhat different to comet-seeking; it must proceed more slowly and requires greater caution, for every field has to be attentively and steadily scanned. If the telescope is kept in motion, a faint nebula will pass unseen. Some of these objects are so feeble that they are only to be glimpsed by averted vision. When the eye is directed, say, to the E. side, a faint momentary glow comes from the W. side of the field; but the observer discerns nothing on looking directly for the object. On again diverting his gaze he receives another impression of faint nebulosity from the same point as before, and becomes conscious of its reality. Frequently, while comet-seeking, I meet with a small indefinite object, the character of which cannot be determined by direct scrutiny. On withdrawing the eye to another part of the field, however, the mystery is solved. If the object is a nebula, it flashes very distinctly on the retina; but if a small cluster, the individual stars are seen sparkling in it. These indirect views are usually so effective that the trouble of applying higher powers is dispensed with.

The glow from a faint nebula or comet often apparently fluctuates in a remarkable manner. Light-pulsations affect it, causing the nebulosity to be intermittently visible. It flashes out and enlarges, then becomes excessively feeble and indeterminate. The changes are not real, but due to the faint and delicate nature of the object, which is only fugitively glimpsed and presents itself differently with the slightest change in the manner of viewing it. Burnham has said there is no such thing as glimpsing an object; but he is wrong. It is the intermediate step between steady visibility and absolute invisibility.

The work of sweeping for nebulæ is much delayed by the comparisons necessary for the identification of objects. The path may be smoothed by marking the known nebulæ on a good chart, like Argelander’s. The observer may then see, by reference, whether the objects he encounters have been picked up before. The labour of projecting all the nebulæ contained in the New General Catalogue would of course be considerable, and the observer will probably find it expedient to select certain regions for examination, and map such nebulæ as are included within their borders.

The discovery of new nebulæ offers an inviting field to amateurs. Vast numbers of these objects have escaped previous observation, for though the sky has been swept again and again, its stores have not been nearly exhausted. Mr. Barnard recently stated that with the powers of the great 36-inch refractor the number of known nebulæ (more than 8000) might readily be doubled! As an example of their plentiful distribution in certain regions it may be mentioned that Mr. Burnham very recently discovered eighteen new nebulæ in a small area of 16′ by 5′·5 near the position in R.A. 13^h 38^m, Dec. 56° 20′ N. Near the pole of the northern heavens there exist many unrecorded nebulæ, as this region does not appear to have been thoroughly examined with a large instrument. It is often the case that several nebulæ are clustered near together. Whenever a new one is discovered the surrounding space should therefore be carefully surveyed in search of others. The region immediately outlying known objects may also be regarded as prolific ground for new discoveries. After several hours’ employment in the work of searching for nebulæ or comets the eye is enabled to discern faint objects which were invisible at first, as it is in a better condition to receive feeble impressions. While comet-seeking in 1889 and 1890 I discovered ten new nebulæ, all near the N. pole, and their approximate positions are given below:—

+————+————————————-+——————————————-+————————————————————————————--+ |Ref.|Date of |Position 1890. | | |No. |Discovery. +——————-+——————-+ Description | | | |R.A. | Dec. +| | +————+————————————-+——————————————-+————————————————————————————--+ | | |h m s | ° ′ | | | 1. |1889, Aug. 26|4 29 59|75 25·2|F., S., b. M., *12, n.p. | | 2. |1890, Nov. 7 |4 40 19|78 7·9 |F., S., R. | | 3. |1890, Oct. 19|4 46 38|68 9·8 |F., S., R., b. M.N., F. double| | | | | | * s.f. | | 4. |1890, Nov. 16|5 50 7 |80 31·0| v.F., S. | | 5. |1890, Nov. 9 |6 11 45|83 1·9 |F., S., R., m. b. M. | | 6. |1890, Oct. 17|6 59 26|85 45·0|v. F., v.v.S., 12′ s.s.f. | | | | | | N.G.C. 2300 | | 7. |1890, Nov. 7 |7 8 52 |80 7·4 |v. F., p. S., 22′ s. s. f. | | | | | | N.G.C. 2336. | | 8. |1890, Sept.14|7 23 24|85 30·0|F., S., E., 46′ s. f. N.G.C. | | | | | | 2300. | | 9. |1890, Sept. 8|8 21 37|86 7·4 |p. F., S., m. b. M., * n. f. | | 10.|1890, Aug. 23|8 34 30|85 54·4|F., S., R., g. b. M., near | | | | | | preceding. | +————+————————————-+——————————————-+———————————————————————————-—-+

Abbreviations:—F., faint; S., small; R., round; M., middle; N., nucleus, E., extended; v., very; b., brighter; n., north; s., south; f., following; p., pretty, preceding; m., much; g., gradually; *, star; N.G.O., New General Catalogue.

No. 8 is placed centrally within a curious semicircle of stars, thus:—

I.—CLUSTERS OF STARS.

+————————-+——————-+——————————————————+———————————————————————————————+ | | | Position, 1890. | | | No. | No. +————————-+————————+ | | N.G.C., | M., | | | Description. | | 1888. | 1781. | R.A. | Dec. | | +————————-+——————-+—————————+————————+———————————————————————————————+ | | | | | | | | | h m | ° ′ | | | 225. | | 0 37·1 | +61 3 | Stars 9th-10th mags. Between | | | | | | γ and κ Cassiopeiæ. | | 869. | | 2 11·3 | +56 38 | In Perseus. Stars 7th-14th | | | | | | mags. | | 1039. | 34. | 2 35·0 | +42 18 | A fine group, chiefly of 9th | | | | | | mag. stars. | | 1912. | 38. | 5 21·3 | +35 44 | Stars of various mags. In | | | | | | Auriga. | | 1960. | 36. | 5 29·0 | +34 4 | Stars of 9th-11th mags. Near | | | | | | 1912. | | 2099. | 37. | 5 45·1 | +32 31 | Stars and star-dust. 5° S. of | | | | | | θ Aurigæ. | | 2168. | 35. | 6 2·0 | +24 21 | Stars of 9th-16th mags, near | | | | | | ζ Geminorum. | | 2287. | 14. | 6 42·3 | -20 38 | Visible to naked eye. 4° S. of| | | | | | Sirius. | | 2437. | 46. | 7 36·8 | -14 34 | Nebula involved with cluster | | | | | | of 8th-13th mag. stars. | | 2477. | | 7 48·4 | -38 16 | Fine group of 12th mag. stars | | | | | | near ζ Argûs. | | 2516. | | 7 56·5 | -60 34 | Visible to naked eye. 200 | | | | | | stars of 7th-13th mags. | | 2547. | | 8 7·4 | -48 56 | Vis. n.e. Stars 7th-16th mags.| | | | | | Diameter 20′. | | 2548. | | 8 8·3 | -5 28 | Stars of 9th-13th mags. In | | | | | | Monoceros. | | 2632. | 44. | 8 34·0 | +20 22 | Præsepe. Group of bright stars| | | | | | vis. n. e. | | 2682. | 67. | 8 45·2 | +12 13 | Large group of stars of | | | | | | 10th-15th mags. | | 4755. | | 12 47·1 | -59 45 | Very large group about κ | | | | | | Crucis. | | 6121. | 4. | 16 16·9 | -26 16 | Close to Antares. Group and | | | | | | line of stars through it. | | 6603. | 24. | 18 12·0 | -18 28 | Stars of 15th mag. 3° N. of | | | | | | μ Sagittarii. | | 6611. | 16. | 18 12·7 | -13 50 | Group of at least 100 stars | | | | | | of various mags. | | 6705. | 11. | 18 45·1 | -6 24 | Stars of 11th mag. and | | | | | | fainter. Fine object. | | 6838. | 71. | 19 48·8 | +18 29 | Stars of 11th-16th mags. In | | | | | | Sagitta. | | 7243. | | 22 10·9 | +49 20 | A clustering of many bright | | | | | | stars. | | 7654. | 52. | 23 19·4 | +61 0 | Irregular group of 9th-13th | | | | | | mag. stars. | | 7789. | | 23 51·5 | +56 6 | Grand cluster of 11th-18th | | | | | | mag. stars. | +————————-+——————-+—————————+————————+———————————————————————————————+

II.—Globular Clusters of Stars.

+————————-+——————-+——————————————————+———————————————————————————————+ | | | Position, 1890. | | | No. | No. +————————-+————————+ | | N.G.C., | M., | | | Description. | | 1888. | 1781. | R.A. | Dec. | | +————————-+——————-+—————————+————————+———————————————————————————————+ | | | | | | | | | h m | ° ′ | | | 104. | | 0 19·1 | -72 42 | Very large; more than 15′ | | | | | | diameter. | | 288. | | 0 47·8 | -27 11 | Slightly elliptical. Stars | | | | | | 12th-16th mags. | | 362. | | 0 58·5 | -71 26 | Stars 13th-14th mags. | | | | | | Diameter 4′. | | 1261. | | 3 9·3 | -55 38 | Large. Stars and star-dust. | | | | | | | | 1851. | | 5 10·5 | -40 10 | Very bright and large. Fine | | | | | | object. | | 4147. | | 12 4·5 | +19 9 | Pretty large, round. Minute | | | | | | stars. | | 4590. | 68. | 12 33·7 | -26 9 | Much compressed group of 12th | | | | | | mag. stars. | | 5024. | 53. | 13 7·5 | +18 45 | Fine object. Chiefly 12th | | | | | | mag. stars. | | 5139. | | 13 20·2 | -46 44 | Very large; diameter 20′. | | | | | | At ω Centauri. | | 5272. | 3. | 13 37·1 | +28 56 | Visible to naked eye. | | | | | | Diameter 7′. | | 5634. | | 14 23·8 | - 5 29 | Very bright, considerably | | | | | | large. Round. | | 5904. | 5. | 15 13·0 | + 2 29 | Visible naked eye. Stars | | | | | | 11th-15th mags. Diam. 5′. | | 5986. | | 15 38·8 | -37 25 | Stars of 13th-15th mags. In | | | | | | Lupus. | | 6093. | 80. | 16 10·5 | -22 42 | Stars of 14th mag. Between | | | | | | α and β Scorpii. | | 6205. | 13. | 16 37·7 | +36 40 | Visible naked eye. A grand | | | | | | object, in Hercules. | | 6218. | 12. | 16 41·5 | - 1 45 | Stars of 10th mag. and | | | | | | fainter. Diam. 4′. | | 6254. | 10. | 16 51·4 | - 3 56 | Stars of 10th-15th mags. | | | | | | Diameter 4′. | | 6266. | 62. | 16 54·2 | -29 57 | Stars of 14th-16th mags. In | | | | | | Scorpio. | | 6333. | 9. | 17 12·8 | -18 24 | Much compressed group of | | | | | | 14th mag. stars. Diam. 4′. | | 6341. | 92. | 17 13·8 | +43 15 | A mass of stars and star-dust.| | | | | | 7° N, π Herculis. | | 6402. | 14. | 17 31·8 | - 3 11 | Chiefly stars 15th mag. | | | | | | Diameter 4′. | | 6656. | 22. | 18 29·7 | -24 0 | Stars of 11th-15th mags. | | | | | | In Sagittarius. | | 6779. | 56. | 19 12·3 | +30 0 | Stars 11th-14th mags. Between | | | | | | β Cygni and γ Lyræ. | | 6809. | 55. | 19 33·0 | -31 14 | Fine, large, round cluster of | | | | | | stars 11th-13th mags. | | 7078. | 15. | 21 24·7 | +11 41 | Group of stars and star-dus. | | | | | | Diameter 5′. | | 7089. | 2. | 21 27·8 | - 1 19 | Exceedingly small stars. | | | | | | Diameter 5′. | | 7099. | 30. | 21 34·1 | -23 41 | Stars 12th-16th mags. | | | | | | Diameter 3′. | +————————-+——————-+—————————+————————+———————————————————————————————+

III.—NEBULÆ.

+————————-+——————-+——————————————————+———————————————————————————————+ | | | Position, 1890. | | | No. | No. +————————-+————————+ | | N.G.C., | M., | | | Description. | | 1888. | 1781. | R.A. | Dec. | | +————————-+——————-+—————————+————————+———————————————————————————————+ | | | | | | | | | h m | ° ′ | | | 185. | | 0 32·9 | +47 44 | Very large; pretty bright. | | | | | | Resolvable into stars. | | 224. | 31. | 0 36·7 | +40 40 | Great nebula in Andromeda. | | | | | | | | 253. | | 0 42·2 | -25 54 | Very, very large and bright. | | | | | | 24′ by 3′. | | 598. | 33. | 1 27·6 | +29 57·1| Exceedingly bright and large.| | | | | | Nucleus. | | 650. | 76. | 1 35·4 | +51 1 | Very bright double nebula. | | | | | | | | 1365. | | 3 29·4 | -36 30 | Very bright and large. | | | | | | Elliptical. | | 1501. | | 3 57·5 | +60 37 | Pretty bright planetary | | | | | | nebula. Diam. 1′. | | 1514. | | 4 2·4 | +30 29 | Star of 9th mag. in nebula 3′ | | | | | | diameter. | | 1952. | 1. | 5 27·9 | +21 56 | Great Crab Nebula, near | | | | | | ζ Tauri. Stars. | | 1976. | 42. | 5 29·9 | - 5 28 | Great nebula involving θ | | | | | | Orionis. | | 1990. | | 5 30·6 | - 1 16 | Star (ε Orionis) involved in | | | | | | nebulosity. | | 2070. | | 5 39·5 | -69 9 | Visible to naked eye. Great | | | | | | “looped” nebula. | | 2392. | | 7 22·7 | +21 8 | Nebulous star of 9th mag. | | | | | | | | 2403. | | 7 26·2 | +65 50 | Very large and bright. | | | | | | Elliptical. | | 2655. | | 8 41·2 | +78 38 | Very bright. Condensed in the | | | | | | middle. | | 2681. | | 8 45·6 | +51 44 | Very large and bright. | | | | | | Centre = star 10th mag. | | 2683. | | 8 45·9 | +33 51 | Very large and bright. | | | | | | Elliptical. | | 2841. | | 9 14·4 | +51 26 | Very large and bright. | | | | | | Centre = star 10th mag. | | 2903. | | 9 25·9 | +22 0 | Large, elliptical, double | | | | | | nebula. | | 3031. | 81. | 9 46·5 | +69 35 | Exceedingly bright and large. | | | | | | Elliptical. | | 3034. | 82. | 9 46·7 | +70 13 | A bright ray. In field with | | | | | | preceding. | | 3242. | | 10 19·5 | -18 5 | Bright planetary nebula. | | | | | | Diameter 45″. Blue. | | 3372. | | 10 40·8 | -59 6 | Great nebula surrounding | | | | | | ζ Argûs. | | 3556. | | 11 5·4 | +56 16 | Large, rather bright. | | | | | | Elliptical. | | 3587. | 97. | 11 8·4 | +55 37 | Fine planetary nebula. Diam. | | | | | | 3′.Near β Ursæ Majoris. | | 3623. | 65. | 11 13·2 | +13 42 | Large, bright, elliptical. | | | | | | Near following one. | | 3627. | 66. | 11 14·5 | +13 36 | Large elliptical nebula. Near | | | | | | β Leonis. | | 4254. | 99. | 12 13·3 | +15 2 | Very fine 3-branched spiral | | | | | | nebula. | | 4321. | 100. | 12 17·4 | +16 26 | Very large 2-branched spiral | | | | | | nebula. | | 4382. | 85. | 12 19·9 | +18 48 | Very bright; pretty large. | | | | | | Round. | | 4472. | 49. | 12 24·2 | + 8 37 | Bright; round. Resolvable into| | | | | | stars. | | 4486. | 87. | 12 25·3 | +13 0 | Large; round. Bright centre. | | | | | | Third of three. | | 4565. | | 12 30·9 | +26 36 | A ray of bright nebulosity E. | | | | | | of Coma. | | 4736. | 94. | 12 45·7 | +41 43 | Large and bright. Nucleus. | | | | | | Resolvable. | | 5128. | | 13 19·0 } -42 27 | Very large and bright. | | | | | | Elliptical. Bifid. | | 5194. | 51. | 13 25·2 | +47 46 | Great spiral nebula near | | | | | | ζ Ursæ Maj. | | 5236. | 83. | 13 30·8 | +29 18 | Fine object. 3-branched | | | | | | spiral. | | 5367. | | 13 51·1 | -39 27 | Very large and bright. | | | | | | Condensed in the middle. | | 5907. | | 15 13·0 | +56 44 | Large, elliptical. Another | | | | | | very close to it. | | 6369. | | 17 22·6 | -23 40 | Pretty bright, small | | | | | | ring-nebula. | | 6514. | 20. | 17 55·7 | -23 1 | Bright; large. Trifid. Double | | | | | | star involved. | | 6523. | 8. | 17 56·9 | -24 23 | Bright, with loose cluster of | | | | | | stars. | | 6618. | 17. | 18 14·4 | -16 13 | Bright and extremely large. | | | | | | 2-hooked. | | 6720. | 57. | 18 49·5 | +32 54 | Ring-nebula between β and | | | | | | γ Lyræ. | | 6826. | | 19 41·8 | +50 16 | Pretty large and bright | | | | | | planetary nebula. | | 6853. | 27. | 19 54·9 | +22 25 | The “Dumb-bell” Nebula. Fine | | | | | | object. | | 6960. | | 20 41·1 | +30 19 | Large and bright, κ Cygni | | | | | | involved. | | 7009. | | 20 58·2 | -11 48 | Very bright, small, planetary | | | | | | nebula. Elliptical. | | 7662. | | 23 20·6 | +41 56 | Very bright, pretty small, | | | | | | planetary or ring-nebula. | +————————-+——————-+——————————————————+———————————————————————————————+

FOOTNOTES:

Sir W. Herschel at first entertained this view, finding that with every increase of telescopic power more nebulæ were resolved. But in 1791 he said, “perhaps it has been too hastily surmised that all milky nebulosity is owing to starlight only.” Lacaille had remarked in 1755 that “it is not certain the whiteness of parts of the Milky Way is caused by clusters of stars more closely packed together than in other parts of the heavens.”

This is exclusive of 47 new nebulæ discovered by Prof. Safford, which form the appendix to the catalogue.

Chambers says only four examples are known, but this is erroneous, as Lord Rosse’s telescope has added five ring-nebulæ to the four previously catalogued.

Some of the nebulæ in Messier’s list were discovered by Mechain at Paris, who, like Messier, earned celebrity by his cometary discoveries. He was born at Laon in 1744, and died at Valencia in 1805.

O. Struve had expressed views identical with these in 1857 (see ‘Monthly Notices,’ vol. xvii. p. 230).

Humboldt says this “name is evidently derived from the voyage of Magellan, although he was not the first who observed them.”

I have selected the various objects in these lists from the New General Catalogue.

These forms are more numerous than the annular nebulæ. They often exhibit a blue colour, and the spectroscope shows them to consist of gas.

NOTES AND ADDITIONS.

LARGE AND SMALL TELESCOPES.

P. 19.—With reference to mountainous sites for large instruments, a remark in Sir Isaac Newton’s ‘Opticks’ (1730) may be quoted:—“Telescopes ... cannot be formed so as to take away that confusion of rays which arises from the tremors of the atmosphere. The only remedy is a most serene and quiet air, such as may perhaps be found on the tops of the highest mountains above the grosser clouds.”

P. 27.—Lieut. Winterhalter, of the United States Navy, recently visited a large number of European observatories, and in describing that of Nice says:—“M. Perrotin declares that two hours’ work with a large instrument is as fatiguing as eight with a small one, the labour involved increasing in proportion to the cube of the aperture, the chances of seeing decreasing in the same ratio, while it can hardly be said that the advantages increase in like proportion.” The Nice Observatory, and its splendid instruments (including a 30-inch refractor), are due to the munificence of M. Bischoffsheim, who has expended about five million francs upon them.

P. 36.—The large refractor to be erected on Wilson’s Peak of the Sierra Madre range of mountains, in Southern California, is to be 40 inches in diameter. The rough unground disks of glass are already in the hands of the Clarkes, of Cambridgeport, Mass. It is estimated that the complete object-glass and cell will cost something like $65,000, and the focal length of the instrument will be about 58 feet.

THE SUN.

P. 100.—The last minimum of sun-spot frequency appears to have occurred at the middle of 1889. Conspicuous spots were very rare in the first half of 1890, but some fine groups were presented in the last half of the year. On Aug. 31 I saw a group extending over 113,000 miles in length, and on Nov. 27 there was another, which measured 123,700 miles.

P. 111.—Thompson’s cardboard disks have been favourably spoken of as enabling observers to determine the positions of spots at any season of the year.

MERCURY.

P. 137.—At the meeting of the British Astronomical Association on Nov. 26, 1890, Mr. G. F. Chambers expressed his firm belief in the existence of an intra-Mercurial planet. The President (Capt. W. Noble) in his inaugural address pointed out the desirability of effecting further observations, both of Mercury and Venus, with a view to redetermine their rotation-periods. He justly remarked that moderately small instruments might be fittingly employed in the work, and that Schiaparelli’s deductions (mentioned on pp. 142 and 149) ought to be accepted with extreme reserve pending their verification.

MARS.

P. 160.—Prof. W. H. Pickering observed some of the canals on Mars in 1890 with a 12-inch refractor, but was not able to double any of them. He says that, in examining these objects, the power employed should not “exceed one or two hundred.” This is quite contrary to the advice of others, who recommend high magnifiers; and perhaps it accounts for Prof. Pickering’s failure in recognizing the duple canals.

With the great 36-inch refractor Mr. Keeler saw, on July 5 and 6, 1890, some curious white spots on the edges of the gibbous limb of Mars, something similar to those visible on the unilluminated part of the lunar disk. The canals were observed as feeble diffused bands. The two satellites were seen by a lady visitor, though previously unaware of their existence.

P. 161.—The method of deriving the rotation-period of Mars is exemplified by Mr. Proctor in the ‘Monthly Notices,’ vol. xxviii. p. 38. An interesting paper, “On the Determination of the Rotation-Period of Jupiter in 1835,” will be found in the ‘Memoirs,’ vol. ix.

PLANETOIDS.

P. 167.—The 308th planetoid was discovered by Charlois on March 5, 1891.

JUPITER.

P. 170.—Dupret, in Algiers, saw Jupiter with the naked eye on Sept. 26, 1890, and following days, twenty minutes before sunset.

P. 191.—M. Guillaume, during a recent transit of the shadow of Jupiter’s second satellite, observed a duplicate shadow, fainter than the ordinary one, which partly covered its southern side.

COMETS.

P. 250.—On Nov. 16, 1890, Dr. Spitaler, while looking for Zona’s Comet with the 27-inch refractor of the Vienna Observatory, discovered a new and very faint comet only 23′ distant from the object of his search. That two of these bodies should be found almost simultaneously and so near together must be regarded as a very singular coincidence.

METEORS.

P. 261.—Mr. Proctor held the view that certain meteorites may have originally been ejected from the Sun. A recent writer thus summarizes our knowledge of them:—“That they are independent bodies, moving in orbits of their own in space; that these dark bodies are abundant in the interplanetary spaces; that those within the near range of solar or planetary attraction move with great velocity; that many swarms of them follow well-known orbits; and that, in general, their origin is undoubtedly the same as that of other celestial bodies” (‘Sidereal Messenger,’ June 1890, p. 284).

P. 267.—On May 2, 1890, a brilliant fireball, leaving a long train of fire and smoke, and exploding with a noise like thunder, was seen at many places in Northern Iowa, Minnesota, U.S.A. Some fragments of the meteor fell on a farm a few miles from the south line of Minnesota. The largest piece was sold by auction for $100, but it soon transpired that the person who sold it was only the lessee and not the owner of the ground on which the meteor fell. The aerial visitor and its purchase-money were therefore peremptorily seized by legal authorities, pending the decision of a Court of Justice as to the rightful ownership.

P. 267.—On December 14, 1890, at 9^h 42^m a large fireball of dazzling lustre, and giving a report like thunder, was widely observed in the southern parts of England. At the end-point the fireball appears to have been only 8 miles in height, and over a point near Brentwood, in Essex.

THE STARS.

P. 309.—Prof. Chandler, of Cambridge, Mass., estimates that the total number of variable stars visible with a common field-glass is about 2000, but with a large telescope there are probably hundreds of thousands within reach. He further states that quite five sixths of the variable stars are reddish in colour, and that the redness is usually a function of the length of the period of variation. The redder the star the longer its period.

P. 312.—In a recent communication to the Academy of Sciences, M. Lescarbault (the alleged discoverer of Vulcan in 1859) announced that on the night of January 11, 1891, he discovered a bright body in Leo which he could not identify in any star-map, and hence concluded it to be a new star, or one suddenly increased in brilliancy. The “new star,” however, subsequently turned out to be the planet Saturn! This ridiculous mistake (so easily avoidable with a little care) will naturally divest the supposed discovery of Vulcan of the importance attached to it by some writers, for M. Lescarbault obviously lacks the experience and caution necessary to command credit.

NEBULÆ AND CLUSTERS OF STARS.

P. 327.—Mr. Roberts, from a comparison of his photographs, has found distinct evidence of variability in the nucleus of the great nebula in Andromeda. In some of the photographs the nucleus is shown to be stellar, while in others there is no trace of this. Mr. Roberts remarks:—“We may reasonably infer that the nucleus of the nebula is variable, and that it will be practicable to study the character of the variability without the necessity of giving long exposures of the plates.” The period of the variation has now to be determined, and it is advisable that telescopic observations of the nucleus should be made with the view of confirming the photographic results. It would be premature to regard the changes as demonstrated before they have been submitted to thorough investigation.

P. 327.—In the Comptes Rendus for March 2, 1891, M. Bigourdan has a paper on the variability of the nebula N.G.C. 1186, situated near Algol. This nebula was discovered by Sir W. Herschel in 1785, and though Sir J. Herschel re-observed it in 1831, Lord Rosse looked for it without success in 1854 and 1864. On Nov. 8, 1863, D’Arrest failed to detect the nebula, though he searched for it with assiduity at a time when the sky was very favourable. He was led to conclude that the object did not exist. M. Bigourdan finds that the nebula is again visible in the position indicated by the two Herschels, viz. R.A. 2^h 54^m 20^s, Dec. +42° 10′, he having observed it on Jan. 31 and Feb. 26, 1891. It is difficult to believe that this object could have escaped the scrutiny of Lord Rosse and D’Arrest in 1854, 1863, and 1864; hence the variation is probably real. The nebula may be easily found, as it is very near the binary B.D. +42° (1123 G.C.), the position of which for 1891 is R.A. 2^h 58^m 6^s, Dec. +42° 29’ (‘Nature,’ March 12, 1891).

P. 329.—While examining the Pleiades on the night of November 14, 1890, Mr. Barnard discovered a new and considerably bright, round, cometary nebula 36″ S. and 9″ following Merope. The reason why this nebula has not been detected by photography is because it is so near Merope that the over-exposed light from the star obliterates it. But it is certainly very strange that the object alluded to has never been telescopically discovered before; for the Pleiades have been scrutinized repeatedly with all sorts of telescopes, and particularly since Tempel announced his discovery of a large faint nebula involving Merope in 1859. Mr. Barnard says the new nebula is 30″ in diameter, and that it is visible in a 12-inch refractor when Merope is hidden with a wire.

INDEX.

Action in Sun-spots, Cyclonic, 108.

Active volcanoes on the Moon, 120.

Adams theoretically discovers Neptune, 222.

Advantage of Equatoreals, 54.

Aerolites, 264.

Air and water on the Moon, Absence of, 115.

Algol, 310.

Alleged satellite of Venus, 152.

Almanacks, 83.

Alphabet, Greek, 287.

Alpine Valley, 127.

Altitudes of markings on Jupiter, 185.

Amateur’s first view of Mercury, 139.

Ancient ideas concerning meteors, 260.

Andromeda, Great Nebula in, 334.

Andromedes, 276.

Angles of Position, Measurement of, 291, 306.

Announcement of a new comet, 244.

Annual rate of cometary discoveries, 255.

Antares, 309.

Anthelme, Discoverer of a new star in 1670, 313.

Apennines, 132.

Aperture and Power required for Comet-seeking, 252.

Apparitions, Meteoric, 261.

Appearance of Comets, 228.

—— of Mars, 155.

Aquarids, 275.

Archimedes, 127.

Argelander’s magnitudes of stars, 294.

Aristarchus, 120.

Ascertaining positions of Comets, 257.

Aspect of the rings of Saturn, 204.

Atmosphere of Jupiter, 177.

—— of Mars, 161.

—— of Mercury, 139.

—— of Venus, 151.

Atmospheric undulations, 29.

Attractions of Telescopic work, 85.

Auwers, Discoverer of a new star in 1860, 314.

Bacon, Roger, Early hints on refracted rays, 3.

Barnard, His cometary discoveries, 255.

—— observes Brooks’s multiple Comet, 239.

—— observes new stars in the Trapezium, 319.

—— observes a new nebula in the Pleiades, 351.

Beauty and brilliancy of Venus, 145,

Belts of Sun-spots, 104,

—— on Jupiter, 172.

—— on Saturn, 198.

—— on Uranus, 218.

Berthon’s dynamometer, 50.

Biela’s Comet, 238.

Bigourdan observes a variable Nebula, 351.

Binary Stars, 300.

Birmingham discovers a new star in 1866, 314.

Bond, G. P., discovers Crape-ring of Saturn, 202.

Brahe’s, Tycho, new star of 1572, 312.

Bright objects near the Sun, 107.

Brightness and position of Jupiter, 170.

Brooks on Comet-seeking, 253.

—— on Occultation of Jupiter, 187.

—— on Shower of telescopic Meteors, 272, 274.

Brooks’s double Comet of 1889, 239.

Brorsen’s Comet, 239.

Browning and reflecting-telescopes, 60.

Brunowski discovers a new star, 313.

Burnham, Discoverer of double Stars, 31, 320.

—— discovers a group of 18 new nebulæ, 341.

——, Measures of the companion to Sirius, 307.

—— on the inutility of “stops,” 58.

Calver compares light of reflectors and refractors, 37.

——, Maker of glass specula, 16, 17.

Canal-shaped markings on Mars, 159.

Canis Majoris α, 307.

Cassegrain’s reflecting-telescope, 10.

Cassini, Diameter of his object-glasses, 9.

—— discovers four satellites and the divided ring of Saturn, 9.

——, Observations of Jupiter, 172.

——, —— of Saturn, 198.

——, —— of Venus, 147.

Celestial Globe, 63.

Centauri α, Diameter and distance, 299.

Ceres, 168.

Chambers on Coloured Stars, 316.

—— on the intra-Mercurial Planet, 348.

Chandler on Variable Stars, 350.

Changes, Lunar, 120.

—— on Jupiter, 182.

—— on Mars, 163.

—— on Saturn, 206.

Charts of Mars, 158.

Cheapness of Telescopes, 57.

Choice of Telescopes, 38.

Clark, Alvan, & Sons, make large object-glasses, 18.

——, discovers the companion to Sirius, 307.

Cleaning lenses, 59.

Clusters of Stars, 317.

Coggia’s Comet of 1874, 233.

Colour of Jupiter, 171.

—— of Mars, 155.

—— of Saturn, 195.

—— of Uranus, 217.

Colouring of the eclipsed Moon, 119.

Colours of Stars, 315.

Coma Berenices, 317.

COMETS AND COMET-SEEKING, 227. Ideas concerning Comets, 227. Appearance of Comets, 228. Large number visible, 228. Nature of apparition, 229. Tenuity, 229. Differences of orbit, 230. Discoveries of Comets, 230. Large Comets, 231. Periodical Comets, 234. Halley’s Comet, 236. Encke’s Comet, 236. Biela’s Comet, 238. Brooks’s double Comet, 239. Brorsen’s Comet, 239. Faye’s Comet, 240. D’Arrest’s Comet, 240. Pons-Winnecke’s Comet, 240. Tuttle’s Comet, 241. Grouping of Periodical Comets, 241. Further Observations required, 243. Nomenclature of Comets, 246. Curiosities of Comets, 248. Naked-eye Comets, 248. Comet-seeking, 249. English weather and Comet-seeking, 251. Aperture and Power required, 252. Annual rate of discovery, 255. Telescopic Comets, 256. Ascertaining positions, 257. Dr. Doberck’s hints, 258. Prizes for Discoveries, 258.

Common, His large Reflectors, 15; Their performance, 28.

Computation of a Meteor’s real path, 278.

Conjunctions, Planetary, 225.

Constellation figures, The, 290.

Cooke & Sons mount a 24·8-inch refractor, 18; Its barren record, 25.

Copernicus, 127.

Course of the Milky Way, 296.

“Crab” Nebula in Taurus (M. 1), 336.

Crape-ring of Saturn, 202.

Crucis κ, Cluster at, 318.

Curiosities of Comets, 248.

Cyclonic action in Sun-spots, 108.

Cygnus, Nebulous streams in, 339.

Dallmeyer on Dividing power, 293.

D’Arrest’s Comet, 240.

Dawes’s observations of Jupiter, 173.

—— observations of Saturn’s Crape-ring, 202.

——, On Dividing power, 292.

—— Solar Eyepiece, 92.

Definition in towns, 81.

Deimos, Outer Satellite of Mars, 165.

Democritus explains the Milky Way, 2.

Dennett announces the Red Spot on Jupiter, 173.

Denning’s Comet, 243.

Denza on the Meteors of Nov. 27, 272.

Derham, his list of Nebulæ, 327.

Description of Nebulæ and Clusters of Stars, 333.

Determination of the Sun’s rotation-period, 104.

Detonating Fireballs, 267.

Dewing of Mirrors, 62.

Diffraction-rings, 293.

Dimensions of Nebulæ and Scar-clusters, 332.

—— of Sun-spots, 94.

Disappearance of Saturn’s ring, 205.

Discordant observations of Saturn, 204.

Discoveries of Comets, 230.

—— of Nebulæ, 341.

Discovery of Neptune, 221.

—— of Planetoids, 167.

—— of Uranus, 215.

Distance of the stars, 299.

Distinction between Nebulæ and Star-clusters, 324.

Distribution of Nebulæ in R.A., 326.

Disturbances, Recurrent solar, 110.

Dividing power, 292.

Divisions in outer ring of Saturn, 201.

Doberck, Dr., On the Invention of the Telescope, 5.

——, On Comet-seeking, 258.

Dollond patents his Achromatic Telescope, 12.

——, His object-glasses, 16.

Donati’s Comet of 1858, 233.

Dörfel mountains, 131.

Double Comets:— Biela’s, 238. Brooks’s, 239.

—— Nebulæ, 332.

—— Stars, 300, 302.

Draco, planetary nebula in, 335.

Drawing, 73.

Drawings of Jupiter, 185.

Dumb-bell Nebula (M. 27), 337.

Duration of meteor-flights, 282.

Duration of Silver-on-glass films, 60.

Dynamometer, Berthon’s, 50.

Early observations of Jupiter, 172.

—— —— of nebulæ and star-clusters, 326.

—— —— of Neptune, 222.

—— —— of Saturn, 197.

—— —— of the Sun, 88.

—— —— of Uranus, 216.

—— —— of Venus, 147.

Earthshine on the Moon, 116.

Eccentric position of Saturn’s rings, 204.

Eclipses of Jupiter’s satellites, 189.

—— of the Moon, 118.

—— of the Sun, 97.

Elger’s lunar observations, 127, 131.

—— Drawings of lunar objects, 129, 130, 132.

Ellipse, 230.

—— on Jupiter, Gledhill’s, 173.

Elliptical nebulæ, 338.

Elongations of Mercury, 138.

—— of Venus, 145.

Encke’s Comet, 236.

—— division in Saturn’s ring, 202, 208.

English weather and Comet-seeking, 251.

Equatoreal spots on Jupiter, Bright, 175, 181.

—— ——, Dark, 181.

Equatoreals, Advantage of, 54.

Exceptional position of Sun-spots, 111.

Eyepiece, Field of, 50.

Eyepieces, 46.

——, Single-lens, 47.

Fabricius observes Sun-spots, 89.

Faculæ, Sudden outburst of, 108.

Faint objects, Observation of, 72.

Faintness of the markings on Venus, 150.

Falls of stone and iron, 266.

Faye’s Comet, 240.

Field of eyepiece, Diameter of, 50.

Figures, The Constellation, 290.

Fireball of Nov. 23, 1877, 267.

Fireballs, 267.

——, Heights of, 268.

First view of Mercury, Amateur’s, 139.

Formations, Lunar, 123.

Foucault parabolizes and silvers glass Speculæ, 15.

Fracastor, His remarks on lenses in 1538, 4.

Friendly Indulgences, 74.

Future, Past and, 84.

Future eclipses of the Moon, 118.

—— —— of the Sun, 98.

Galaxy, or Milky Way, The, 295.

Galilei and the invention of the Telescope, 2, 4, 5.

——, Discovery of Jupiter’s satellites, 187.

——, His first instrument and discoveries, 6, 7.

Galle observes Saturn’s crape-ring, 202.

—— observes Neptune, 222.

Geminids, 276.

Glass, Opera, 61.

Gledhill’s ellipse on Jupiter, 173.

Globe, Celestial, 63.

Globular clusters. 338.

—— ——, List of, 344.

Gore, Diameter of α Centauri, 299.

——, Dimensions of a Star-cluster, 332.

——, Stellar distribution, 294.

Greek alphabet, 287.

Gregory invents a reflecting-Telescope, 10.

Grimaldi, 129.

Grouping of periodical Comets, 241.

Groups of Stars, 316.

Grubb, Maker of a 4-foot Cassegrainian reflector, 14; Performance of, 25.

——, Maker of a 27-inch refractor, 18; Performance of, 27.

Hall, Chester More, invents achromatic Object-glass, 11.

Hall, Prof., discovers a white spot on Saturn, 199.

——, Observations of Saturn’s satellites, 213.

—— on the great Washington refractor, 26.

——, Remarks on large and small telescopes, 31.

Halley’s Comet, 236.

—— list of Nebulæ in 1716, 326.

Harriot, Early observer of Sun-spots, 89, 90.

Hartwig, Discovers a new Star in Andromeda, 315.

Heights of Fireballs, 268; of Meteors, 277.

Heis, His labours in Meteoric astronomy, 262.

Hencke, Discoverer of Planetoids, 167.

Henry, Bros., make a 30-inch refractor, 18; Performance of, 27.

—— observe the belts on Uranus, 218.

Herschel, Prof. A. S., observes meteors, 262.

Herschel, Sir J., Comet of 1861, 233.

——, Description of k Crucis, 318.

——, Disappearance of Saturn’s ring, 205.

——, Rediscovers Uranus, 219.

——, Satellites of Uranus, 220,

——, Texture of Comets, 229.

——, Thickness of Saturn’s ring, 205.

——, Trapezium of Orion, 318, 320.

Herschel, Sir W., and Cometary discovery, 231.

——, His discovery of Nebulæ, 327.

——, His discovery of nebulous Stars, 330.

——, His discovery of Uranus, 215; of Satellites, 220.

——, His method of observing Sun-spots, 91.

——, His observations of Jupiter, 182.

——, His observations of Mercury, 142.

——, His observations of Saturn, 199.

——, His observations of Venus, 149.

——, Nucleus of Comet of 1811, 232.

—— observes Binary Stars, 300, 306.

——, Performance of 4-ft. reflector, 21.

——, Remarks on eyepieces, 47.

——, Rotation of Jupiter’s Satellites, 189.

——, Singular figure of Saturn, 196.

Herschel’s, Sir W., Telescopes, 12, 13, 39.

Hevelius, diameter of his object-glasses, 9.

Hind, Discoverer of a new Star in 1848, 314.

——, Discoverer of Planetoids, 167.

——, Discoverer of a variable Nebula, 328.

Hipparchus forms a Star-catalogue, 312.

Hoek on the origin of Comets, 243.

Hooke’s observations of Jupiter, 172.

Hough’s observations of Jupiter, 174, 182.

Howlett’s observations of Sun-spots, 101, 102.

Huygens on the invention of the Telescope, 2.

——, Discoveries on Saturn, 8, 198.

——, Length of his instruments, 8.

Huygens’s Negative eyepiece, 8, 46.

Hyginus, The rill or cleft of, 130.

Hyperbola, 230.

Identity of Meteors and Comets, 262.

Increasing number of Telescopes, 57.

Intra-Mercurial Planet, 137.

Jansen, Zachariah, Inventor of the Telescope, 4.

Johnson’s projections of Solar Eclipses, 99.

Juno, 168.

JUPITER, 170. An interesting object, 170. Brightness and position, 170. Period &c., 171. Belts and spots, 172. Observations of Hooke, Cassini, and others, 172. The “Ellipse” of 1869-70, 173. The red spot, 173. Rotation of red spot, 175. Rotation of bright equatoreal spots, 175. Rotation of dark spots in N. hemisphere, 175. Rotation-period, 176. Nature of the red spot, 177. Bright equatoreal spots, 181. Dark equatoreal spots, 181. New belts, 182. Changes on the planet, 182. Further observations required, 183. Occultations by the Moon, 185. The four satellites, 187. Their eclipses, occultations, and transits, 189. The planet without visible satellites, 192. Spots on the Satellites, 193. Occultation of a Star by Jupiter, 193.

Keeler, White spots and canals on Mars, 348.

Kitchiner, The inutility of large Telescopes, 35.

——, Singular form of Saturn, 196.

Klein’s supposed new crater near Hyginus, 122.

Large and small telescopes compared, 20.

—— Comets, 231.

—— number of Comets, 228.

—— refractor intended for California, 36, 347.

Lassell, His large reflecting-telescopes, 14; Their performance, 24.

—— discovers the satellite of Neptune, 224.

—— glimpses a belt on Uranus, 217.

Leander McCormick refractor, 26.

Learning the names of the Stars, 287.

Leibnitz mountains, 131.

Le Mairean or Herschelian telescope, 13.

Lenses, Cleaning, 59.

—— out of centre, 55.

Leonids, 276.

Lescarbault rediscovers Saturn, 350.

Le Verrier, Theoretical discoverer of Neptune, 222.

Lick, James, Founder of the Lick Observatory, 18.

Lick refractor, Performance of the, 27.

Light of Comets, Fluctuating, 245.

Limited means no obstacle, 51.

Lippersheim, Hans, Inventor of the telescope, 4, 5.

Lunar changes, 120.

—— formations, 123.

Lyræ α, 308.

Lyrids, 275.

Mädler’s observations of Lunar objects, 127, 131.

—— —— of Mars, 158.

—— —— of Venus, 149.

Magellanic clouds, 331.

Magnitudes of Stars, 294.

Marius, Simon, observes Jupiter’s satellites, 6.

—— observes Nebula in Andromeda, 326.

Markings on Mercury, Surface-, 142.

—— on Venus, 147.

—— ——, Faintness of, 150.

MARS, Appearance of, 155. Period &c., 155. Phase, 156. Surface-configuration, 156. Charts and nomenclature, 158. Discovery of satellites and canal-shaped markings, 159. Summary of observations, 160. Rotation, 161. Further observations required, 162. Changes on the Planet, 163. Satellites, 164. Occultations by the Moon, 166.

Martin’s 4-foot reflector at Paris, 15; Its performance, 25.

—— 29-inch refractor at Paris, 18.

Maunder on Sun-spots, 93.

Maxima and minima of Sun-spots, 100.

Means of measurement, 290.

MERCURY, 137. Supposed planet Vulcan, 137. Visibility, 138. Period &c., 138. Elongations, 138. Amateur’s first view, 139. Phases, 139. Atmosphere, 139. Telescopic observations, 140. Schiaparelli’s results, 141. Observations of Schröter and W. Herschel, 142. Surface-markings, 142. Transits across the Sun, 143. Occultations, 144.

Messier, The Comet-hunter, 249.

Messier’s lists of Nebulæ, 327.

—— large Comet of 1769, 232.

METEORS AND METEORIC OBSERVATIONS, 260. Ancient ideas, 260. Meteoric apparitions, 261. Radiation of Meteors, 262. Identity of Meteors and Comets, 262. Aerolites, 264. Fireballs, 267. Heights of Fireballs, 268. Meteorite from Biela’s Comet, 270. Differences of motion, 271. Nomenclature of Meteor-systems, 271. Meteor-storms, 271. Telescopic Meteors, 272. Meteor-showers, 274. Varieties of Meteors, 276. Meteor of Dec. 28, 1888, 277. Average heights of Meteors, 277. Computation of Meteor-heights, 278. Meteoric observations, 279. Meteors and terrestrial objects, 284. —— and gales of wind, 285.

Method, 78.

Milky Way or Galaxy, 2, 295.

Minimum of Sun-spots, 347.

Mirrors, Dewing of, 62.

MOON, Attractive aspect of the, 113. Diameter and distance, 114. Crateriform aspect, 114. Absence of air and water, 115. Only one hemisphere visible, 115. Earthshine, 116. Telescopic observations, 116. Eclipses, 118. Physical changes, 120. Active volcanoes, 120. Crater Aristarchus, 120. —— Linné, 121. —— near Hyginus, 122. General description of formations, 123. Description of special objects, 125-132. Objects near terminator, 133. Occultation of Stars, 135. Visibility of new and old Moon, 136.

Moonlight and planetary definition, 187.

Motion of light, 190.

Motion of Stars in the line of sight, 300.

—— of Sun-spots, Proper, 106.

Mounting of Telescopes, 45.

Naked-eye views of Comets, 248.

—— —— of Jupiter in daylight, 170.

—— —— of Jupiter’s satellites, 188.

—— —— of Mercury, 139.

—— —— of Sun-spots, 89.

—— —— of Uranus, 217.

—— —— of Venus in transit, 105.

—— —— of Vesta, 168.

Names of the Stars, Learning the, 287.

Nasmyth and Carpenter describe Plato, 126.

Nasmyth’s Telescopes, 16.

—— “Willow-leaves,” 101.

Nature of Cometary apparitions, 229.

—— of the red spot on Jupiter, 177.

NEBULÆ AND CLUSTERS OF STARS, 324. Distinction, 324. Large number visible, 324. Varieties of form and grouping, 325. Distribution in R.A., 326. Early observations, 326. Variable Nebulæ, 327. Nebulous Stars, 330. The Magellanic Clouds, 331. Double Nebulæ, 332. Real dimensions of Nebulæ and Clusters, 332. Round Nebulæ and Clusters, 332. Description of Nebulæ and Clusters, 333. Great Nebula in Andromeda, 334. —— —— in Orion, 334. Planetary Nebulæ, 334. Spiral Nebula, 335. Crab Nebula in Taurus, 336. Dumb-bell Nebula, 337. Ring Nebula in Lyra, 337. Elliptical Nebulæ, 338. Globular Clusters, 338. Further observations, 339. Discovery of new Nebulæ, 341. New Nebulæ discovered at Bristol, 342. List of Clusters of Stars, 343. —— of globular Clusters, 344. —— of Nebulæ, 345.

Nebulous Stars, 330.

Neison, Lunar observations, 128, 129.

NEPTUNE, Discovery of, 221. Observations in 1795, 222. Period &c., 223. Observations, 223. Supposed ring, 223. The satellite, 223.

New or temporary Stars, 312.

Newton, 128.

Newton, Sir Isaac, Experiments on Colours, 9.

——, His reflecting-telescope, 11.

——, On mountainous sites for telescopes, 347.

Noble, Occultation of Jupiter, 186.

——, Occultation of Saturn, 210.

—— on observations of Mercury and Venus, 348.

Nomenclature of Comets, 246.

—— of Lunar formations, 123.

—— of Mars, 158.

—— of Meteor-systems, 271.

Number of Comets visible, Large, 228.

—— of Nebulæ and Star-clusters, 324.

—— of Planetoids, 167.

—— of Stars, 293.

Observations of Neptune, 223.

—— required of the Sun, 97.

—— —— of the Moon, 116.

—— —— of Mercury, 143.

—— —— of Venus, 152.

—— —— of Mars, 162.

—— —— of Jupiter, 183.

—— —— of Saturn, 205.

—— —— of Uranus, 219.

—— —— of Comets, 243.

—— —— of Meteors, 279.

—— —— of Stars, 320.

—— —— of Nebulæ, 339.

——, Solar, 88.

Observatories, 64.

Observer’s aims, 42.

Observing, Open-air, 75.

Observing-seats, 53.

Occultations of Jupiter, 185.

—— of Jupiter’s satellites, 189, 190.

—— of Mars, 166.

—— of Mercury, 144.

—— of Regulus by Venus, 154.

—— of Saturn, 209.

—— of Star by Jupiter, 193.

—— of Venus, 153.

—— of Vesta, 169.

Olbers discovers Pallas and Vesta, 167.

——, His Comet of 1815, 235, 241.

——, Observer of Comets, 250.

Open-air observing, 75.

Opera-glass, 61.

Orbits of Comets, Differences in, 230.

Orion, Great Nebula in, 334.

——, The constellation, 289.

Orionids, 275.

Orionis β, 307.

—— θ, 318.

—— σ, 318.

Outbursts of Faculæ, 108.

Palisa, Discoverer of Planetoids, 167.

Palitzch, Discoverer of Halley’s Comet, 236.

Pallas, 168.

Parabola, 230.

Past and future work, 84.

Periodical Comets, 234.

—— ——, Grouping of, 241.

Periodicity of Jupiter’s markings, 184.

—— of Sun-spots, 100.

Perrotin observes the belts on Uranus, 218.

—— —— the canals on Mars, 27, 160.

—— on work with a 30-inch refractor, 347.

Perry on drawing Sun-spots, 93.

—— observes veiled Sun-spots, 110.

Persei β (Algol), 310.

—— χ, 317.

Perseids, 275.

——, Their shifting radiant-point, 283.

Perseverance, 79.

Petavius, 128.

Peters, Discoverer of Planetoids, 167.

Phase, Epochs of similar, 117.

—— of Jupiter, 172.

—— of Mars, 156.

Phases of Mercury, 139.

—— of Venus, 147.

Phobos, Inner Satellite of Mars, 165.

Photography, 82.

Photometric measures of Starlight, 295.

Physical aspects of Comets, 244.

—— changes on the Moon, 120.

Pickering on the canals of Mars, 348.

Planetary bodies on the Sun, 105.

—— conjunctions, 225.

—— Nebula, 334.

Planetoid, The 308th, 349.

PLANETOIDS, Number of, 167. History of their discovery, 167. Occultation of Vesta, 167. Dimensions and brightness, 168.

Plato, 125.

Polaris, 308.

Pons, Discoverer of many Comets, 250.

Pons’s Comet of 1812, 241, 242, 245.

Pons-Winnecke’s Comet, 240.

Powers, Method of determining, 49.

——, Overstating, 49.

——, Requisite magnifying, 48.

Præsepe, 317.

Preparation of the observer, 66.

Princeton refractor, Performance of, 26.

Prizes for Cometary discoveries, 258.

Proctor on Amateur observers, 163.

—— on Sun-ejected Meteors, 349.

Projection of satellites of Jupiter, 190.

—— of Stars on the Moon, 135.

Prominences, Solar, 111.

Proper motion of spots on Jupiter, 173.

—— —— of Stars, 299.

—— —— of Sun-spots, 106.

Publications, Astronomical, 83.

Pulkowa, The 30-inch refractor at, 27.

Quadrantids, 274.

Radiation of Meteors, 262.

Ramsden’s positive eyepiece, 47.

Ranyard, Absorption of light by object-glasses, 37.

Recording Meteor-tracks, 280.

Records, 72.

Recurrent disturbances on the Sun, 110.

—— forms on the Sun, 111.

Red spot on Jupiter, Appearance of, 173; Rotation of, 175; Nature of, 177.

Refracting-lenses or burning-glasses, 3.

Refracting-telescope, 12.

Refractors and Reflectors, 39.

Rheita, Valley near, 131.

Rigel, 307.

Ring nebula in Lyra, 337.

—— of Neptune, Supposed, 223.

—— of Saturn, Division in the outer, 201.

—— ——, The Crape, 202.

Rings of Saturn, 201.

—— ——, Aspect of the, 204.

—— ——, Eccentric position of the, 204.

—— ——, Thickness, 205.

Roberts’s photographs of the Nebula in Andromeda, 334, 351.

—— —— of Nebulæ in Ursa Major, 338.

Rosse, Lord, Large reflecting-telescopes, 14; Their performance, 21.

Rotation of Comets, Visible evidences of, 246.

—— of Jupiter, 176, 348.

—— of Mars, 161, 348.

—— of Mercury, 142.

—— of Saturn, 199.

—— of the Sun, 103.

—— of Uranus, 217.

—— of Venus, 149.

Round Nebulæ and Clusters, 332.

Safarik on Telescopic Meteors, 273.

Saros, The, 99.

Satellite of Neptune, 223.

—— of Venus, Alleged, 152.

Satellites of Jupiter, 187.

—— of Mars, 164.

—— of Saturn, 211.

—— of Uranus, 220.

SATURN, 195. Apparent lustre, 195. Period &c., 196. “Square-shouldered” aspect, 196. Early observations, 197. His belts and spots, 199. Rotation-period, 199. The Rings, 201. Divisions in outer ring, 201. Crape-ring, 202. Discordant observations, 204. Eccentric position of rings, 204. Aspect of the rings, 204. Further observations, 205. Occultations of Saturn, 209. The Satellites, 211. Transits of shadow of Titan, 213. Occultations of Stars by Saturn, 214.

Scheiner’s early observations of Sun-spots, 89.

Schiaparelli, Observations of Mars, 159.

——, Observations of Mercury, 141.

—— associates Comets and Meteors, 264.

Schmidt announces change in a lunar crater, 121.

——, Discoverer of a new Star, 315.

Schröter’s observations of Mercury, 142.

—— —— of Saturn, 200.

—— —— of Venus, 148.

Scintillation of Stars, 297.

Scorpii α, 309.

Shadows cast by Faculæ, 109.

Short’s reflectors, 12.

Showers of Meteors, 274.

Sidereal work, 286.

Silver-on-glass films, Duration of, 60.

Sirius, 300, 307.

Small telescopes, 31.

—— —— and Mars, 160.

—— —— and Solar work, 90.

Solar Eclipse of Aug. 19, 1887, 98.

—— Eclipses visible in England, 98.

—— observations, 88.

—— Prominences, 111.

Southern Comets, Large, 233, 234.

Spiral Nebula, 335.

Spitaler’s Comet of 1890, 349.

“Square-shouldered” aspect of Saturn, 196.

Star-disks, 298.

Stars, Nebulous, 330.

——, Occultation of, 135.

—— visible through Comets, 246.

STARS, THE, 286. Sidereal work, 286. Greek Alphabet, 287. Learning the names of the Stars, 287. The constellation Orion, 289. The constellation Figures, 290. Means of Measurement, 290. Dividing power, 292. Number of Stars, 293. Magnitudes, 294. The Milky Way, 295. Scintillation of Stars, 297. Star-disks, 298. Distance of the Stars, 299. Proper motions of Stars, 299. Double Stars and binary systems, 300. List of Double Stars, 302-5. α Canis Majoris, 307. β Orionis, 307. α Lyræ, 308. α Ursæ Minoris, 308. α Scorpii, 309. Variable Stars, 309. ο Ceti and β Persei, 310. List of Variable Stars, 311. New or temporary Stars, 312. Description of temporary Stars, 312. Star-colours, 315. Groups of Stars, 316. Coma Berenices, 317. The Pleiades, 317. Præsepe, 317. χ Persei, 317. κ Crucis, 318. ζ Ursæ Majoris, 318. σ Orionis, 318. θ Orionis, 318. Further Observations, 320.

“Stops,” Utility of, 58.

Storms, Meteor, 271.

Straight Wall, 130, 131.

Streak seen at Jask, Meteor-, 278.

Structure of Sun-spots, Crateriform, 101.

SUN, THE: Diameter and Distance, 87. Solar observations, 88. Spots on the Sun, 88. Early observations, 88. Small telescopes and solar work, 90. Tinted glass, 91. Solar diagonal, 92. Drawing Sun-spots, 93. Ascertaining dimensions, 94. Sun-spot of June 19, 1889, 95. Eclipses of the Sun, 97. Periodicity of Spots, 100. Crateriform Structure, 101. “Willow Leaves,” 101. Rotation of the Sun, 103. Determining the Period, 104. Planetary bodies in transit, 105. Proper motion of Sun-spots, 106. Rise and decay of spots, 106. Black nuclei in the Umbræ, 106. Bright objects near Sun, 107. Cyclonic Action, 108. Sudden outbursts of Faculæ, 108. Shadows cast by Faculæ, 109. Veiled Spots, 110. Recurrent disturbances, 110. Recurrent forms, 111. Exceptional position of Spots, 111. The Solar prominences, 111.

Sun-spots, 88, 347.

Superstitious ideas on Comets, 227.

Surface configuration of Mars, 156.

—— markings on Mercury, 142.

—— —— on Venus, 147.

Sweeping for Comets, 249.

—— for Nebulæ, 340.

Swift, Discoverer of Comets, 252.

——, —— of Nebulæ, 339.

Tails of Comets, 244.

Tarrant on Double Stars, 291.

Telescope, Invention and Development, 1.

Telescopes, Cheapness and increasing number of, 57.

——, Choice of, 38.

——, Large and small, 20.

——, Mounting of, 45.

——, Testing, 43.

Telescopic Comets, 256.

—— Meteors, 272.

—— Work, Attractions of, 85.

Tempel’s Comets, 241.

—— Nebula in the Pleiades, 329.

—— observation of Aristarchus, 120.

Temporary Stars, 312.

Tenuity of Comets, 229.

Terby’s White Spot on Saturn’s rings, 203.

Terminator, Moon’s age and Objects near, 133.

Testing Telescopes, 43.

Test-objects, 55.

Theophilus, 128.

Thornthwaite, Method of Solar observation, 92.

Tinted glass for Solar observation, 91.

Titan, Transit of, 213.

Total Eclipses of the Moon, 118.

—— —— of the Sun, 99.

Transits of Intra-Mercurial Planets, 105, 137.

—— of Jupiter’s satellites and their shadows, 189, 191.

—— of Mercury, 143.

—— of Venus, 153.

Trans-Neptunian planet, 224.

Tupman, Method of tabulating Meteors, 282.

——, Remarks on a Fireball, 267.

Tuttle’s Comet, 241.

Twilight on Venus, 151.

Twinkling of the Stars, 297.

Tycho, 127.

URANUS, Discovery, 215. Mistaken for a Comet, 215. True character revealed, 216. Period &c., 217. Observations, 217. His belts, 218. Further observations, 219. The satellites, 220.

Ursæ Majoris ζ, 318.

Ursæ Minoris α, 308.

Utility of “stops,” 58.

Variable Nebulæ, 327, 351.

—— Stars, 309.

—— ——, List of, 311.

—— ——, Observations of, 321.

Variations in the light of Comets, 245.

Varieties of form and grouping in Nebulæ and Star-clusters, 325.

—— of Meteors, 276.

Vega, 301, 308.

Veiled Sun-spots, 110.

VENUS, Beauty and brilliancy of, 145. Period &c., 146. As a telescopic object, 146. Surface-markings, 147. Rotation-period, 149. Faintness of the markings, 150. Twilight, 151. Alleged satellite, 152. Further observations, 152. Transits, 153. Occultations, 153.

Vesta, 168; Occultation of, 169.

Visibility of Mercury, 138.

Vision, 70.

Vulcan, Supposed planet, 137, 348.

Wargentin describes a Lunar Eclipse, 119.

Warner’s Comet-Prizes, 259.

Washington Refractor, The great, 25, 36.

Weather and Comet-seeking, English, 251.

Webb, Lunar observations, 127, 130, 131.

——, Markings on Mercury, 143.

Williams, Observations of canals of Mars, 160.

——, —— of Jupiter, 175, 177.

——, —— of Jupiter’s satellites, 191.

——, —— of Plato, 126.

“Willow-Leaves,” The Solar, 101.

Wind, Its influence on definition, 69.

With of Hereford, Maker of glass specula, 15.

Wolf on large and small Telescopes, 25, 35.

Working-lists, 68.

Young, Performance of 23-inch refractor, 26.

—— observes belts on Uranus, 217.

—— on the successes of small instruments, 34.

PRINTED BY TAYLOR AND FRANCIS,

RED LION COURT, FLEET STREET.