Observations of the Southern Nebulae made with the Great Melbourne Telescope from 1869 to 1885. Part I. Melbourne.

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Frontispiece (photo) untitled, showing the observatory, telescope, and grounds.

Title page

"Preface"

"Introduction" (page 1 … 7)

illustration (sketch): "Plan of the Great Telescope House"

illustration (photo) untitled, showing the telescope

"Observations of the Southern Nebula …" (page 9 … 25)

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Observations of the Southern Nebulae / made with the / Great Melbourne Telescope / from 1869 to 1885 / Part I.

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Untitled photograph, showing the observatory, telescope, and grounds.

Observations of the Southern Nebulae / made with the / Great Melbourne Telescope / from 1869 to 1885 / Part I. / Under the direction of / Robert L. J. Ellery, F.R.S., F.R.A.S., etc. / Government Astronomer. / [Royal Coat of Arms of the United Kingdom] / By authority: John Ferres, Government Printer, Melbourne. / 1885

Preface

The Great Melbourne Reflector, since its erection in 1869, has been devoted chiefly to a revision of the Southern Nebulae observed by Sir John Herschel at the Cape of Good Hope in the years 1834 to 1838. Unavoidable delay has occurred in the publication of the results of these observations; but it is now intended to issue the drawings, descriptions, observer's notes, &c., in parts.

The first part contains a brief description of the Telescope, its characteristics and its performance, and an explanation of the modes of observation and drawing, as well as descriptions and lithographs of a number of the smaller Southern Nebulae.

Other parts, containing the results of observations for the revision of Southern Nebulae up to the end of 1884, will be published at as short intervals as possible.

Introduction

The four-foot Cassegrainian Equatorial, now known as the Great Melbourne Telescope, was erected in June 1869, and the observations, the results of which are given in the following pages, commenced in August of the same year.

This instrument was constructed by the late Thomas Grubb, of Dublin, and an admirable description of it, illustrated in every detail from the pen of the late Dr. T. Romney Robinson, D.D., F.R.S., of Armagh, appears in the Philosophical Transactions of the Royal Society of London, 1869, page 127. It will therefore be sufficient to give here a brief general description only, assisted by reference to the Frontispiece, which shows the Telescope in position.

The following are the principal dimensions :—

The equatorial mounting of the Telescope is of a form somewhat similar to the Sisson, the declination axis being placed between the upper and lower pivots of the polar axis, which run in large bearings, supported by two distinct massive stone pillars rising from a solid bed of masonry. The R.A. circle, clamps, and slow motion apparatus are between the declination axis and lower pivot. The declination circle is fixed to the bearings of the declination axis on the side of the polar axis opposite to the Telescope.

There are two large mirrors, each mounted ready for attachment to the Telescope, in its cell or box, and floating on its complicated supports of forty-eight cups and balls attached to the ends of the arms of a series of triangular levers, and upon hanging rings around its circumference. For the detailed description of this mode of supporting the mirrors the reader is referred to Dr. Robinson's paper, already mentioned.

These mirrors are perforated by an opening in the centre of eight inches diameter to admit the passage of the cone of rays from the convex secondary to the eye-piece.

There are two small metal mirrors, and there was also a glass combination (for silvered surface reflection) supplied; but it unfortunately got broken, and the first two have been the only ones used.

The tube of the Telescope consists of three portions. The lower or "eye end" portion consists of the box carrying the large speculum; the central part is a cylinder of boiler plate about 93 inches long, to which is attached the declination axis by means of a massive cast-iron cradle and strong iron bands embracing the cylinder. The speculum box fits to this cylinder on turned surfaces, and is held to it by three strong screw-bolts. The remainder of the tube is made of open steel lattice-work, about 20½ feet long, and fixed by turned flanges to the boiler-plate cylinder by bolts and nuts.

It is so arranged that the large speculum is only about 45 inches below the centre of the declination axis, while the object end of tube is about 22 feet above it. This limits most conveniently the motion of the eye-piece within a comparatively small range.

[running header: 2 INTRODUCTION]

The small mirror in its cell or box is mounted on the lattice tube about 300 inches from the surface of the large speculum and 39 inches within the object end of the tube and 60 inches within the primary focus of the large mirror, which lies 21 inches beyond the outer end of the lattice tube. It is carried by a bracket or arm of flat steel tube rigidly fixed to a sole-plate bolted to the lattice tube. This arm carries a strong gun-metal slide-rest, to which the mirror cell is attached, having its motion in the direction of the optical axis. By this means a motion of the mirror to or from the eye along the optical axis of the Telescope is readily obtained with an endless cord, which passes round a pulley at the end of the slide-rest screw, and thence by guide-pulleys to a large annular pulley with hand-wheel surrounding the eye-piece cell.

The polar axis, 123 inches long, has pivots 12 inches diameter. The R.A. circles consist of one fast and one loose circle, with two verniers to each to permit of setting to right ascensions. There are quick and slow motions for the polar axis. The declination axis is 22 inches diameter at the bearing next the Telescope and 9.5 inches at the counterpoise end.

There are quick and slow motions in declination, the manipulation of which from the eye end is very convenient.

The driving block is itself a large machine, governed by a double conical pendulum of the well known "Grubb" form. The direct driving weight is 260 lbs.

The total weight of the moving parts is about 18,000 lbs.; nevertheless the instrument is so beautifully counterpoised and so skilfully relieved of friction in all its bearings that it can be traversed from one side of the pier to the other, and set on an object in less than a minute by one man as readily as a much smaller instrument.

Accessories — The Telescope is provided with a finder of 4 inches aperture, seven negative eye-pieces, a filar-position micrometer, a spectroscope, two photographic cameras, and a number of plate-holders. The eye-pieces are all negative or Huygenian, with powers varying from 234 to 1000.

The micrometer is of somewhat peculiar construction, consisting of a large negative eye-piece with the wires in the focus of the eye-lens, alteration of the power of the micrometer being obtained by using different eye-lenses. There are two micrometer screws, as in the ordinary English form of parallel-wire micrometer. Besides the usual webs or wire, there are two metal bands attached to the screw slides, which are useful for measuring very faint objects on a dark sky without any illumination of the micrometer. The value of a revolution of the screw in this form of micrometer varies with the distance the respective bisecting web is from the centre of the field, one revolution at the centre of the field = 10′′.84, and on the edge of the field = 8′′.90, with a power of 207. A table of values is given further on. There are three eye-pieces, whose magnifying powers are 207, 315, and 452 respectively.

The Spectroscope is fully described in Dr. Robinson's paper. It consists of an adapter, which fits to the telescope in the same way as the eye-pieces, into which is screwed the prism box, with collimator and telescope attached.

Both collimator and telescope have objectives of 1.1 inch aperture and 4.5 inches focal length.

In the adapting tube are openings for adjustment of slit, position and focus, and also an arrangement for spark-spectra for comparison, as well as a reflector to assist in bringing stars accurately on the slit.

For the purpose of measurement, the small Telescope is movable about the centre of the prism box by means of a micrometer screw moving on the racked edge of a small fixed sector. Either a single prism or one of two compound prisms of different dispersive powers can be fitted into the prism box.

The cameras, when used, are attached to the extreme end of the lattice tube, where the plate-holder is just about 30 feet from the large mirror (the small mirror, of course, being removed whenever the Telescope is used for photographic work). There are complete arrangements for focussing the plates from the eye as well as from the object end, and a special shutter for

graduating the exposure in lunar photography. The plate-holders for the two cameras carry glasses 6′′ x 6′′ and 5′′ x 6′′ respectively.

For repolishing the mirrors, and for removing or changing them, there were furnished with the Telescope a small steam engine, two polishing machines, a crane, a mirror carriage, polishing tools, &c.

Building. — The building in which the Telescope is housed, shown in plan (Lithogr.), consists of a rectangular structure, 84 feet long North and South, and 28.3 feet wide, with walls 8.5 feet high, divided into two by a party-wall.

The northern half of the building, in which the Telescope is mounted, is covered by an iron gable-shaped roof, which is movable on iron rails fixed along the whole length of the East and West walls of the building.

The southern half of the building is divided into three chambers, and is covered by a low, flat roof of zinc, over which the gable roof of the Telescope-house runs free. These chambers are respectively engine and polishing room, work room, and observer's room at the south end of the building. The furnace and boiler room forms a small wing to the polishing room, as seen on plan.

The roof of the telescope room is an ingenious structure of angle iron covered with corrugated iron roofing; and as the south polar pivot and its pier stand higher than the walls upon which the roof travels, the northern gable-end wall frame is cut away to allow it to pass over these parts of the instrument and piers. In order to avoid any opening out of the roof frame from this condition, very careful trussing and bracing of the frame of the roof was necessary, and this has been so successfully carried out that no alteration of the shape of the structure is perceptible after fourteen years use.

The movable roof weighs nearly ten tons and rests upon eight small railway wheels. For moving it off or on there is provided at the centre of the southern end of the roof a small stage with winch and pinion, working into a large toothed wheel on an iron shaft the whole width of the roof; this shaft has at each end a pinion engaging into toothed wheels fixed to the two southernmost rail wheels. By turning the winch, the roof can be moved by one man steadily and easily on or off the telescope room.

The portion of the north gable cut away as already mentioned is provided with doors, which, before removing the roof, are swung so as to leave a clear space for passing over the Telescope and piers. When the roof is removed for observing, the whole sky is exposed to view with the exception of a portion below the south pole intercepted by the roof resting over the southern half of the building. There are anchors and chains on each side to prevent the roof moving from pressure of wind when on or off the Telescope.

The height of the walls with respect to the intersection of the axes of the Telescope is such that when the tube rests on the walls in the meridian it has an elevation of 15 degrees. When not in use, the Telescope is lowered almost to a horizontal position in the meridian on the east side of the pier, the tube resting on top of the photographic room, in which position it must be placed before the roof can pass over it either in running on or off. The photographic rooms occupy the S.E. corner of the telescope room, as can be seen on the plan.

In the polishing room are placed the large and small polishing machines, a two-horse power engine for driving, and a screw crane for lifting the large mirrors on and off the machine.

Performance, &c.. — An instrument of the form and dimensions of the Great Melbourne Telescope, being in a measure unique, some account of its performance, its good qualities, powers and defects, and the practical difficulties encountered in its application to different classes of work, is desirable, and may be interesting to astronomers.

In the first place, as to its mechanical advantage and defects. It has already been stated that the weight of moving parts of the instrument is about nine tons; nevertheless the disposition and counterpoising of this weight, in connection with most elaborate and ingenious contrivances

for relieving pressure, friction, and avoidance of flexure in the two chief axes, result in the smoothest motion in all directions, and when under control of the driving clock it follows diurnal motion as smoothly and regularly as the best mounted telescopes of smaller dimensions.

The driving clock also is excellent, and its rate is very constant. As might be expected from the great weight and leverage, there is a frequent tendency to some looseness or slight play in parts of the driving mechanism and clamping gear, so that while observing, puffs of wind produce a sudden displacement of the object; and indeed, unless the adjustments to prevent this are constantly watched, this defect becomes troublesome. There is a point between this looseness and actual tightness of parts sufficient to stop the driving clock that must be obtained to get the requisite stability of the instrument. Sometimes this defect may arise from there being too much counterpoise or friction relief in the bearings.

As the instrument is not housed within a dome when in use, but is fully exposed between four low walls to all movements of air, it follows that no observing can be done in strong winds, owing to very considerable tremors in the tube. Although the tube is very rigid and requires as Dr. Robinson points out, a weight of 112 lbs. at the object end of tube with its 30 feet leverage to produce a flexure of {one-twohundredth} of an inch, nevertheless the practical horizontal flexure amounts to 0.27 inch. Of course this seriously alters the collimation of the mirrors, and it becomes necessary to correct it in all positions of more than 20 degrees zenith distance, which is however readily accomplished by means of the three primary screws of the system of supporting levers of the large mirror, whose square heads can be reached through openings in the mirror box; a slight turn with a key of one or other of these screws soon brings the collimation right, which can be seen by the improvement of the images. This adjustment can be easily made by the observer while his eye is at the eye-piece.

The immense equivalent focal length of the Telescope, namely 160 feet, itself introduces difficulties; the first, in the limitation of the field, which with the lowest eye-piece is only 12′ 30′′ diameter; the second, the impossibility of getting low-power eye-pieces without unwieldy lenses. The lowest Huygenian magnifies 240, and its field-lens is 9 inches diameter and about 1 inch in thickness. The large focal length also makes the use of the Spectroscope much more difficult than usual.

As in all instruments of large aperture, atmospheric condition is all important in the use of this one, and only those who have had experience in observing with such instruments can form an idea of how limited are the hours per year, even in a climate like that of this part of Australia, in which such large apertures show the full extent of their powers. On the average of ordinary fine nights, the performance of this telescope on a planet or a double star is disappointing — except perhaps in occasional glimpse — to one accustomed to observe with smaller apertures; but on really good nights it is quite different, and such occasions show the most delicate markings on Saturn, clear separation of discrete points in some of the resolvable nebulae, and a separation of close double stars, indication an optical perfection which under other conditions was not apparent. There is a want of blackness of field, when pointed to a dark sky, which is so desirable in some classes of work, especially in detecting the faintest objects, as if there was a little scattered light from the mirrors. A bright object in the field, though artificially eclipsed, fills it with too much light. This was especially manifest in our searches for Mars' Satellites in October 1877, and to this, no doubt, may be attributed the fact that they were not found earlier and more easily.

The number of nights fit for using the Telescope have been found to be about 40 per cent., but the best nights only 17 per cent., during the fifteen years the Telescope has been in use. Clear nights with high wind are reckoned bad nights, and so are moonlight nights for the special work to which the instrument has been chiefly devoted, namely, observation of nebulae and clusters. Many moonlight nights have been utilised for Lunar Photography, still they are reckoned as bad nights for other work.

Although the percentage of average observing nights, I think, is larger than in the Northern Hemisphere, evidence is in favour of the best nights in European and N. American Observatories being better that those in this part of Australia. The best nights have been found to be those where the barometer is about 30.0, falling, and the temperature slightly rising, nearly always in front of a moderate cyclonic movement of the atmosphere. It is on such nights, when the stars are without scintillation and look dull, that the Telescope develops its full power.

When employed for photography, the small mirror is removed, and the camera fixed on the object-end, as already described; for all photographs are obtained at the primary focus, and no attempt has been made yet to get pictures at the combined focus. The image formed by the large mirror on the photographic plate is exceedingly good, as can be seen by reference to the Moon pictures, which have already been distributed. The Moon's image at the primary focus is 3.5 inches. With the wet collodion process, which has been mostly used, the exposure necessary for a good picture is generally from one to three seconds. With the new rapid gelatine plates we can scarcely get the exposure short enough without reducing the aperture of the mirror.

Several photographs of star clusters and nebulae have been taken with gelatine plates, and for these the exposure required has been from one to six minutes. It has been found however that images of stars are enlarged if the exposure exceeds two minutes, and if there is any wind they are also elongated by vibration of the tube.

From numerous experiments made in the application of this instrument to celestial photography, the conclusions at present arrived at are, that at the primary focus, where exposures do not exceed a few seconds, magnificent results are obtained; but that longer exposures, owing to the difficulty of avoiding tremors and slight movements of the Telescope, do not give sufficient promise to warrant devoting much time to it; and, after all, except perhaps for the sake of experiment, it is not apparent that such photographs are at present likely to be of any value.

In photographing the nebula in Orion and that about {eta} Argus, the former gave a fair picture in two minutes, while the latter left no trace on the plate after an exposure of five minutes. The light of the latter object appears as bright as the former, and the fact stated can only be accounted for by supposing the chemical rays to be far more powerful in one than in the other.

The immense light-gathering power of this instrument offers great advantage in obtaining bright spectra of moderately faint objects, and the spectrum of a sixth magnitude star, showing the lines sharply and clearly, is a very bright one. Owing to the very long focus, there is, of course, considerable difficulty in keeping a star well on the slit, and it requires a quiet night and steady working of the instrument to do spectroscopic work comfortably or advantageously.

Observers — The first observer in charge of this Telescope was Mr. Albert Le Sueur, who was appointed while the Telescope was in course of construction at Dublin in 1866, and spent a considerable time in Mr. Grubb's workshop during the grinding and polishing of the mirrors and the trials of the instrument prior to being sent to its destination. He arrived in time to supervise its erection, and subsequently took charge of the observing until July 1870, when he resigned his position and returned to England.

Mr. A. Le Sueur was succeeded by Mr. E. Farie McGeorge, formerly of the Geodetic Survey of Victoria, who held the position until July 1872, when he also resigned. Mr. Joseph Turner was appointed to succeed Mr. McGeorge in February 1873, and remained in the position until his death in August 1883.

From that date till the present time Mr. Pietro Baracchi has held the position.

In the following pages the observers will be designated as follows:—

Modes of Observation and Drawing. — The modes of observing and drawing the nebulae and other celestial objects followed by the different observers were substantially the same, differing only in the manner of illuminating the drawing-board, or in its position. The eye-pieces generally used were No. 1, 2, or 3, whose powers are respectively 234, 280, and 330. In two of these eye-pieces reticles can be inserted and fitted to the stop between the two lenses in the focus of the eye-lens, and the wires so adjusted that one system lies parallel to the direction of diurnal motion and the other at right angles to it, the wires being sufficiently thick to be visible against an ordinary dark sky.

The form and dimensions of the reticles used are as follows:—

The sheets of paper used for sketching are ruled with faint lines to represent the reticle, the scale adopted being {three-eighths} inch = 1 minute of arc. The paper thus prepared is stretched and pinned to a light drawing-board, which is either fixed to an adjustable easel fitting on to the eye end, or placed on a table or in any position most convenient for the observer.

The eye-piece with reticle being attached, and the Telescope set upon the object with driving clock connected, drawing-board and lamp with shutter arranged, the observer proceeds to set the central intersection of the reticle upon some star, point, or condensation of a nebula to constitute the middle point of the picture, and then plots all the stars visible in the field, omitting however the very faint ones. This he does at first by eye alone, aided by the reticle; at the same time he estimates the magnitudes of the principal stars; after this he fills in the details of the nebula with "stumps" armed with plumbago of different grades.

To secure greater accuracy, the positions of stars involved in or close to the object, if brighter than the 13th magnitude, are generally roughly measured with the micrometer, or by transits over one or two wires of a reticle with declination wires closer than in the sketching eye-piece.

No drawing of a nebula or cluster was ever finished until it had been revised on at least one good night; for while there might be many nights sufficiently good for giving the general character, the more delicate details could only be obtained satisfactorily on the best nights.

The positions of the nebulae and clusters have been computed from those given in Herschel's Catalogue by simple application of the annual variation. &c. Herschel's places, as given in his General Catalogue (Philosophical Transactions of the Royal Society of London, Vol. 154, Part I.) were brought up to 1884.0, using his precessions for 1880, and when the places thus derived were found to agree with the present observed places within one minute of arc, they were adopted as correct; if not, new positions were obtained differentially with the nearest known star.

Reproduction of Drawings for Publication. — The best mode of economically and effectively reproducing for publication the numerous pencil drawings of nebulae, &c, made at this telescope has presented a difficult problem; and during a visit to Europe in 1875 I made numerous inquiries on the subject both in England and on the Continent. The most beautiful and satisfactory results were those produced from steel and copper plates; the expense of the processes was however very great. Photography in none of its methods seemed to offer any great promise, and it was ultimately decided to resort to lithography, and print the objects white on a black ground.

This has been done, but many difficulties presented themselves in the reproduction, and although the plates are as truthful and accurate representation of the drawings as the method

admits of, they are somewhat deficient in the fine gradation and finish one would hope for in drawings of these beautiful and delicate objects.*

A plan has lately been tried for reproducing these drawings by photography which promises well, and it is probable we may adopt it for future publication. The nebulae are drawn, not with pencil, but with dry white on dead black paper, and on as large a scale as convenient, the lights being stumped in with soft pads of cotton, or other material, and this drawing is then reduced to the required size by ordinary photography, and afterwards printed by any suitable process. The draughtsman has a larger surface to work on than by the old method, but this does not appear to offer any difficulty, and certainly working on a black surface keeps his eyes more sensitive than white, although more artificial light may be required in the former than in the latter case.

Arrangement of Published Observations. — As it has been decided to issue the Observations in parts, and is thought desirable that each object whose description and drawing is given should if possible be again observed and compared with the lithographs before publication, no particular order as to position of the object or as to catalogue number has been attempted, and the consecutive parts will generally contain descriptions and drawings of objects in the order in which they are now being revised, leaving the formation of a systematic catalogue for reference to a concluding part.

Each description is arranged as follows: 1st. - The number of the nebula or object in H.'s General Catalogue (Philisoph. Transactions, Vol. 154. Part I.); 2nd. - The number of same object in H.'s Results of Observations, Cape of Good Hope, in 1834-5-6-7-8; 3rd. - The number of plate and figure (if any) given by H. in the above work; 4th. - The dates (in years and decimals) of revisions at Melbourne, with initials of observers; 5th - Reference to Melbourne lithograph; and finally, the observer's notes and measurements, and comments by Editor.

For instance, the first description is of 67 General Catalogue, or 2327 Cape Catalogue, and where reference is made to Herschel's drawings, the plate and figure, say for Plate 6, Fig. 19, will be denoted thus:— (H.VI. 19).

The Melbourne lithographs in most instances contain figures of several nebulae on one plate; the plates are numbered as well as the figures, and will be referred to by symbol (M.IV.8), denoting Plate 4, Fig. 8.

In cases of new nebulae not described or figured in either of H.'s works, the number of Melbourne lithograph, if any, and position of object will precede description and notes.

The nebulae are drawn as seen in the Telescope, preceding being on the right and following on the left; North above, South below; each plate is marked with f and p on the left and right of the page, n on the top, and s on the bottom. They have been carefully drawn as regards position angle and distances and are all on the same scale, namely 1′ - 0.375 inch, or 8 minutes of arc = 3 inches on lithographs.

The lithograph figures, while generally very correct as regards outline, position. &c., are as a rule too hard and bright, for it was found almost impossible to imitate, even approximately, the fine gradations and filmy appearances of these objects; the faint luminosity which nearly always margins the more conspicuous portions, and which is shown in the original drawings, is lost in the lithograph, and, as a consequence the figures are not only more defined than in the drawings, but also smaller.

* The drawings on stone from the originals were done by Mr. E. R. Morris (an officer of the Mining Department, whose services were temporarily transferred for the purpose), at the Observatory, and under the immediate supervision of Mr. Turner, who was the observer in charge of the Great Telescope at the time. The printing and revisional work was carried out by lithographic staff of the Mining Department; and I must here acknowledge the valuable, cordial, and painstaking assistance received from Mr. Everett, Mr. Shepherd, and Mr. Finnie, members of that staff, and also the advice and assistance of the Government Printer, Mr. Ferres, in arranging the form. &c., of the publication.

Caption: PLAN OF THE GREAT TELESCOPE HOUSE

Caption: (none)

Shows observatory and telescope.

Observations of the Southern Nebulae made with the GREAT MELBOURNE TELESCOPE from 1869 to 1885

Description of Nebulae and Lithographs.

Nebula 67, 2327. H. VI. 19

Revised: L.S. 1870.08, T. 1875.84, B. 1883.84. Lithograph (M. I. I.) from drawing by T., November 1875.

L.S. observed and sketched this nebula 1870.08; sketch agrees with H. very closely; he remarks however referring to the two stars, one n.f. and the other s.f. centre of nebula:— "The position of these stars very different from H. (re-examine)." He gives position of longer axis of nebula 51° 39′′ but notes— "Hazy; not well seen." Distance of s.f. star 2′ 3′′. Magnitude of stars estimated = 12.

T., at the date of his drawing, notes:— "The present appearance of nebula is exactly as represented in H.'s sketch; the centre is sharp and stellar-like with power of 255; but with 420 it is more diffused, and somewhat sparkling. A careful examination leaves the impression that it is practically unchanged since H.'s time, the only difference between his sketch and present aspect being the position of the North star, which in H.'s sketch is shown in a straight line with the centre of nebula and s.f. star, whilst at present it is somewhat to the n.f. of that point; this may however be the fault of the engraver."

B. observed it 1883.84, and compared it carefully with the lithograph and notes by L.S. and T.; he remarks - "Drawing correct; notes by T. still apply."

In H.VI.19 the nebula is narrower than in the lithograph. The relative position of the stars and nebula are also different, as remarked by L.S.

In the sketches of both L.S. and T. the s.f. star is farther from the nebula than shown by H.

[running header: 10 DESCRIPTION OF NEBULAE]

B. again examined 1884.69, and notes as follows:—

Appearance of nebula the same as in H.'s time, and agrees exactly with T.'s drawings and the lithograph No. I."

Nebula 27, 2315. H.IV. 8.

Revised: T. 1875.83, B. 1883.73 and 1884.69. Lithograph (M. I. 2) from drawing by T., 29th October 1875.

T. remarks at the time of his drawing:— "The present appearance agrees well with H.'s description and drawing. The 'following' portion is now much fainter than shown by H.'s sketch; indeed it is so very faint that its exact outlines cannot with certainty be determined, a faint whitishness being all that can be made out, while the star-like appearance described by H. in his portion cannot now be seen. The 'preceding' portion is still, as shown by H., much the brightest. There are still three nuclei, the centre one of which is much the brightest. H. says this one appears to consist of stars; but although I have tried several powers, I cannot with any certainty, determine this point, although it has, at times, a sparkling appearance. The 'following' portion of this nebula appears to have become much fainter since H. observed it."

In the revision of September 1883, B. states:— "Following portion almost disappeared; all the rest agrees with above remarks and drawing; but night was bad, and must observe it again. I could only see a part of the preceding portion." And after a further examination in September 1884 he remarks:— "Appearance of nebula agrees generally with H.'s and T.'s drawing; the f. portion is very faint; the p. portion considerably bright; the central nucleus is surrounded by bright nebula on the n. side, as bright as any part of the nebula. T. places the central nucleus in comparatively faint nebula. Lithograph agrees exactly with T.'s original drawing."

Measures:— Central nucleus taken as the zero point.

Measures by T. in October 1875:— Central nucleus taken as 0 point.

Nebula 169, 2359. H.V.10.

Revised: T. 1875.96, B. 1884.76. Lithograph (M. I. 3) from drawing by T., December 1875. He remarks:— "The present aspect of nebula and position of stars agrees very fairly with H.'s sketch. There is a slight haze to-night, the day having been very hot. To see this object properly would require a perfectly clear sky; still, I feel convinced that my sketch represents very accurately its present aspect. There is not the least appearance or even suspicion of sparkling in the denser portions; it seems to be purely nebulous matter throughout. It is so faint that the eye has to be carefully protected from all extraneous light for some time before it can be distinctly seen."

B. notes in October 1884 as follows:— "Searched for it on two nights in September; could not see it. Observed it on 7th October 1884; flat, faint, nebulous patch, very large. Its contour cannot properly be traced; I have examined it for hours. It is different from H.'s and does not agree altogether with T.'s. The appearance of this nebula may be greatly altered by the state of the atmosphere; but an inspection of drawings shows some change, I think. The principal change is this, that the patch following does not exist at present, or it must be very much fainter than all the rest. Lithograph agrees with T.'s drawing."

Nebula 187, 2370. H. IV. 6

Revised: L.S. 1870.09, T. 1875.95, B. 1883.73 and 1884.70. Lithograph (M. I. 4) from drawing by T., December 1875. Another lithograph of this nebula from drawings by L.S. is given in (M. V11. 79).

T. remarks in 1875:— "It is very unlike H.'s drawing and description; indeed I cannot trace any resemblance between that and its present appearance; and were it not for its position, and the fact that L.S. observed and sketched it on 5th February 1870, I should be in great doubt as to its being the proper object. The position, however, accords with that given by H., and L.S.'s sketch is, in its general features, very like mine, so that there is no room for doubting its identity. The central portion is by far the brightest, being a cluster of stars so very distinct that they could almost be counted; and the nebula here also appears the most dense. From this point it proceeds s.f. for almost 1′ 30′′, terminating in a few very faint stars. Towards the n.p. direction it forms a complete bend or hook, and is here very faint. A little n.f. the main or central portion is a very small and faint round patch, which at times looks like a cluster of very faint stars, but I cannot with certainty determine whether or not it be stars or only nebula, although the night is an exquisite one, being clear and steady."

B. remarks in September 1884:— "Appearance of nebula unlike H.'s agrees with L.S.'s and T.'s drawings. Position of stars (relative), measured by transits, agrees with L.S. and T. pretty well. Small star near little round patch within the hook taken as zero point.

This nebula seems to have remained unchanged since L.S.'s observations 1870.09. The lithograph is exactly like T.'s original drawing; only the hook and n. branch much too bright; should be fainter than the rest."

Nebula 485, 2458.

No drawing by H. Revised: T. 1876.85, B. 1884.78. Lithograph (M. I. 5) from drawing by T., November 1876, who notes at that date:— "H.'s description is 'very faint, pretty small, very little elongated,' but I note 'small, faint, considerably elongated, brighter in middle, no appearance of resolvability.' The sky was very clear at the time this sketch was made. It shortly afterwards became hazy, and then the nebula appeared less elongated. The sky may have been hazy when H. observed it.

B. examined this nebula in October 1884, and remarks:— "Agrees exactly with H.'s; T. says very much elongated; it is only a small object, very narrow, and only about 30′′ long.

From a diagram made with the reticle (described in the Introduction) the following measures are obtained:—

Lithographs agrees with T.'s drawing."

Nebula 491.

No figure by H. Revised: T. 1876.86, B. 1884.78. Lithograph (M. I. 6) from drawing by T. in November 1876. He remarks:— "Agrees exactly with H.'s description."

B., in October 1884, states:— "Very faint, roundish; double star in it 17m, like H.'s. Lithograph agrees exactly with T.'s drawing."

Nebulae 495, 497, 498, and 499. G. Cat.

No figure by H. Revised T. 1876.84. B. 1884.478. Lithograph (M. I. 7) from drawing by T. in November 1876. He remarks:— "No. 495 is the 'preceding' nebula; the others follow in the order of R.A. H.'s description of 495 is 'faint, small, round'; T.'s very faint and elongated. H.'s description of 497 is 'faint, small, round';. T.'s faint, small, round, brighter in middle'. These two seem to join or run into each other. H.'s description of 498 is 'very faint, very small, round'; T.'s round, brighter in middle, somewhat sparkling at times, and is rather the brightest of the group. H's description of 499 is 'very faint, very small, round'; T.'s pretty faint, elongated and considerably larger and brighter than 495. The condition of the atmosphere affects the appearance of these very much. The early part of this evening was clear and fine, showing the several patches as above sketched; afterwards it got slightly hazy, and all the patches had then a round appearance, like nebulous stars. The atmosphere may have been rather hazy when H. observed these; so that there is no proof of any alteration since that time."

B. says:—"495. Small, faint, elongated, forming a wing attached to 497. 497. Round, small, gradually brighter middle; pretty faint, but brightest of the group. 498. Very faint, a little brighter middle, and at times sparkling, as if a star were in it; cannot see the star. This is the faintest of the group. 499. Faint, a little brighter middle, a little elongated; cannot well see the shape of it; just a little brighter than 498, but very little. A double star (11 mag. and 16 mag.); star 11 mag is 2′ 35′′ South of 497, and has the same R.A.

498 follows star 11 mag by 14^s, and is 121′′ North of it.

499 follows star 11 mag. by 19^s.5, and is 17′′ South of it.

The relative position of these objects and their appearances agree closely enough with H.'s to show that no change has taken place. They also agree with T.'s observations. Discrepancies in the descriptions, though in some cases quite striking, yet, considering the nature of the group, which would perhaps alter in appearance with the least change in the state of the atmosphere, they may be considered of no importance. H. calls the four objects all equally round, whereas T. and I find the first and the last a little elongated. It may be assumed with good reason, therefore, that these two viz. 495 and 498, are not round, but a little elongated. But we cannot say that these objects have changed, because they are so faint and small that the different state of the atmosphere may have caused them to appear round in H.'s telescope. Again, T. calls 498 the brightest of the group, and I call it the faintest; yet between the brightest and the faintest objects of this group there is so very little difference that the opposite meaning of the two descriptions of the same object has no marked significance.

The lithographed copy of this group is correct, or at lest it agrees with T's original drawing."

Nebula 567, 2487. H. VI. 14.

Revised: L.S. 1869.83 and 1870.06, T. 1875.91, and B. 1884.78 and 79. The lithograph (M. I. 8) is from a drawing by T. in November 1875.

H. says:— "Pretty bright, large, pretty suddenly brighter middle, 3′ long 2′ broad, either binuclear or more elongated on the n.f. side than on the opposite.". (Page 50 of Cape Observations.)

His drawing is given (H. VI. 14). On another occasion he says:— "Bright, large, pretty much elongated, very suddenly much brighter middle, 100′′ long 60′′ broad, unequally bright, and exhibiting an approach to binuclear form." (Page 59 of Cape Observations.)

L.S. observed this object on 31st October 1869 and 23rd January 1870. He made a drawing of it (shown in Plate Vll. Fig. 80). He states that the weather was unfavourable on both occasions. His description of the object is only:— "Bright nucleus; almost stellar at times," evidently leaving the rest to be explained by the drawing. He points out its unlikeness to H.'s sketch and description.

T., in November 1875, says:— "So very unlike H.'s drawing and description, that, were it not that its position, as determined by comparison star, agrees exactly with H.'s position, great uncertainty would be felt as to whether it could be the same object. L.S. also observed it on 31st October 1869 and 23rd January 1870. He has drawn it very like what I have shown, and also draws attention to the difference between his and H.'s sketch. To-night is very clear and fine, and although I have tried several powers, I cannot detect any sparkling appearance in the nucleus, its appearance, together with that of the entire nebula, being of a phosphorescent character; and the form of the curved and densest part can only be satisfactorily seen by looking a little to the one side whilst the attention is directed towards the nebula. After careful examination, I feel certain that there is at present no double appearance, or anything at all approaching a resemblance to H.'s drawing. It must surely have altered its form since H.'s time, as he observed it upon 23rd October 1835 and 1st November 1836, and upon both of these occasions he refers to its double or binuclear appearance. A great change must surely have taken place upon it since then."

B., in 1884, notes:— "I observed this nebula on 14th, 16th and 18th October 1884 and January 1885. The following are the remarks made at the times of observation. 14th October. - Hazy. Sparkling nucleus, almost stellar; surrounded by faint nebula elongated in a direction n.f. and s.p.; I see no binuclear shape. 16th October. - Hazy. Appearance much the same as described on 14th. 18th October. - Clear. Elongated; suddenly much brighter middle: nucleus not so stellar as on previous observations; otherwise much the same appearance as before. 16th January. - Perfect night. Suggesting the shape of the letter S, only very slightly curved; pretty bright; suddenly very much brighter middle, 1′ 50′′ long; fading away gradually towards the two ends; position 45° approximate; unlike H.'s, and unlike T.'s; very like L.S.'s; T. makes a large object of it, formed by an S of nearly equal density, enveloped in fainter nebula in the shape of a perfect oval; he shows no bright nucleus in the centre of S, and, on the other hand, neither L.S. nor I saw the oval-shaped nebulosity around this S. True, L.S. had bad weather; but my last night was a magnificent one. Lithograph agrees with T.'s drawing "

Nebula 960, 2696.

No figure by H. Revised: T. 1876.86, B. 1884.88 and 1884.96. The lithograph (M. III. 20) is from a drawing by T., November 1876.

T., in 1876, remarks:— H.'s description is 'pretty faint, pretty small, round, two stars attendant.' I find it rather faint, sometimes appears sparkling; this may however be caused by the presence of the three stars involved. After careful attention, I think that the sparkling appearance is due solely to the presence of the involved stars, the nebula having the usual appearance. The three involved stars are not mentioned by H., and had they existed as at present, he could not have failed to notice them as he observed this object upon two different occasions".

B., revising it on 19th November 1884, on a night that had been favourable but was getting slightly hazy at the time of observation, says:— "This nebula must have changed its position, because there are no stars in it now, as T. says, and a double star is on the edge of it, just out of it, which double or triple star is not shown or mentioned by T.; besides, the star s.f. is now nearer the nebula than it is in T.'s drawing. I have observed this nebula twice already. It is a faint object, a little elongated in a direction s.f. It has a double star close to the edge n.p. forming a sort of light tail to it. I see no stars in it. Must re-examine."

Again examining this nebula on the 18th December 1884, B. notes:— "The night became somewhat hazy on 19th November, and I placed the double star quite out of the nebula. To-night I see that some nebula, like a ring, envelopes the two stars. But the two stars are comparatively in a nearly dark ground, and as if enclosed in an ill-defined ring. The brighter or denser nebula is found at this end s.f, where it seems to agglomerate and form as it were an almost detached part of this object. This object may at first be taken for an oval-shaped nebula, denser at the end s.f., or becoming gradually less dense towards the n.p., with two or perhaps more stars in it, but two quite distinct and pretty bright.

"NOTE. - A bright star 10½ mag. follows nebula by 52^s, and is 4′ South of it. Another star 11 mag. follows by 56^s, and is 5′ 15′′ South. There are hundreds of stars in the field. Lithograph agrees with T.'s drawing."

Nebula 961, 2697.

No figure by H. Revised: T. 1876.86, B, 1885.11. Lithograph (M. III. 21) from drawing by T., November 1876. T. remarks at this time:— "H.'s description agrees exactly with the present aspect." He subsequently states:— " The lithographer has not been quite successful with this nebula, as it ought to have a soft nebulous appearance, rather brighter in the middle and softening off gradually towards the edges."

B. notes on 10th February 1885:— "Small, round, bright, about 20′′; edge rather ill-defined, not sharp; sparkling at times; may be a little cluster, but could not make certain with any power. Agrees with H.'s position; also with T.'s drawing.

Nebula 962, 963, 966 and 968 = 2698, 2699, 2702, 2704.

Revised: T. 1876.86, B. 1884.86 and 1884.88. Lithograph from drawing by T., November 1876 (M. III. 22). For reference, these four nebulae are denoted by a, b, c, d, — a being 962, or the nebula most preceding in the figure.

T. remarks in November 1876:— " H.'s description of a (962) is 'very faint, small'; its present aspect is very faint and small, with three small stars, forming an equilateral triangle, involved.

H. does not mention these involved stars, and yet they are at present easily seen. H.'s description of b (963) is 'bright, round, resolvable'; its present form is as shown by lithograph, only much fainter, with five stars involved. H.'s description of c (966) is ' faint, small'; it is at present the largest of this group, being a group of very small stars involved in faint nebula. H.'s description of d (968) is 'pretty bright, very small, round'; at present it is a faint, round nebula, with a small star in centre, the nebula shading off very faintly at the edges. This is a most difficult group to identify, as it bears no resemblance to H.'s description, and but for its position, which has been several times verified, I should very much doubt whether these were the objects at all. There are no other nebulous patches near, and H. says these four form a sort of trapezium, so that these must be the objects sought; but they must have altered greatly since H.'s time, or else he must have observed them under very unfavourable circumstances. These patches of nebula are all so very faint that the slightest haze would suffice to obliterate them or change their appearance and shape. Indeed they are so very faint, and their outlines so uncertain, that I cannot make a drawing that can be much relied upon; and viewing them as contrasted with H.'s description, one would think they were being either absorbed or dissipated. This is, I think, the most unsatisfactory group I have yet fallen in with. Night very clear and fine."

On 19th November 1884 B. states:— "Observed on 13th, 18th and 19th November, the night of the 18th being beautifully clear. Observations of all these nights are quite concordant. This group is unlike H.'s and unlike T.'s. Referring to the lithograph, I find the positions of the four objects very different. a, the most preceding, is a group of minute stars surrounded by very thin nebula. b, is divided into two detached parts, the general direction of which is about 135°, and not nearly due N. and S. as shown in lithograph. The part preceding is faint, elongated {angle} 135°, about 30′′ long, brighter at the end p., with a star in it; diffused and fading into nothing at the end f. Then immediately after it, following generally the same direction {angle} 135°, comes an almost angular nucleus, formed by very minute stars, the vertex forming the preceding end of the object, then fades away towards the side s.f.; it is very small and considerably bright at the head. By the general direction stated above is meant a line passing through the angular point of the object just described and bisecting it, then produced through the elongated one, forming its long axis. If we imagine these two objects joined together, they would form nearly and elongated ellipse 20′′ broad and 50′′ long, dark in the centre, pretty bright at the end n.p., with a star in it near this end, much brighter and cluster like near the end s.f., and then fading away, leaving this end undefined and irregular. The centre of this ellipse follows a by only 7^s and is 60′′ South of it. d - Sparkling, stellar centre, considerably bright, small, like a diffused elongated star. This follows a by 26^s , and is 15′′ South of it. c follows d by 5^s, and is 90′′ North of it. Group of minute stars surrounded by nebula, very, very, very, faint; uncertain; impossible to draw its contour correctly. A flat, faint, round patch, without the least condensation, and agreeing exactly with H.'s follows d by 26^s, and is 3′ 10′′ South of it. It appears on the edge of the field (using sketching eye-piece), while the group gathers towards the opposite edge."

The great change, shown both in character and relative position of the components of this group, in the interval between T.'s drawing 1876.8 and B's observations in 1884.8 is somewhat remarkable. By reference to the lithograph, these nebulae come in the order of R.A. a, b, c, d; but B's measures show a and b now close together; b altogether altered in appearance; c in the lithograph precedes d, but B. now finds it following; and the character of d is also different to H.'s and T.'s description.

The lithograph agrees with T.'s drawing in 1876.

Nebula 964, 2692.

No figure by H. Revised: T. 1876.94; B. 1884.88. Lithograph (M. III. 23) from drawing by T., December 1876. At this time he remarks:— "H.'s description is 'very faint, very large, very much elongated, very gradually a very little brighter in middle, 4′ long and 2½′ broad.' Now it is so very faint as to be detected with great difficulty; the faintest trace of haze would render it totally invisible; and owing to its extreme faintness its exact outline cannot be with certainty traced. Its length at present is only about 2′ 20′′ and its breadth at broadest part about 40′ [sic], being much small than H. makes it."

B., in November 1884, says:— "Very, very faint; elongated, pointed towards n., almost to a minute star, which seems to form the n. end of it in a point. Has a star in it towards the end s. Much smaller and fainter than in H.'s time. Position of axis, 1° 30′. Length 2′, and 25′′ broad. Agrees with T.'s; seems unchanged since T.'s time". Agrees with lithograph, but star at n. apex more marked than shown.

Nebula 979, 2709

No figure by H. Revised: L.S., 1870.14; T. 1876.94; B. 1884.88. Lithograph (M. III. 24) from a drawing by T., December 1876. L.S. made a drawing of this nebula which agrees with H.'s description, and only notes "very faint." T. remarks:— "H.'s description agrees well with its present aspect; and the south patch of fig. 3, plate 3, of Cape Observations is meant for a representation of it. The drawing is however very inaccurate, and not at all like the object. L.S. made a drawing of this nebula on 23rd January 1870, which exactly corresponds with mine. Night clear and fine."

In 1882 T. remarks concerning the lithograph of this object:— "The lithographer has not been successful with this nebula. Its size and from are correctly shown; but it is really very faint, and has quite a soft appearance, and has three small stars of unequal magnitudes forming a triangle, involved."

B., in November 1884, says:— "Very faint, small, roundish, three stars in it, 16th or 17th magnitude. Agrees exactly with H. and T. No stars in the field. Three stars involved are not shown distinctly in the lithograph. They really appear as three distinct stars involved in very faint roundish nebula, whereas lithograph shows bright nebula with stars too diffused and uncertain."

Nebula 997, 2714

No figure by H. Revised: T. 1876.96; B. 1884.88. The lithograph (M. III. 25) is from a drawing by T., 19th December 1876.

T. says at date of drawing - "Present aspect agrees with H.'s description;" and in 1882 he says - "The nebula becomes gradually brighter towards the middle, not suddenly as shown in the lithograph."

B., on 20th November 1884, notes as follows: "Round, gradually brighter middle, almost to a point. Ill-defined contour, 20′′ or 30′′ diameter. Agrees with H. and T., and with lithograph."

Nebula 1021, 2740

No figure by H. Revised: T. 1876.96; B. 1884.93. The lithograph (M. III. 26) is from a drawing by T., 19th December 1876.

T. notes:— "The central portion appears at times as if it might be resolved; but I cannot see any distinct sparkling. Night very fine." In 1882 he says - "Lithograph represents very accurately its present appearance, which also agrees with H.'s description."

On 10th December 1884, B. remarks:— "Bright, very much elongated, suddenly much brighter middle, to a bright, sharp elongated nucleus, like a long dash. Nebula soft-edged. Fades away very gradually into pointed ends. Nucleus not quite in the axis of nebula. Appearance and position of this nebula agree with H. and T.; also with the lithograph.

Nebula 1057, 2775. (H. VI. 2.)

Revised: T. 1875.96; B. 1884.881. Lithograph (M. III. 27) from drawing by T., December 1875. T. notes at this time:— "It has a mottled appearance, the bright parts being very bright, as if consisting of very small stars. Sometimes these bright parts sparkle, but I cannot make out any distinct stars, although I feel convinced that these exist. The small star immediately south of nebula and close to it is involved in very faint nebula. H.'s drawing of this object is very unlike its present appearance. He describes it as having a double star in centre and his drawing also shows it so. The nebula presents altogether a more mottled appearance than indicated by H.'s sketch, and the two brighter parts might easily, upon an unfavourable night, be mistaken for the double star with H. shows in his drawing; I can however make nothing more of it than already stated. Night exquisite"

On 19th November 1884, B. notes:— "Pretty large, elongated, bright patches within it, not stars. Sparkling looks as if resolvable, but not so. Agrees exactly with T.'s drawing. Position of neighbouring stars agrees exactly with T. Nebula is most likely unchanged. H. puts a double star in it. This double star is perhaps represented now by the bright patches. It may be that H.'s stars have changed into diffused patches." Both T. and B. consider the lithograph as fairly representing the object.

Nebula 1096 and 1097 = 2806.

No figure by H. Revised: T. 1877.008; B. 1884.878. The lithograph (M. III. 28) is from a drawing by T., 4th January 1877. T. notes at this time:— "H. calls the preceding of these two nebulae round; it is at present elongated, as shown by drawing, and sparkles in centre at times, although no distinct stellar points can be seen. It might appear round on a hazy night. Night fine, and definition good." 1882.20:— "Lithograph agrees with present aspect."

On 18th November 1884, B. notes:— "Cannot see the two nebulae distinctly; I see only a faint elongated patch. Now quite hazy. Must re-examine." On 20th November he further notes:— "Much elongated, pointed, narrow. Little condensed at centre to a narrow ill-defined (not bright) sort of nucleus. Has a very small, very faint, round speck of a nebula near the centre. Night splendid. H. calls these two nebulae round and very bright; then they must have changed very much. My observations agree exactly with T.'s."

Nebulae 1156—63—64—74—76—77 = 2859—64— * * * *. (H. IV. 7.)

Revised: L.S. 1870.15; T. 1875.969; B. 1884.857. Lithograph (M. III. 29) from a drawing by T., 21st December 1875.

L.S. in 1870 remarks:— "Within the quadrilateral formed by this group many stars are easily discernible; also a general sparkling, and very, very faint nebula also suspected. The brightest nebula was specially examined with spectroscope; a faint continuous spectrum suspected; no line seen; very faint continuous spectrum over surface generally." He also notes:— "Nuclei of two smaller nebulae in s.f. group are stars."

T. in 1875, 21st December, states:— "This group is very difficult to identify, partly because the two n.p. patches are now much fainter than shown in H.'s sketch, and they do not now occupy the same position in relation to the s.p. patch. The most striking difference between H.'s sketch and present aspect however is that whilst in H.'s sketch the whole of the area embraced within the various patches (in shape somewhat resembling the Southern Cross) is filled with a regular and pretty easily distinguishable nebula, no nebula exists there now, the interior being quite free of nebulous matter. This space however presents a brightish appearance from the immense number of very small stars (might be call star-dust) crowded together in this region, and which upon a night not absolutely clear might be mistaken for nebula. L.S. made a sketch of this group on 26th February 1870, which corresponds exactly with mine, no interior nebula being shown. Night pretty clear and steady, but slightly hazy, after a hot day."

B. on 10th November 1884, notes:— "a. (1156) faintest of group, very faint and small, b. (1163) largest of group and second brightest; c. (1164) faint, small, only a little brighter than d. round; d. (1174) a little elongated, fainter than a, no condensation; e. (1176) is the brightest of group, round little brighter in middle; f (1177) pretty bright, not so bright as e, and much smaller, has a very little and faint patch n.p., hardly visible. Group agrees exactly with L.S.'s and T.'s drawing and description. There is now no nebula visible within the quadrilateral formed by this group, the components of which are only seen in a perfectly dark sky. The relative position at nebulae f, e, d is like H.'s; but the other three viz., a, b, c, are in a different position altogether from that shown by H.

Taking 1176 as the zero point, we have the following differential measures:—

Nebulae 1165—68—71—75 = 2866—67—68—69. (Group in Nubecula Major.) (H. VI. 20.)

Revised: T. 1875.972; B. 1884.854. Lithograph (M. III. 30) from drawing by T., December 1875. T. notes at this date:— "The several patches of this group are not at all so regular and well-defined as in H.'s sketch. The number of small stars here is very great, and their light almost hides the nebula. The three n.f. patches are so very thickly studded with very small stars that it is difficult to see any nebula at all, and except upon a very clear night none could be seen; at present the sky is very clear. The s.p. patch has no stars in it, and is very like as H. shows it — round, and gradually brighter in the middle. H.'s sketch shows only about a dozen stars, while at present the entire area embraced by the several patches is glittering with stars, mostly very small, with a few of about the 11th to 13th magnitude."

In 1882 he states:— "The lithograph represents pretty fairly the present appearance of the group, except that the second preceding patch is shown much too distinct and bright, it being in reality very faint and ill-defined."

B., in 1884, 9th November, notes:— "Night splendid. Agrees with T.'s description. This group must have changed position with regard to the brightest star in the group. In H.'s drawing this star is half-way between the two extreme nebulae f. and p., and almost in the centre of group; it is not so now. 1165 agrees now with H.'s. 1168 — It is hidden by the stars, looking almost like an irregular cluster. 1171 - It has stars in it, and I cannot say whether it is brighter in the middle. 1175 - Very irregular, small, indistinct, covered with stars. They all have an irregular, ill-defined shape, and are covered and surrounded with very small stars. 1165 is the best defined. Group agrees generally with H. and T.; seems to have undergone no change since H.'s time except in relative position. That star (a) is certainly not in the centre of group now, as H. placed it then. Agrees fairly with lithograph."

Position, 1884.00:—

Nebula 1267 = 368 of 1833 Catalogue = 78 Messier.

(H. Fig. 36, 1883 Catalogue.)

Revised: L.S. 1870.087: T. 1876.961; B. 1884.934. Lithograph (M. III. 31) from drawing by T., December 1876.

L.S. observed and sketched this nebula in 1870, but gave only the briefest notes of its appearance.

T., in December 1876, remarks:— "The present aspect agrees fairly with H.'s description as given in his Catalogue for 1833, viz., 'A very large wisp-shaped nebula, involving three stars.' In his General Catalogue, No. 1267, he says; 'It is very gradually much brighter to a nucleus.' This is surely a mistake. He also there says it is resolvable. I have tried it with several powers, but can detect no sparkling, or any other than the ordinary nebulous appearance. Night clear and fine."

In comparing the figures of H., L.S., and T. we find the outer contour much the same; but the inner or s.p. outline is different. H. shows the brightest or preceding star well involved in the densest nebula. The outline of the figure by H. may be taken as 'approximately round'; L.S. draws it somewhat of the same form, but refers to "a dark space hollowing out" the s.f. outline. T. draws it as shown in the lithograph, and in 1882 remarks - "The lithograph represents pretty fairly the present appearance of the nebula." The preceding arm is now much longer in a s.f. direction than shown by H. or L.S., and is the brightest part of the nebula.

B., observing this nebula in December 1884, notes as follows:— "Brightest on side n.p. This branch n.p. is quite distinct, and pretty sharp on the edges. The round turning n.f. is the faintest part; around central star nebula is very faint. The n.p. branch seems to begin from this star; the f. branch is just a little brighter near and about star south. In shape and position of stars it agrees exactly with lithograph, and fairly well with H.'s so I think the nebula has not changed. I do not see any sign of resolvability. T.'s remarks quite correct."

Nebulae 1248—49—58—59—60—65—66 = 2923—25—33—35—36—38—39.

(H.IV.9.)

Revised: L.S. 1870.096/161/233: T. 1876.318; B. 1884.964/975. The lithograph (M. IV. 32) is from a drawing by L.S., 7th February 1870, and the second lithograph (M. IV. 33) of the same group is from a drawing by T., 26th April 1876.

For reference, the nebulae in this group are designated in the order of R.A., using H.'s General Catalogue Number.

L.S. observed this group on three occasions in 1870. On the first he made a drawing and measured the relative positions of the seven objects, and remarked - "All the patches more or less condensed about the centre." On the second occasion he re-measured the positions and examined some of the objects with the spectroscope. His third examination of this group is also spectroscopic. He notes - " H. 1258, 1259, 1265 give no lines with certainty; with slit removed, the spectra of 1259 and 1265 are well seen, but it is difficult to say whether lines or not. A patch of light is seen spreading over a considerable space, say one-third of DG. Actual position not noted. With wide slit cannot see anything with certainty. H. 1259 is sufficiently bright,

if spectra were one of lines, to be seen easily; but this object and all those in group is so easily resolved that with high power the appearance is of an actual cluster.

The measures of the relative positions of the members of this group obtained by L.S., T., and B. are given together in the table below.

T., on the 26th April, notes:— "The general arrangement and appearance of the various patches are here much the same as shown by L.S., any difference being easily accounted for by possible different conditions of atmosphere. The principal difference between the two sketches is the shape of the south patch and its position in reference to the contiguous star. This is an exquisitely clear night; seen best with power 330, with which the background of the sky is seen 'powdered' with very minute stars. The several patches, when carefully examined, have all a decided sparkling appearance, leaving little doubt of their being clusters of apparently very small stars."

B., 18th December 1884, remarks:— "Made sketch of this group. Relative positions determined by transits, &c., using sketching eyepiece for differences of N.P.D. General character of group agrees with H., L.S., and T. There is an extremely faint, flat, a little elongated patch, not shown by any of the previous observers. It precedes H. 1260 by 14^s, and is 1′ North of it. Group now too near meridian. Night is becoming hazy. To be re-examined. 22nd December - Sketch made on 18th December correct.

The following table shows the differential measures of the different observers. H.'s were taken from the positions in General Catalogue. L.S.'s and T.'s differences of R.A. were obtained by transits and differences of declination by Grubb's micrometer:—

The above table shows that the relative position of the seven objects in this group seems to have remained nearly unchanged. Actually not one of the objects is exactly in the position given by H., but the differences are comparatively small, and are more likely caused by unavoidable error of observations than by real changes in the group.

In December 1884 B. further notes:—"The general appearance of the objects agrees with H., L.S., and T. pretty well, considering that different conditions of the atmosphere may affect these objects very much. In lithograph Fig. 32, H. 1266, drawn by L.S. in his original sketch as a faint elongated group of stars, is omitted by the lithographer. No condensation is shown in any of the seven objects. Fig. 33. - Lithograph agrees pretty well with T.'s drawing, only the objects are not condensed in the middle; besides (1263, 1259 excepted) they are much too bright and sharp. According to present appearance, 1265 should be larger, more condensed at centre and brighter than shown by lithograph; 1258 is now elongated in the direction of the neighbouring star n.; 1259 should be much condensed in the centre; 1260 should be fainter and broader; 1249 should be one minute further north, fainter and also broader.

The lithograph from L.S.'s and T.'s drawings do not agree in some particulars. In L.S.'s drawing the stars are made too large, and several given by T. are not shown by L.S. The most marked difference appears in the patch 1258, which L.S. shows round with a close star n.p. T. shows this patch elongated to a point in a s.f. direction, with the star separated considerably and almost n. ; while B. finds in 1884 it is elongated n. and s., with the star on the n. or pointed end. 1259 and 1265 are bright objects, but the others are extremely faint.

New Nebulae. — Preceding H. 1259 by 79^s.5 and 4′ 30′′ north is a small elongated group of minute stars involved in very thin nebula, and following H. 1265 by 47^s and north 40′′ is a very faint, small, indistinct patch. Neither of these appear to have been hitherto observed.

Nebula 1745 = 3145.

Revised: T. 1876.068; B. 1885.052. The lithograph (M. IV. 34) is from a drawing by T., January 1876.

T., in January 1876, notes as follows:— "Present aspect very unlike H.'s sketch, and so very, very faint that but for this exquisitely clear night I could not have seen it. It is impossible to make out its exact outline, as it appears only as a faint whitishness across the field of view; and in the sketching eye-piece it cannot be seen at all in consequence of the interference of the wires. L.S. searched for it on 27th March 1870, but could not find it, and no wonder, as he remarks that the night was hazy. The slightest particle of haze would prevent this object being seen. As I cannot see it with the sketching eye-piece, the above drawing is rather a random sketch; still it is a fair representation of present aspect. I feel certain that H. could not have seen this object had it been as faint when he observed it as it is at present. Indeed, with regard to a great number of nebulae, the conviction seems forced upon one that they are gradually becoming fainter than formerly."

B. in January 1885, notes:— "Extremely faint, a long streak across the field, straight, very narrow, with a peculiar group of stars in the n.f. quadrant, forming almost a semicircle, of which the north portion of the streak is the diameter. Streak spreads out at its s.p. end, and becomes a large irregular-shaped whitishness, without distinct contour, which the eye cannot see except by moving the telescope up and down, and only when the back ground is perfectly black and free from haze; even then it requires a little time before it can be seen. The present visible portion of this streak, together with this peculiar group of stars, agrees exactly with H.'s drawing and description. The whole object, together with the neighbouring stars, agrees with T. and

with the lithograph. This object has been searched for in vain several times. Position angle of streak measured from diagram 30°. H. gives for this position angle 19°. This discrepancy is unaccountable, since the direction of the streak with regard to the neighbouring stars has not changed. H. calls the length of this 'narrow ray of very feeble light' about 20′ long. I can only see half of this length. It may be that the narrow ray is spreading out continuously into thin whitishness, the whole extent of which cannot be detected by the eye at present. There are two bright stars in the field (11 mag. and 12 mag.). The following is the position of the most southern of the two, which is also the brightest of the group."

The stars are shown in the lithograph too nearly of the same magnitude. The two brightest are the most northerly but one, and the f. one of the three most southerly of the semicircular group.

Nebulæ 2333—36—37—38—40—42= 3324—25—26—27—29—30. (H. IV. 10.)

Revised: T. 1876.380; B 1885.046. The lithograph (M. IV. 35) is from a drawing by T., 19th May 1876.

T., on 19th May 1876 notes as follows:— "H.'s drawing represents this group so fairly that its identification is placed beyond doubt. In his drawing however the cardinal points have all been reversed (very likely an error of the engraver). The two south patches have also been shown too close together, while all the patches are shown too hard and too well defined. This group is situate amid a number of very small stars. Night slightly hazy, but otherwise pretty fine, with good definition." Referring to the lithograph in 1882, T. further remarks:— "It represents very fairly the appearance of the group with the exception of there being no bright streak across the n.p. patch as shown in lithograph." T.'s measures of relative positions are given together with those of B. for comparison.

B., in January 1885, remarks:— "Night very fine, clear, one of the best." 2333. - Narrow, faint streak, much elongated, 90° 80′′ long. 2336. - Extremely faint, cannot see any shape, not elongated, rather large and diffused. 2337. - Very bright, like a segment of a parabola, with a star 12 mag. at the vertex just out of the nebula, condensed, sparkling at the head, diffused, fading away northward. 2338. - Considerably bright, with a star near the centre, soft edged, rather indistinct outline, pretty large, about 70′′ diameter, sparkling, side s. a little better defined than side n. 2340. - Pretty faint, curved, long, touching a star 13 mag., about 2′ in length, diffused, irregular, indistinct, outline, f. side better defined. 2342.- Faint, narrow streak 170°, has a star at its n. end.

The following table contains differential measures, taking the bright star of 10 mag. in the middle of the group as the zero point. T.'s and mine are given together for comparison:—

The above table shows a discrepancy of 7s in R.A. for H. 2342. According to H., his 2342 follows 2338 by 16s.6, which agrees with my observation. It will be seen that all the other measures agree tolerably well together. Reducing the above observations to the centres or most conspicuous parts of the objects, it is found that their present relative positions have not materially changed since H.'s time.

The present appearance of this group agrees with T.'s original drawing and description, except that H.'s 2337 is not so narrow and sharp at the head, but more circular, and the star is not in the nebula, but just touching it; H. 2338, the star involved is not so near the edge n. as shown in his drawing, but much closer to the centre of the object; in H. 2340 there are two stars touching the convex side, one of which is no less than 14 mag. and the other 17; these stars are not shown by T. There are several stars between and near the two central objects of this group which have not been shown by T. The lithograph, when compared with T.'s original drawing, exhibits the following inaccuracies, viz.:— The two central objects, H. 2337 and 2338, should not run into one another, since they are quite detached; and in the s.p. of the two, or H. 2337, the star at the head should be more conspicuous. The n.p. object in the group, viz., H. 2336, is much too bright, and should show no condensation in any part. The n.f. nebula, or H. 2340, is too broad at the end S.; should be more like a crescent.

In the present appearance of the group generally H. 2336, 2337, 2338 and 2340 agree well with H.'s description, although not so well with his drawing; but 2333 and 2342 are very different from both his drawing and description. H. 2333 and 2342 are only two very narrow streaks now and not nearly so broad and oval as H. says. H. 2336 does not show any condensation about the centre at present, and is extremely faint and flat, whereas H. says "suddenly much brighter middle." H. 2337 agrees with his description, but it is now less angular or more approaching a semicircular shape that in H.'s time; also the star which H. says adheres to the nebula is shown in his drawing quite immersed in it, whereas now it only touches it. H. 2338 agrees best of all, only the star which H. places exactly in the centre is now somewhat to the n. of it. Also the North segment is now much fainter than the South, and its edge much less defined than the other. H. does not make this distinction. H. 2340 agrees pretty well with H.'s description and drawing, only the object is not so straight now, but slightly curved like a bow; and there are two stars touching its convex side which are not shown by H."

Eight numbered figures: "1,2, 3, 4, 5, 6, 7, 8"

Note (bottom, left) "Lith^d by E.R. Morris."

Note (bottom, right) "Printed by J Finnie"

[there is no plate 2]

Twelve numbered figures: "20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31"

Note (bottom, left) "Lith^d by E.R. Morris."

Note (bottom, right) "Printed by J Finnie"

Four numbered figures: "32, 33, 34, 35"

Note (bottom, left) "Lith^d by E.R. Morris."

Note (bottom, right) "Printed by J Finnie"