This telescope, the largest and most magnificent that ever was attempted, reflects the greatest honour on the genius, the inventive powers, and the scientific acquirements of its noble contriver, as well as on the elevated station in which he is placed. With rank and fortune, and every circumstance that usually unfit men for scientific pursuit, he has set a bright example to his compeers of the dignity and utility of philosophical studies and investigations, and of the aids they might render to the progress of science, were their wealth and pursuits directed in a proper channel.

Previously to his Lordship’s attempting the construction of his largest—or ‘Monster Telescope,’ he had constructed one with a speculum of 3 feet in diameter, which was considered one of the most accurate and powerful instruments that had ever been made, not excepting even Sir W. Herschel’s forty-feet Reflector. In the account of this telescope, published in the Philosophical Transactions for 1840, his Lordship speaks of the possibility of a speculum of six feet in diameter being cast. At that time, it was considered by some as little short of a chimera to attempt the construction of such a monstrous instrument. But the idea no sooner occurred to this ingenious and persevering nobleman than he determined to put it to the test, and the result has been attended with complete success. The materials of which this speculum is composed are copper and tin, united very nearly in their atomic proportions, namely, copper 126.4 parts, to tin 58.9 parts. This compound has a specific gravity of 8.8, and it is found to preserve its lustre with more splendor, and to be more free from pores than any other. A foundry was constructed expressly for the purpose of casting the speculum. Its chimney built from the ground was 18 feet high, and 16½ square at the base, tapering to four at the top. At each of its sides, communicating with it by flue, was sunk a furnace 8 feet deep, and 5½ square, with a circular opening 4 feet in diameter. About seven feet from the chimney was erected a large crane, with the necessary tackle for elevating and carrying the crucibles from the furnace to the mould, which was placed in a line with the chimney and crane, and had three iron baskets supported on pivots hung round it; and four feet farther on was the annealing oven. The crucibles which contained the metal were each 2 feet in diameter, 2½ deep, and together weighed one ton and a half; they were of cast iron and made to fit the baskets at the side of the mould. These baskets were hung on wooden uprights or pivots, to one of these on each side was attached a lever, by depressing which it might be turned over, and the contents of the crucible poured into the mould. The bottom of the mould was made by binding together tightly layers of hoop-iron, and turning the required shape on them edgewise. This mould conducted the heat away through the bottom, and cooled the metal towards the top in infinitely small layers, while the interstices, though close enough to prevent the metal from escaping, were sufficiently open to allow the air to penetrate. This bottom was six feet in diameter and 5½ inches thick, and was made perfectly horizontal by means of spirit levels, and was surrounded by a wooden frame; a wooden pattern, the exact size of the speculum, being placed on the iron; sand was well packed between it and the frame, and the pattern was removed. Each of the crucibles containing the melted metal was then placed in its basket, and every thing being ready for discharging their contents, they were at the same instant turned over, and the mould being filled, the metal in a short time safely set into the required figure. Whilst it was red hot, and scarcely solid, the frame-work was removed, and an iron ring connected with a bar which passed through the oven, being placed round it, it was drawn in by means of a capstan at the other side, on a railroad, when charcoal being lighted in the oven, and turf fires underneath it, all the openings were built up, and it was left for sixteen weeks to anneal. It was cast on the 13th of April, 1842, at 9 o’clock in the evening. The crucibles were ten hours heating in the furnaces before the metal was introduced, which in about ten hours more was sufficiently fluid to be poured. When the oven was opened the speculum was found as perfect as when it entered it. It was then removed to the grinding machine, where it underwent that process, and afterwards was polished, without any accident having occurred.

This speculum weighed three tons, and lost about one eighth of an inch in grinding. Lord Rosse has since cast another speculum of the same diameter four tons in weight. He can now, with perfect confidence, undertake any casting, so great an improvement has the form of mould which he has invented proved. The speculum was placed on an equilibrium bed, composed of nine pieces resting on points at their centres of gravity; the pieces were lined with pitch and felt, before the speculum was placed on them. The speculum box is also lined with felt and pitched; this prevents any sudden change of temperature affecting the speculum by means of the bad conducting power of the substances employed. A vessel of lime is kept in connection with the speculum-box to absorb the moisture, which otherwise might injure the mirror. The process of grinding was conducted under water, and the moving power employed was a steam-engine of three-horse power. The Polisher is connected with the machinery by means of a large ring of iron, which loosely encircles it; and instead of either the speculum or the polisher being stationary, both move with a regulated speed; the ring of the polisher, and therefore the polisher itself, has a transverse and a longitudinal motion; it makes 80 strokes in the minute, and 24½ strokes backward and forward for every revolution of the mirror, and at the same time 1⁷²/₁₀₀ strokes in the transverse direction. The extent of the latter is ²⁷/₁₀₀ of the diameter of the speculum. The substance made use of to wear down the surface was emery and water, a constant supply of these was kept between the grinder and the speculum. The Grinder is made of cast iron, with grooves cut lengthways, across and circularly on its face. The polisher and speculum have a mutual action upon each other; in a few hours, by the help of the emery and water, they are both ground truly circular, whatever may have been their previous defects. The grinding is continued till the required form of surface is produced; and this is ascertained in the following manner. There is a high tower over the house in which the speculum is ground, on the top of which is fixed a pole, to which is attached the dial of a watch; there are trap doors which open, and by means of a temporary eye-piece, allow the figure of the dial to be seen in the speculum brought to a slight polish. If the dots on the dial are not sufficiently well-defined, the grinding is continued; but if they appear satisfactorily, the polishing is commenced. It required six weeks to grind it to a fair surface. The polisher was cut into grooves, to prevent the abraded matter from accumulating in some places more than in others—a thin layer of pitch was spread over it, it was smeared over with rouge and water, and a supply of it kept up till the machinery brought it to a fine black polish. The length of time employed for polishing the 3 feet speculum was six hours.48

This large telescope is now completed, or nearly so. The tube is 56 feet long, including the speculum box, and is made of deal, one inch thick, hooped with iron. On the inside, at intervals of 8 feet, there are rings of iron 3 inches in depth and 1 inch broad, for the purpose of strengthening the sides. The diameter of the tube is 7 feet. It is fixed to mason-work, in the ground, to a large universal hinge which allows it to turn in all directions. At 12 feet distance, on each side, a wall is built, 72 feet long, 48 high on the outer side, and 56 on the inner—the walls being 24 feet distant from each other, and lying exactly in the meridional line. When directed to the south, the tube may be lowered till it become almost horizontal; but when pointed to the north, it only falls till it is parallel with the earth’s axis, pointing then to the pole of the heavens. Its lateral movements take place only from wall to wall, and this commands a view for half an hour on each side of the meridian—that is, the whole of its motion from east to west is limited to 15 degrees. At present it is fitted up in a temporary way to be used as a Transit instrument; but it is ultimately intended to connect with the tube-end galleries, machinery which shall give an automaton movement, so that the telescope shall be used as an Equatorial Instrument. All the works connected with this instrument are of the strongest and safest kind; all the iron-work was cast in his Lordship’s laboratory by men instructed by himself, and every part of the machinery was made under his own eye, by the artizans in his own neighbourhood, and not a single accident worth mentioning happened during the whole proceeding.

The expence incurred by his Lordship in the erection of this noble instrument was not less than twelve thousand pounds! besides the money expended in the construction of the telescope of three feet diameter. Sufficient time has not yet been afforded for making particular observations with this telescope; but from slight trials which have been made, even under unfavourable circumstances, it promises important results. Its great superiority over every telescope previously constructed consists in the great quantity of light it reflects, and the brilliancy with which it exhibits objects even when high powers are applied. It has a reflecting surface of 4,071 square inches, while that of Herschel’s 40-feet telescope had only 1811 square inches on its polished surface, so that the quantity of light reflected from the speculum is considerably more than double that of Herschel’s largest reflector. This instrument has already exceeded his Lordship’s expectations. Many appearances before invisible in the Moon, have been perceived, and there is every reason to expect that new discoveries will be made by it in the NebulÆ, double and triple stars, and other celestial objects. The following is an extract of a communication from Sir James South, on this subject, addressed to the Editor of the ‘Times.’ ‘The leviathan telescope on which the Earl of Rosse has been toiling upwards of two years, although not absolutely finished, was on Wednesday last directed to the Sidereal Heavens. The letter which I have this morning received from its noble maker, in his usual unassuming stile, merely states, that the metal only just polished, was of a pretty good figure, and that with a power of 500, the nebula known as No. 2., of Messier’s catalogue, was even more magnificent than the nebula, No. 13 of Messier, when seen with his Lordship’s telescope of 3 feet diameter, and 27 feet focus. Cloudy weather prevented him from turning the leviathan on any other nebulous object. Thus, then, we have all danger of the metal breaking before it could be polished, overcome. Little more, however, will be done with it for some time, as the Earl is on the eve of quitting Ireland for England to resign his post at York as President of the British Association. I look forward with intense anxiety to witness its first severe trial, when all its various appointments shall be completed, in the confidence that those who may then be present, will see with it what man has never seen before. The diameter of the large metal is 6-feet, and its focus 54 feet; yet the immense mass is manageable by one man. Compared with it, the working telescopes of Sir William Herschel, which in his hands conferred on astronomy such inestimable service, and on himself astronomical immortality, were but playthings.’

The following is a more recent account of observations made by this telescope, chiefly extracted from Sir James South’s description of this telescope, inserted in the Times of April 16th, 1845, and the ‘Illustrated London News’ of April 19.

‘The night of the 5th of March, 1845, was the finest I ever saw in Ireland. Many nebulÆ were observed by Lord Rosse, Dr. Robinson and myself. Most of them were for the first time since their creation, seen by us as groups or clusters of stars; while some, at least to my eyes, showed no such resolution. Never, however, in my life did I see such glorious sidereal pictures as this instrument afforded us. Most of the nebulÆ we saw I certainly have observed with my own large achromatic; but although that instrument, as far as relates to magnifying power, is probably inferior to no one in existence, yet to compare these nebulÆ, as seen with it and the 6-feet telescope, is like comparing, as seen with the naked eye, the dinginess of the planet Saturn to the brilliancy of Venus. The most popularly-known nebulÆ observed this night were the ring nebulÆ in the Canes Venatici, or the 51st of Messier’s catalogue, which was resolved into stars with a magnifying power of 548, and the 94th of Messier, which is in the same constellation, and which was resolved into a large globular cluster of stars, not much unlike the well-known cluster in Hercules, called also 13th Messier.’ Perfection of figure, however, of a telescope, must be tested, not by nebulÆ, but by its performance on a star of the first magnitude. If it will, under high power, show the star round and free from optical appendages, we may safely take it for granted it will not only show nebulÆ well, but any other celestial object as it ought. To determine this point, the telescope was directed to Regulus, with the entire aperture, and a power of 800, and ‘I saw’ says Sir James, ‘with inexpressible delight, the star free from wings, tails or optical appendages; not indeed like a planetary disk, as in my large achromatic, but as a round image resembling voltaic light between charcoal points; and so little aberration had this brilliant image, that I could have measured its distance from, and position with any of the stars in the field with a spider’s line micrometer, and a power of 1,000, without the slightest difficulty; for, not only was the large star round, but the telescope, although in the open air, and the wind blowing rather fresh, was as steady as a rock.’

‘On subsequent nights, observations of other nebulÆ, amounting to some 30 or more, removed most of them from the list of nebulÆ, where they had long figured, to that of clusters; while some of these latter, more especially 5 Messier, exhibited a sidereal picture in the telescope such as man before had never seen, and which for its magnificence baffles all description. Several double stars were seen with various apertures of the telescope, and with powers between 360 and 800; and as the Earl had told us before we should,—before the speculum was inserted in the tube, in consequence of his having been obliged to quit the superintendence of the polishing at the most critical part of the process,—we found that a ring of about 6 inches broad, reckoning from the circumference of the speculum, was not perfectly polished, and to that the little irradiation seen about Regulus was unquestionably referable. The only double stars of the 1st class which the weather permitted us to examine with it were Xi UrsÆ Majoris, and Gamma Virginis, which I could have measured with the greatest confidence. D’Arrest’s comet we observed on the 12th of March, with a power of 400, but nothing worthy of notice was detected. Of the Moon, a few words must suffice. Its appearance in my large achromatic of 12 inches aperture is known to hundreds of readers; let them then imagine that with it they look at the moon, whilst with Lord Rosse’s 6 feet they look into it, and they will not form a very erroneous opinion of the performance of the Leviathan. On the 15th of March, when the moon was 7 days old, I never saw her unilluminated disk so beautifully, nor her mountains so temptingly measurable. On my first looking into the telescope, a star of about the 7th magnitude was some minutes of a degree from the moon’s dark limb, and its occultation by the moon appeared inevitable. The star, however, instead of disappearing the moment the moon’s edge came in contact with it, apparently glided on the moon’s dark face, as if it had been seen through a transparent moon, or as if the star were between me and the moon. It remained on the moon’s disk nearly two seconds of time, and then disappeared. I have seen this apparent projection of a star on the moon’s face several times, but from the great brilliancy of the star, this was the most beautiful I ever saw. The cause of this phenomenon is involved in impenetrable mystery.’

The following is a representation of the Great Rosse Telescope, along with part of the buildings with which it is connected. In the interior face of the eastern wall a very strong iron arc of about 43 feet radius is firmly fixed, provided with adjustments, whereby its surface facing the telescope may be set very accurately in the plane of the meridian. On this bar, lines are drawn, the interval between any adjoining two of which, corresponds to one minute of time on the Equator. The tube and speculum, including the bed on which the speculum rests, weigh about 15 tons. The telescope rests on an universal joint placed on masonry about 6 feet below the ground, and is elevated or depressed by a chain and windlass; and although it weighs about 15 tons, the instrument is raised by two men with great facility. Of course, it is counterpoised in every direction. The observer when at work, stands in one of four galleries, the three highest of which are drawn out from the western wall, while the fourth or lowest has for its base an elevating platform, along the horizontal surface of which a gallery slides from wall to wall by a machinery within the observer’s reach, but which a child may work. When the telescope is about half an hour east of the meridian, the galleries, hanging over the gap between the walls, present to a spectator below an appearance somewhat dangerous; yet the observer, with common prudence, is as safe as on the ground, and each of the galleries can be drawn from the wall to the telescope’s side so readily, that the observer needs no one else to move it for him.

figure 98.