Dedicated to the memory of Peter Grego (1966-2016).
The picturesque, rural town of Birr in the County of Offaly, lies at the geographic centre of the Irish Republic. Inhabited in some capacity since the Bronze Age, a monastic settlement was established there by St. Brendan the Elder, which probably dates to the 7th century AD, and in the centuries that followed, Birr became the ancestral home of the O’ Carroll clan, the ruling Gaelic family of the northern territory of the ancient kingdom of Éile. In the aftermath of the Norman invasion of the 12th century, a castle was built there and continued to be administered by the O’Carroll’s, who were required to pay tribute to the Butlers of Ormonde, overlords of the district, whose capital was established in the neighbouring county of Kilkenny. In the aftermath of the English Plantation of Ireland in the 17th century, Birr Castle became the seat of the Parsons dynasty, the Earls of Rosse, beginning in 1620, when the civic areas were annexed to it, subsequently becoming known as Parsonstown.
From the 17th century onwards the Gaelic Irish were reduced to the status of tenants and landless peasants on their ancestral lands. Members of the O’Carroll clan were however, granted new lands in the colonies of Maryland and one family descendant, James Carroll of Carrolltown, went on to become the sole Catholic signatory of the American Declaration of Independence.
Evidence of British colonial rule can still to be seen in the elegant Georgian architecture of the modern town, with its tree-lined malls, and well-planned avenues, which still have the power to delight the eye. A railway, printing works and distillery provided employment to local families and a workhouse offered some relief to the starving peasants, a million of whom lost their lives during the famine years. A garrison of English soldiers was also established in the town. But like all Irish municipalities once administered by the iron fist of British Imperialism, the political winds of change swept rapidly through the region, as agrarian agitation by the Fenians, Land League and the Irish Parliamentary Party led to the dissolution of the landlord system, which also included the estate of the Earls of Rosse. As a symbolic act of the new order, the Gaelic Athletic Association also held the first All-Ireland Hurling Final at Birr in 1888. Remarkably, though its population was decimated in the mid-19th century owing to the ravages of the Irish potato famine (1845-52), the modern town of Birr, the inhabitants of which number about 6,000, has scarcely grown in size from its pre-famine population, making it one of the most pristine Irish heritage towns in existence.
After Birr Castle became Crown property in 1620, the Parsons family held several key offices in the administration of Ireland. William Parsons became Commissioner of Plantations and Surveyor-General of Ireland. His brother, Sir Laurence Parsons, became Attorney-General for the province of Munster and in the years that followed, the Castle was considerably enlarged and a successful glass works established which further aided the local community with employment opportunities. In the aftermath of William Parsons’ death in 1628, Birr became the epicentre of conflict between Catholics and Protestants. In 1641, a rebellion by Irish Catholics broke out. In January 1642, the castle itself was besieged by the Molloys, Coghlands and Ormonders , the factions engaging in brutal combat for five days. In some desperation, the noble incumbent, William Parsons, son of Sir Laurence, fled to the English army stationed at Dublin, and never returned. He died in 1653.
The troubles escalated during the time William’s son, Laurence, took up residence at Birr Castle after he father’s passing. This time, England was faced with the prospect of crowning a Catholic King, the Duke of York, who became James II in 1685. Laurence Parsons and his family departed for London leaving an unscrupulous heathen in charge of running the family estate at Birr, a one Colonel Heward Oxburgh, who, in 1689, seized complete control of the castle and its garrison, using it as a base for the forces loyal to William of Orange. Sir Laurence together with two of his confidants, were placed on trial by Oxburgh, accused of being traitors to King James II, the last Catholic King to rule the British Isles, but were later granted a reprieve and rescued by William’s men.
More turmoil followed, when in 1690, the Castle was once again besieged by an army led by the Duke of Berwick, an illegitimate son of James II, who himself was not long deposed in the Glorious Revolution of 1688. During the exchange of fire, cannon balls flew through the parlour window, leaving marks in the walls of the north flanker which can still be seen to this day. Lady Parsons was even forced to relinquish the lead cistern she used for salting beef so that it could be melted down for bullets. Eventually though, the besieging army was finally repulsed, and the Parsons family returned to relative peace thereafter. The bloody events of the 17th century marked a watershed in the history of the castle, as well as the family who made it their home. A new dynasty of Parsons were to emerge from the ashes.
Throughout the 18th century, Birr castle became a popular haunt for some of the must cultivated individuals in Europe. Sir William Parsons, the 2nd baronet(in the new regime), was a close friend of the gifted composer, Georg Frideric Handel, who gave him an engraved walking stick in appreciation of the patronage which led to his magnum opus – Messiah – being first performed in Dublin. His grandson, another Sir William, the 4th baronet, began an ambitious project of landscaping the grounds of Birr Castle. Transforming bog land into an ornate lake, he planted beech trees and demolished the last of the ancient towers of the original fortress so as to complete the sweeping view of the demesne.
Sir William also devoted much of his time to the Volunteer movement, which sprang up towards the end of the eighteenth century, ostensibly to defend Ireland from the threat of French invasion, but effectively to force the English government to give concessions to the Irish Parliament. His son, Sir Lawrence, 5th baronet, became well-known as a patriot statesman, whose friend and colleague, the Irish revolutionary, Theobald Wolfe Tone(1763-98), referred to him as ‘one of the very very few honest men in the Irish House of Commons’. This personal integrity led him not only to oppose the Union with all his strength, but also to expose the bribery the British used to push it through. Evidently disgusted with the passing of the Act of Union in 1800, Sir Laurence retired from politics at the beginning of the 19th century, though he later accepted the post of Joint Postmaster General and attended the laying of the foundation stones of Dublin’s magnificent General Post Office build during his term of office. He devoted the autumn years of his life to literature.
Sir Laurence, the second Earl of Rosse, had three sons, the eldest of whom, William (also known as Lord Oxmantown), succeeded his father as third baronet upon his death in 1841. Unlike his father before him, the third Earl had a penchant for all things scientific, especially astronomy, and we learn of his first forays in the art of telescope making as early as 1827. The illustrious career of Sir William Herschel (1738-1822) proved to be a huge influence on the young William Parsons (1800-67), inspiring him to read mathematics at Trinity College, Dublin, where he graduated with a first class honours degree in 1822. And although he resolved to embark on a scientific career, his baronial status required that he take part in public life. To that end, he entered Parliament for King’s County (later renamed Offaly) in 1823, where he enjoyed a reasonably successful career, which he brought to an end in 1834. Two years later he married Mary Wilmer-Field, who hailed from Heaton, Yorkshire. The marriage was a long and happy one, and together they had four sons, all of whom displayed considerable intellect in adult life. Lady Mary was also a gracious host for all the scientists who were to work at Birr, and took an active interest in the work of her husband. The couple took up residence at Birr castle after William’s parents retired to Brighton, England, in search of milder climes. As master of his own baronial home, William was free to pursue his scientific career.
William Parsons lived in a singularly interesting time for telescopic astronomy. Refracting telescopes were justifiably popular, especially after the innovations heralded by the genius of Joseph von Fraunhofer(1787-1826) in Germany, who had brought high quality achromatic refractors to market astride state-of-the-art clock-driven mounts that gracefully tracked celestial objects as they moved across the sky. But Parsons was a scientist, and he was compelled to pursue reflectors rather than refractors owing to the very limited aperture of the latter. He wanted to see the nebulae of Messier and Herschel better than anyone before him. Perhaps he had seen too many of his astronomical acquaintances follow the fashions of the time; which almost invariably involved double star mensuration with small aperture refractors. Indeed, according to the late Sir Patrick Moore, he completely abandoned the refractor early in his astronomical career. Parsons had clearly decided to go after bigger fish, and was convinced that mirrors were the way to go. And to that end, he set about grinding his own.
Like many astronomers of his day, Lord Oxmantown had to learn the noble art of casting and grinding mirrors to the required geometrical shape from scratch. He was vociferous about making the details of the construction of fine optical wares public knowledge, condemning the often secretive culture of telescope makers who came before him. As was the custom in those days before silver-on-glass reflectors, he had to use speculum metal mirrors consisting of an alloy of copper and tin as the reflective surface (discussed in much greater detail in this author’s up-and-coming book). To this end, he employed his considerable inventiveness to construct a steam-powered grinding machine with a power output of 2 horse power (~1.5KW). The mirror blank, placed in a vat of water to prevent its over-heating and expansion, was rotated slowly by the contrivance whilst the polishing ‘tool’ was made to move to and fro across the metal surface by a couple of cranks placed at right angles to each other. By considerable trial and error, Oxmantown was able to construct a series of increasingly large specula, first a 15-inch and then a larger 24-inch, both of which proved to be of very high quality.
Unlike Herschel before him, who had dispensed with the use of a secondary flat mirror in order to conserve the amount of light reaching his eye, and which gave rise to the tilted mirror of the Herschelian design, Lord Oxmantown returned to the closed-tube Newtonian configuration, finding out by experiment, that it reduced turbulence on account of the observer being located at a large enough distance from the mouth of the open tube. He also showed that tilting the mirror in the Herschelian fashion introduced unwanted aberrations to the images that were much less manifest in the Newtonian design. His mounting strategy, however, was quintessentially Herschelian in form, with all its attendant weaknesses.
After many false starts and setbacks, he managed to cast and figure a fine 36-inch speculum with a focal length of 27 feet (f/9 relative aperture) in 1839. The mirror was an alloy of 126.4 parts copper with 58.9 parts tin which produced a fine, white metal. The optical flat mirror was tested by comparing a distant object in daylight, first with a fine achromatic telescope and then using the same telescope that had formed an image after its reflection in the mirror. Any distortions would have been readily seen and adjustments accordingly made. After mounting the optics, Oxmantown’s friend, the distinguished mathematician (a pioneer in vector algebra), William Rowan Hamilton(1805-1865), whom he became acquainted with during his time at Trinity College, was the first to turn it on celestial targets, and later pronounced it as excellent. Lord Oxmantown also invited the distinguished astronomers, Sir James South (of double star fame) and Thomas Romney Robinson, to his estate at Birr Castle in order that they might test the telescope and pronounce assessments of its quality. Having just spent a considerable amount of time performing similar tests on the 13.3-inch (with an objective by Cauchoix) refractor at Markree Castle, Co. Sligo, first dedicated in 1834, the gentlemen astronomers stayed at Birr between October 29 and November 8 1840. The guest astronomers were duly impressed with Lord Oxmantown’s newly erected 36-inch, pronouncing it “the most powerful telescope that has ever been constructed,” and declaring it superior even to the late Sir William Herschel’s 48-inch behemoth. On all objects studies, which included, the Moon, double stars, open stellar clusters and nebulae, the 36-inch showed its optical excellence. Indeed, according to Robinson (who became the first Director of Armagh Observatory in 1823):
“It [was] scarcely possible to preserve the necessary sobriety of language, of speaking of the Moon’s appearance with this instrument, which discovers a multitude of new objects at every point of its surface.”
Robinson observed lunar features at a power of 900 diameters with the 36-inch reflector that were scarcely seen again for another 60 years, including the appearance of “two black parallel stripes in the bottom of Aristarchus,” which are now known to be depressions, and a series of “extremely minute craters” on the ridges of the crater Ptolemaeus.
Robinson also observed M31 in Andromeda and the Great Nebula in Orion (M42) in the hope that the great telescope at Birr might resolve them into stars. Examination of the Dumbbell Nebula (M 27) in Vulpecula and the Ring Nebula (M57) in Lyra showed that they remained wholly nebulous in the 36-inch. Alas, while he detected the tell-tale signs of individual stars on the edges of M31, the results were at best ambiguous and only served to strengthen his conviction that these objects were fundamentally non-stellar in origin. Star clusters such as M13 and M92 in Hercules were reportedly breathtaking at high powers though the same instrument.
Lord Oxmantown was satisfied that he had indeed created a first-rate telescope that would contribute to scientific knowledge, and in the spirit of the age, warmly welcomed the finest observers across Europe to use the telescope for their researches:
“Although the instrument and the laboratory where it was constructed are in the centre of Ireland,” he wrote, “the facilities of communication are such that those who desire further information can easily obtain it on the spot, and from their own estimate of the performance of the instrument”.
His invitation was enthusiastically accepted, and in due course, distinguished scientists and observers of the ilk of Sir John Herschel, George Johnstone Stoney, William Lassell, Otto Struve, George Bidell Airy, Franz Friedrich Brünnow and George Gabriel Stokes, all enjoyed time at the great telescopes designed by Lord Rosse.
Yet, as soon as the 36-inch was completed, Oxmantown had made plans for an even greater instrument that would remove the still pervasive ambiguity concerning the nature of the celestial nebulae:
“I think that a speculum of 6 feet aperture could be made to bear a magnifying power more than sufficient to render the whole pencil of light, and that in favourable states of the atmosphere it would act efficiently, without having recourse to the expedient, which Newton pointed out at the last resort, that of observing from the vantage of a high mountain…… an instrument even of the gigantic dimensions I have proposed might, I think, be commenced and completed within one year.”
In making the 72-inch reflector a reality, Oxmantown was faced with a daunting task. A mirror twice as large would have four times the area of the smaller 36-inch and would be much more difficult to successfully cast, grind and polish. Its much greater weight would make it considerably more challenging to mount stably as well. As Robinson later pointed out in a paper presented in 1845; it was not possible to melt down the appropriate quantities of copper and tin in the crucible used to create the 36-inch speculum. Indeed, three such crucibles would be called for, each 24 feet in diameter and weighing half a ton apiece. Oxmantown had to construct a giant chimney-shaped furnace to accommodate the three crucibles. To achieve the necessary temperatures to create the liquid alloy, 2000 cubic feet of turf cut from a local peat bog had to be combusted for ten hours before the melt was ready. It must have been quite an apparition to catch sight of the thick yellow smoke billowing upwards from the giant furnace, its eerie yellow and orange glow being clearly visible for miles around. The cylindrical metal blank, weighing in at a whopping 4 tons, was successfully cast, but an accident of some unknown nature occurred one month into figuring the giant metal slab with the result that a large crack rendered it useless. Undeterred, a plan was made to recast the same metal, and this time it was accomplished, though it was slightly thinner than the original, weighing a half ton less. The subsequent grinding and polishing phases also went well, and by April 13 1842, the mirror was completed.
Lord Rosse had to tread very carefully in considering the mounting for this giant telescope. The tube would be 58 feet long and as a result, it would not be possible to mount it in the way the 36-inch telescope was. If a Herschelian type mount were to be employed, the slightest breeze would set the giant telescope- which would weigh over 150 tons when completed – swinging wildly from side to side, not only making observations impossible, but putting the lives of the observers and workmen operating the instrument in jeopardy. After much deliberation and consultation, Oxmantown settled on a mounting system set between two massive walls. These would be 70 feet long and 50 feet high, running parallel with the north-south line, so that celestial objects could only be examined as they crossed the local meridian. Indeed, for an object located on the celestial equator, the total viewing time would be restricted to an hour at most. But at least the great telescope would be able to view its target when it was highest in the sky and so less affected by atmospheric turbulence.
Construction started on the Parsons demesne at the end of 1842 and continued right the way through 1843 and 1844. A cast iron joint – similar to a modern universal joint – occupied the base of the mount, and upon it was bolted an 8 foot wooden box that would carry the giant mirror. Around this was placed the telescope tubing, fashioned from inch-thick staves, and held in position by a series of iron clamp rings. The tube tapered down to 7 feet at its extremities, making it a rather odd, cigar shape. Movement in declination was undertaken via a series of thick metal cables fastened to the top of the telescope, and maneuvered by a system of elaborate pulleys. Right ascension (to and fro) motion was accomplished with a manually-operated steering wheel. In addition to these course movements in both right ascension and declination, provision was made to allow fine adjustments in both axes to centre the object under study. Oxmantown also had the presence of mind to install finely meshed screens under the telescope, so as to protect workers from the accidental fall of eyepieces and other items of equipment. The financial outlay of the Leviathan was very considerable: £12,000 in the currency of the day!
Observing with the great telescope was never a solitary affair. Indeed, its operation always required a well-trained team of operators, who had to follow verbal instructions from the astronomer assigned to it on any night. Nor was the telescope ever fitted with a finder telescope! Instead, Oxmantown employed a low power, wide field ocular of his own design, with a magnification of 216 and possessing a generous true field of 31 arc minutes (so just large enough to show the full Moon) to centre objects to be studied. And while he had intended to install a clock drive to move the instrument in right ascension, in the end, this never came to fruition, neither under the Third Earl’s watch or that of his son, the Fourth Earl. After undertaking a series of mechanical trials over the winter of 1844, the instrument was deemed ready for operation in February 1845, when both Robinson and South were once again invited to Birr Castle to provide an assessment of its efficacy.
Alas, the weather didn’t cooperate and opportunities to test the Leviathan were few and far between. First light came for an hour or so on the evening of February 15, when the telescope was turned on Castor, a famous double star in the constellation of Gemini. To the delight of all in attendance, the system was easily and cleanly split, the components appearing more brilliant than any other telescope in existence. Next, the great light bucket was directed at M67, a small open cluster situated across the border into Cancer. Robinson and South reported that the faint stars in the cluster were magnificently rendered. Then the clouds rolled in again. And with further inclemencies in the weather occurring over the next couple of weeks, it was decided to remove the primary mirror for further polishing – no mean task in itself as it required the combined effort of 25 or 30 workmen!
While it is unquestionably the case that the 72 inch Leviathan of Parsonstown was very unwieldy by modern standards, Sir James South reported that he could uncap the telescope, have its position adjusted by the assistants on both axes and have a star centred for observing in about eight minutes! Second light occurred on March 4, where a spell of settled weather made observations possible up until March 13. No opportunities were missed to turn the great telescope on a suite of double stars, open clusters and nebulae that hugged the meridian at that time. It was over this period that Robinson and South declared the instrument optically excellent and capable of doing first class astronomical research. Shortly thereafter, the telescope was officially inaugurated by Dean Peacock, head of the (Protestant) Church of Ireland, who is said to have walked through the giant tube, inspecting it from one end to the other whilst donning a top hat with a raised umbrella above his head. In the milder months that followed, the Leviathan was turned on the nebula listed as number 51 in Messier’s famous catalogue (see the author’s previous chapter on Charles Messier), located in the Canes Venatici, was examined and its spiral structure clearly seen; a momentous discovery for sure, but one that was overshadowed by more terrible events.
The summer of 1845 marked an atrocious turning point in the history of this small nation. By now, the potato famine was palpably showing its devastating effects (with 50 per cent of the crop having being infected with blight), and the peasants who worked the land throughout the county were beginning to starve. Lord Rosse was by now a peer in the British House of Lords, and still served as Lord Lieutenant and Colonel of Militia of Kings County. Admirably though, he put the needs of his countrymen first and after consulting with the British Prime Minister, Sir Robert Peel, and his panel of appointed scientific experts, provisions were made to import cheaply purchased maize and cornmeal from the New World, which helped somewhat but could not fully ameliorate the human disaster.
It was not until January of 1848 that Lord Rosse would resume active research with the great telescope. But when it was uncapped after a three year hiatus, the mirrors were found to have tarnished owing to the excessively damp weather that characterised the worst of the famine years. And though a second mirror had by then been successfully cast, it had not been polished to the required degree. But by February 16 both specula were ready for action and by month’s end, astronomical observations were in full swing once again. Indeed the great telescope remained in active service for many years thereafter. The magnificent instrument became the centrepiece of international attention, and tourists flocked to see it from all around the world. And it was all the more remarkable that its creator did it all off his own back, with no financial assistance from governments or monarchs, quite unlike the situation with Sir William Herschel (discussed in another chapter of the book).
According to research conducted by the late Sir Patrick Moore, the defining power of the Leviathan was called into question by a number of individuals, mostly casual observers, but affirmed by those who had been given the opportunity to observe with it on a regular basis. One such tyro is reported to have remarked:
“They showed me something which they said was Saturn, and I believed them….“
But the reader should note that such a monstrous telescope, with such a large aperture as it possessed, was much more sensitive to atmospheric turbulence than instruments of much smaller aperture, particularly the equatorially mounted classical refractors, which by now were adorning the observatories across Europe and North America.
Consider, if you will, the remarks of the distinguised Irish physicist and astronomer, George Johnstone Stoney (1826–1911), himself a native of the town of Birr, whose reputation as an observer was unquestioned and who carried out careful tests on the 72 inch instrument over an extended period of time (four years to be precise, over the period 1848-52):
The test usually applied was the performance of the mirror on the star of the 8th or 9th magnitude, magnification 750. Such stars are bright in the great telescope. They are usually seen as balls of light, like small peas, violently boiling in consequence of the atmospheric disturbance. If the night is good there will be moments now and then when the atmospheric disturbance will abruptly seem to cease for a fraction of a second, and the star is seen for an instance as the telescope really presents it. It is by the opportunities of such moments that the performance of the telescope must be judged. With the best of your father’s* mirrors that I saw, the appearance at such opportunities was that of the light shining through a minute needle hole in a card placed in front of a flame. I think any practical astronomer will agree with me in the opinion that mirrors of 6 feet in diameter that bore the test bordered very closely indeed on theoretical perfection.
* Stoney is referring here to the third Earl of Rosse, but the communication was to his son, who succeeded to the title of fourth Earl by the time the scientific correspondence was published on April 2 1878.
As King Solomon of old knew, there is really nothing new under the Sun. Then, as now, casual observations are not likely to reveal any great truth but rather have the greater potential to disseminate untruth.
Indeed Moore, in his book, The Astronomy of Birr Castle, provides still more evidence that the mirrors made by the third Earl of Rosse were of high quality. In February of 1848, shortly after the Leviathan was dedicated, Romney Robinson described a fine night in which Jupiter presented with a ” remarkable appearance… full of faint striae running nearly parallel to them, and seemingly belonging to the brighter zones on each side.” And in 1889, a series of published drawings of Jupiter made by a later assistant of Lord Rosse, Dr. Otto Boeddicker between 1881 and 1886, show that they compared well with modern instruments of the same size, according to the noted planetary observer, Stanley Williams, who conducted such a study in 1935.
Still more evidence of its optical quality can be gleaned from a discussion of the telescope in Henry C. King’s classic tome, The History of the Telescope, where he notes that the Leviathan was capable of resolving very tight double stars. On one occasion, Robinson, South and Lord Oxmantown managed a clean split of gamma 2 Andromedae with a power of 828 diameters and a then separation of 0.5″.
Such testimonies show that while the telescopes of Lord Rosse were not ‘planetary’ instruments in the traditional sense (for they were seldom employed in this arena), they were more than capable of doing first rate science.
The enormous light gathering power of the Leviathan added to the tally of spiral nebulae. Indeed, by the end of 1850, a total of 14 such structures were positively identified by Lord Rosse and his astronomical assistants. These included M33, M31, M77, M95 and M99. It was even possible for Lord Rosse to begin to subclassify these spiral nebulae into a variety of classes, including barred, diffuse and irregulars. He also suspected that many of the elliptical and lenticular nebulae the surveys showed up must be spiral also but that they were seen ‘edge on’ rather than ‘face on’. The spiral nature also strongly suggested to him that their complex shapes could only be maintained by motion, although he recognised that making any such measurements was hopelessly beyond his means, as they were so far away.
One enduring mystery concerning the discovery of the spiral nebulae pertains to why the keen eye of Sir William Herschel was unable to detect them as such. It is most certainly true that the brighter spiral nebulae should have been visible in his largest telescope; the celebrated 40 foot reflector outfitted with a 49.5 inch primary speculum. One explanation, advanced by this author, may lie in Hercshel’s decision to adopt his off axis (Herschelian) design, which, as we have learned, introduced some aberrations to the images which reduced the instrument’s defining power enough to render the faint and delicate spiral arms all but invisible. Evidence in support of this comes from Herschel’s failure to detect the E and F stars of the theta Orionis complex, as well as the fact that he almost invariably employed low powers with this instrument (much of his fine planetary work was conducted with a much smaller instrument; a conventional long focus Newtonian of 6.3 inch aperture) Yet another possibility is that Herschel may have observed such objects when his mirrors were in a more advanced state of tarnishing. In a work published by William F. Denning, we are made aware that slight tarnishing (of a silver substrate) could often be useful in improving planetary images, acting in much the same way as a modern neutral density filter, which can reduce glare and improve contrast. But this would not be the case with deep sky objects, where even slight tarnishing will apprecibaly reduce the so called “space penetrating power,” as Herschel referred to it, helping to explain why he did not see the spiral structures which were so obvious to Lord Rosse and his assistants. That said, without some form of reconstructive experimentation, we shall probably never know the precise reasons for this anomaly.
One of the most important questions still to be resolved(excuse the pun) was the nature of nebulae in general. Sir John Herschel (discussed at length in another chapter) had formed the opinion that all nebulae would eventually be resolved into stars, but Lord Rosse was more open minded about this. Telescopic scrutiny of many objects with the Leviathan, including M1 (the Crab Nebula, as coined by Lord Rosse himself), M27, M56 and M97 did not show stellar constituents, so the jury was still out concerning this question. But there was always nagging doubts that the mirror might not have been gathering the amount of light it was capable of due to rapid tarnishing in the humid, southern Irish climate. Concerning this possibility, Lord Rosse wrote:
We have had perhaps two or three specula as perfect as the first one; but the mass of observations has been made with specula considerably inferior to it, and, I am sorry to say, very often not as bright as they should have been…..While the telescope was in constant use in all weathers, it would have been a hopeless task to attempt to keep in a state fit for the resolution of nebulae, and the attempt was not made. I may, perhaps, mention that with the 3 feet speculum in fine order I have often detected resolvability when there was no trace of it with the 6 feet speculum in its ordinary working state.
That said, Lord Rosse’s caution concerning the universality of stellar nebulae was vindicated just over two decades later, when in 1864 William Huggins employed spectroscopy to show that some nebulae were distinctly different from those of stars.
As discussed previously, Lord Rosse did not employ a finder with the telescope, relying instead on the 31 arc minute field in the ‘low power’ setting. Oculars of various focal length were placed on an elegant sliding mechanism so that the observer could move from low to high power with little or no delay. The Leviathan was also fitted with a micrometer, the proper operation of which was a necessity for making the elaborate drawings of deep sky objects with their correct scale.
Records show that the instrument could be used about 60 nights per year, but in retrospect, it seems rather odd that Lord Rosse would choose to erect the great telescope so close to the Bog of Allen (from which the turf was derived to power the furnaces for the molten optical metal), which encouraged fog banks to form on still evenings, further reducing its utility. But at least it served to warn later generations of giant telescope makers to pay closer attention to the observing site before committing to some ambitious project. Indeed, nearly all later telescopes of grand esate were erected upon sites that were carefully field tested prior to the commencement of any building.
The great telescope and the opulent milieu in which it was erected became a Jerusalem of learning for two generations of astronomers, many of whom made their astronomical debuts observing with the great telescope. In 1852, Oxmantown hosted a meeting of the British Lunar Committee in the grounds of Birr Castle. As a general rule, Lord Rosse employed many young observers (no doubt owing to their enthusiasm for astronomical work and keen vision), who served at the telescope for a number of years before moving on to other observatories in order to further their careers. For example, Robinson served as the first Director of Armagh Observatory (a post he held until he was 90!), and a young Sir Robert Stawell Ball, who served as an astronomical assistant at Parsonstown between 1865 and 1867, as well as an academic tutor to Lord Rosse’s children, would be a future Astronomer Royal for Ireland (based at Dunsink Observatory, Dublin, between 1874 and 1892), before being appointed to the prestigious position of Lowdean Professor of Astronomy at Cambridge University in 1893. Of Lord Rosse, Sir Robert graciously observed, “personally and socially, [he] endeared himself to all with whom he came in contact.”
Lord Oxmantown, the third Earl, maintained an active role as an observer until failing health in the early 1860’s forced him to give up routine astronomical work, entrusting all research to the assistants whom he assiduously trained. In the summer of 1867, on the advice of his physicians, the ageing peer retired to the seaside residence of Monkstown, overlooking Dublin Bay, in the hope that the fresh, maritime air would improve his condition. But it was to no avail. He passed away peacefully on October 31 of the same year.
It was at about the same time that Lord Rosse’s eldest son (1840–1908), the fourth Earl, began to take on more of an active role in his father’s work. Born and raised in Birr, he was educated at Trinity College, Dublin, and Oxford University, before returning to Ireland to serve in various high profile roles in the administration of Ireland. Though largely considered to be overshadowed by the achievements of his father, Lawrence Parsons embraced the new technologies that were coming to the fore, having first experimented with a newly erected 18 inch reflector of ten feet focus, which was ingeniously powered by a water wheel in 1866. In the years that followed, the fourth Earl managed to construct partially successful clock drives for both the 36 inch and 72 inch telescopes.
The provision of crude clock drives on the two great telescopes enabled more sophisticated science to be performed and, in this capacity, crude spectroscopic analyses of a variety of deep sky objects was carried out. Much of this important work was carried out by a young Dane, John Louis Emil Dreyer (1852–1926), who had put down roots by marrying a lassie from County Limerick, serving as assistant astronomer at Birr between 1874 and 1878. All the spectra obtained on the spiral nebulae were shown to be stellar in character, while all those obtained from the planetary nebulae showed quite distinctive line spectra, further advancing the notion that there were fundamental differences in the nature of nebulae.
Dreyer used the Leviathan to add a considerable number of newly discovered nebulae to the tally already discovered by his illustrious predecessors (particularly Messier and the Herschels). Many of these new objects were recorded in a catalogue compiled by the fourth Earl covering the three decades between 1848 and 1878. Another notable discovery was made by the English astronomer, Ralph Copeland (1837–1905), who served as assistant astronomer at Birr between 1871 and 1876, used the enormous light gathering power of the Leviathan to discover 35 new NGC objects, most famous of which is a grouping of seven large galaxies in Leo – Copeland’s Septet as it is known today, that include NGC 3745, 3746, 3748, 3750, 3751, 3753, and 3754.
The fourth Earl of Rosse is perhaps best known for his work in determining the surface temperature of the sunlit face of the Moon. For decades, astronomers such as Piazzi Smyth and Macedonio Melloni ( inventor of the first infrared thermopile in 1831, which transduced thermal energy into electrical energy) had wondered whether the Moon would have an equable temperature like the Earth, and to this end had carried out the first crude experiments in its determination with results which turned out to be mostly inconclusive.
Determining the temperature of the Moon is far from trivial however, as a moment’s reflection (excuse the pun once again) will reveal. Lord Rosse correctly concluded that the contribution of thermal energy from lunar vulcanism was negligible. That leaves two principal sources of heat. First, there will be that which is reflected. This will be largely independent of the temperature of the moon’s surface, but rather will depend only upon its power of reflection (its albedo). The second contributor to lunar heat is that which she emits as a consequence of her natural heat which is mainly, but not entirely, due to solar irradiance. The amount of this heat will depend upon the temperature of the Moon’s surface and its radiating power. Though the thermopile could not readily distinguish between these two sources of heat, Lord Rosse realised that they would vary differently in accordance with the development of the lunar phase, with the former increasing steadily from thin crescent and reaching a maximum at full Moon, whilst the latter ought to lag behind the former, as a consequence of the time it takes for the surface to heat up (in much the same way as daytime summer temperatures reach their maximum several hours after noon). Thus, this ‘dark’ (infrared) heat ought to be at its maximum after full Moon.
Lord Rosse begun such measurements using the 36 inch reflector in 1868 and the careful work continued for several years. His first estimates showed that the lunar surface temperature near the equator could reach 500 degrees Fahrenheit (260C), but with subsequent refinements made by his fellow physicists, he later revised this down to just over 200 degrees Fahrenheit (or about the boiling point of water at sea level). The latter measure agrees well with the modern accepted maximum value of 253 Fahrenheit.
Of course, the temperatures arrived at by Lord Rosse referred to the equator, in the middle of a long lunar day. Naturally, the further away from the equator one moves, the cooler the surface becomes. He peformed similar experiments during a lunar eclipse, when its surface is cut off from all direct sunlight. Indeed, he was able to monitor a rapid drop in lunar surface temperature as a ‘wave of cold’ moved across its surface. Indeed, he was able to record enormous temperature swings in the course of an hour. This provided further proof that the Moon is an airless world, incapable of holding onto heat as it moves from direct sunlight into darkness.
By the 1880s, the Leviathan was most definitely showing its age and many astronomers felt that its best days were well behind it. Indeed, from the late 19th century onwards the 72 inch was mostly used in sporadic observations of interesting objects. For example, on the night of September 17 1877, Lord Rosse was able to confirm the existence of the tiny Martian satellites, Deimos and Phobos, discovered by Professor Asaph Hall, just a few short months before using the great Washington refractor. The last and longest serving assistant assigned to the Leviathan was the aforementioned Dr. Boeddicker, who concerned himself with detailed visual observations of the northernly Milky Way, which culminated with an extraordinarily detailed drawing of the vast stellar archipleagos within its confines, taking him no less than five years to complete, beginning in 1885 and coming to an end in 1890. Doubtless, it was a work of outstanding artistic beauty but alas, photography was now all the rage, and as a consequence, its significance was of questionable scientific value. And while the venerable 36 inch was now equatorially mounted with a smootly operating clock drive, and even in the hope that it might be used as an astrograph, the declining relevance of the antiquated Leviathan weighed heavy on the fourth Earl’s mind:
Can the pencil of the draughtsman be any longer profitably employed upon nebulae as seen through the 6 foot reflector when photography, to say the least the least, follows so closely on his heels?
The metal mirrors making up the telescopes of the Rosse estate were possibly as good as they could be, but new technology made them living dinosaurs. In particular, the advent of much lighter silver on glass mirrors rendered the construction of large, observatory class reflectors much more easy to fashion, owing to their vastly reduced mass and higher reflectivity. In addition, glass substrates, with their lower thermal coefficients of expansion (and, to a lesser degree, their higher specific heat capacities) than the old speculum metals rendered them considerably less sensitive to small changes in temperature, allowing more stable images to be maintained in the course of a night’s work.
Lord Rosse passed away on August 30 1908 and with him all work with the Leviathan of Parsonstown ceased. With his brothers becoming the executors of his estate, the great telescope was dismantled because of growing concerns that it had become a working concern. In 1912, the 6 foot mirror was removed and despatched to the Science Museuem in London for preservation. The 36 inch was also left idle. Dr. Boeddicker, remained in the employ of the fifth Earl, though not it seems, in a scientific capacity. He was entrusted with gathering together the historical archives of the family. And when the First World War broke out in 1914, Boeddicker, a native of Germany, was considered an enemy of the state (which was still under British rule) and was forced to return to his own country. He died aged 84 in 1937, under Hitler’s Third Reich.
The next decade of Irish history proved very turbulent, with the result that the Rosse family had to leave the castle for extended periods of time. By the time the political climate settled down in the late 1920s, the great infrastructures that once boasted the largest telescopes on the face of God’s Earth were in a very sad state of delapidation, though according to Sir Charles Parson, the 36 inch was ‘nearly intact’ as late as 1927. That said, it’s whereabouts today is unknown.
A final twist in the story of the Leviathan occurred after a TV programme, lecture, and book by the late Sir Patrick Moore appeared on the great telescope in the 1970s. This resulted in a renewed interest in the 72-inch telescope, with the restoration of its wooden tube between 1971 and 1975, and soon it became a tourist attraction. But it was not before the 1990s that plans to actually rebuild the telescope came to fruition. In 1994, the retired structural engineer and amateur astronomer, Michael Tubridy, was commissioned to research and re-design the Rosse Leviathan. Unfortunately, the original plans were lost, and so it took a considerable amount of detective work which included re-examining the remains of the telescope, together with old observing logs and contemporary photographs taken by Mary Rosse, wife of the 3rd Earl. Reconstruction work lasted from early 1996 until the beginning of 1997. It had been planned to include a working mirror, but owing to budget constraints, this had to be left for a separate project.
The new mirror was installed in 1999. Unlike the speculum original, and in a historically respectful departure from modern aluminium- or silver-coated glass mirrors, the replica was cast from solid aluminium, thus acting as a compromise between authenticity and utility in astronomical observation.
The great technical achievements of the Rosse family, their friendship to the people of Ireland, as well as to the wider international astronomical community, will not easily be erased from memory. Once the brain and glory of all that was held dear in astronomical enquiry, their telescopes continue to be remembered in the mind’s eye as emblems of the indefatiguable spirit of the human imagination; to peer farther into space than anyone had ever seen before; to bring the heavenly creation closer to the earth, as well as to understand something more of its mysteries. And we’ve been doing that ever since.
References & Links
Mollan, C., William Parsons, 3rd Earl of Rosse: Astronomy and the Castle in Nineteenth-century Ireland (Royal Dublin Society – Science and Irish Culture), Manchester University Press, 2014.
Moore, P., The Astronomy of Birr Castle, Quack Books, 1992.
King, H.C., The History of the Telescope, Dover, 1955.
Ball, R.S., The Story of the Heavens, Casell, 1893.
Denning, W. F., Telescopic Work for Starlight Evenings (1891), HardPress Publishing, 2013.
Bell, L. The Telescope (1922), HardPress Publishing, 2013.
Read more about the telescopes and personalities that inspired four centuries of telescopic astronomy in my up and coming book, Astronomy Tales from the Golden Age.