The Earl of Rosse's Leviathan Telescope
A Kenyon physicist explores a nineteenth-century scientific marvel with a Kenyon connection
by Thomas B. Greenslade Jr.
In early December 1987, William Brendan Parsons, the Seventh Earl of Rosse, gave a Common Hour talk in Rosse Hall on the Kenyon campus about "The Earls and Countesses of Rosse." The earl, a slender man with lilting Anglo-Irish speech, showed slides of his ancestors and their home, Birr Castle, and two great scientific achievements of the Parsons family: the "Great Leviathan" telescope of the third earl, and the steam turbine of Charles Parsons, the third earl's youngest son. I chatted with him about the telescope, and he invited me to visit Birr and see it in person.
Fortunately, I delayed my visit for ten years, by which time the telescope had been restored. My visit, during the first days of June 1998, was supported by the College's Faculty Development Fund.
The town of Birr, located seventy miles southwest of Dublin, sits in the geographic center of the combined Irish Republic and Northern Ireland. Rain fell almost every day my wife, Sonia, and I were in Ireland, but Birr greeted us with hail, which knocked inch-sized bits of moss off the roofs. As we walked past the Georgian houses of the town, the moss on the sidewalks resembled small, furry animals.
The Rosse demesne itself is separated from the streets of Birr by a fifteen-foot stone wall, high even by Irish standards. Once through the gates, we bore to the left and suddenly the stone walls of the telescope appeared through a gap in the trees. It was immense! My photographic instinct merged with my profession as an historian of Victorian science, and, equipped with four cameras, I stalked the "Leviathan."
The Rosse family member most familiar to Kenyon people is Jane, Dowager Countess of Rosse, who sent £200 to Philander Chase for his new seminary and later contributed an additional £100 for his personal use. Her contributions to Bishop Chase's new seminary were the largest he received, and we might ponder why we do not give our affection to Rosse College, perhaps located in Kenyon, Ohio. Her portrait in the foyer of Rosse Hall is labeled "Lady Jane King, who became the Right Honorable Dowager Countess of Rosse, Died 1836"; her husband, Sir Lawrence Parsons, was the first Earl of Rosse. William Parsons, third Earl of Rosse, was descended from the half brother of the first earl. I discovered his statue, with his life dates of 1800 to 1867 on the base, standing opposite our bed-and-breakfast on an avenue of classic houses near the center of Birr.
William Parsons graduated with first-class honors in mathematics from Magdalen College at Oxford University in 1822. He had a considerable career in politics, serving in Parliament from 1821 to 1834 and as the lord lieutenant of County Offaly, where Birr (once known as Parsonstown) is located. During the Potato Famine in the second half of the eighteen forties, Parsons was an enlightened landlord, remitting almost all of his Irish rents for the relief of his tenants. In 1841, he succeeded his father as the third Earl of Rosse.
At the same time, Parsons was doing important work on telescope design. His work with large telescopes included devising solutions to a whole succession of engineering problems--and carrying them out on the Birr Castle grounds with local labor. The funds for the telescope were provided by his wife, Mary, Countess of Rosse, who was an heiress from Yorkshire. And there were interesting spin-offs: because a foundry had been developed to cast the mirrors and other telescope parts, the coat of arms on the castle gatehouse was cast locally under the direction of Lady Rosse, including the two leopards on the sides, painted white with black spots.
To appreciate William Parsons's work, we need to turn briefly to some basic optics. We are all familiar with the use of binoculars. With their aid, we make objects appear closer; within limits, we usually want to use the largest possible magnification. The astronomer has a different problem. Astronomical objects are faint, and the astronomical telescope must gather as much light as possible to form a bright image. This image is then scanned with an eyepiece, which is a sophisticated version of the hand magnifier we use to make print in a book look larger.
There are two ways to gather light: the lens and the mirror. The forty-inch objective for the Yerkes telescope, put into use at the beginning of this century, is the largest lens ever made. Telescope lenses are actually two lenses mounted almost touching each other; making them requires that four surfaces must be ground and polished into the shape of the sphere. The reflecting telescope requires only one surface be ground into a concave shape. Today, all of the large telescopes of over forty inches are of the reflecting design.
Parsons was interested in nebulae, astronomical objects that appear to be cloud-like, as contrasted to the bright stars. Nebulae are very faint, and today we make long photographic exposures to intensify the effect of their light. In 1845, however, photographic science was still in its infancy, so Parsons had to rely on what he could observe with his eye, making hand-drawn copies of what he saw. Quite reasonably, he opted for a reflecting telescope that would gather the greatest amount of light with the least grinding. His first telescope, in 1840, was a reflector with a mirror three feet in diameter, and five years later he made the six-foot mirror.
Today, we cast telescope mirror blanks of glass, with small ones being solid and large ones having honeycomb cells on the back to decrease the weight. The reflecting surface is a thin film of aluminum, evaporated in a vacuum from electrically heated filaments. William Parsons did not have this technology, and his mirrors were made of a bronze alloy (speculum metal). To make the blank for the six-foot mirror, about four tons of metal were melted in three huge crucibles, with two thousand cubic feet of peat used as fuel. The mirror blank was cooled very slowly over a period of six to sixteen weeks to prevent cracking; if it had been cooled rapidly, tremendous stresses would have been built up between the cool exterior and the hot interior.
The mirror blank then needed to be ground to the required concave shape. This was done with a convex tool, essentially a disk covered with small squares of iron. A water slurry of various grinding powders, starting with coarse and ending up with very fine, was placed on the surface of the horizontal mirror blank. The tool was lowered onto the mirror and moved back and forth while the mirror was rotated about its axis. This produced a spherical surface, which was then altered to the necessary parabolic shape by an adjustment of the polishing machine.
The mirror was mounted in a tube fifty-eight feet long, eight feet in diameter in the middle and tapering to seven feet at the ends. The wooden tube, built by local coopers, had the form and construction of a very long barrel. Unlike modern telescopes, which are pivoted about the balance point of the tube and mirror, the Rosse telescope was pivoted at one end on a universal joint. This meant that strong chains and massive counterbalances had to be used to point the telescope to various points in the sky. To resist the resulting large forces, the tube was supported between two stone walls, seventy feet long and fifty feet high, with gothic arches in one side. In the nineteenth century, the outside portions of the walls were covered with ivy.
In the front view of the telescope, the circular rail used to guide the telescope up and down can be seen on the inside of the right-hand wall. In the other photograph the wooden braces and the rigging used to elevate the telescope can be seen, including one of the two large, cast-iron counterweights. The telescope faces south, and it can be brought down close to the southern horizon. In the other direction, the tube can be tilted about five degrees north of the vertical. The tube can be moved about ten degrees on either side toward the side walls. The rotation of the earth also brings different astronomical fields into view. All told, about 82 percent of the sky visible in central Ireland can be observed.
Modern large telescopes live inside domes, but the six-foot telescope and its observer were completely in the open. When the tube was at a small angle to the ground, the observer stood in the small cage to the left of the end of the tube. This ran on rails atop a gantry that could be lifted up and down, permitting the earl or one of his assistants to look through the eyepieces just visible at the end of the tube on the left-hand side. The right-hand side of the cage has a drawing board on one side; from its placement we can infer that the third earl was right-handed. At higher elevations, the curving gantry on top of the left-hand wall could be moved in and out, and the observer moved up and down the steps. Observing while perched sixty feet above a dark chasm must have been rather frightening at first. The constant movements of the telescope tube and the gantry as an object was tracked were accomplished by a team of five men, who turned windlasses in response to shouted commands.
Unfortunately, Birr is not a good place for a telescope. Over the course of a year, the viewing is good one night out of seven, and the good nights are concentrated in the autumn. The soft, damp Irish air made the mirror tarnish rapidly, requiring frequent repolishing. With two mirrors, a fresh reflecting surface could always be ready. When the time came to reload, the four-ton mirror was lifted off the telescope and onto a small railway flatcar. This was winched up to ground level on a set of rails, pushed onto a turntable, and then run off at right angles.
The year 1845 was a bad one to start a scientific enterprise in Ireland. The Potato Famine and the accompanying unrest occupied much of William Parsons's time. Thus, the Leviathan was not put into regular use until 1848. Contemporary astronomers agreed that it worked close to its theoretical limits, and the drawings of deep sky objects made by the third earl were widely used.
The fourth earl, Laurence Parsons (1840-1908), carried on his father's work, but was he best known for his research on radiant heat from the moon. The use of the Great Telescope had gradually come to an end in the late 1880s. In 1912, one of the mirrors was presented to the Science Museum in London, where it is currently on display, still resting on the small flatcar used to trundle it about for repolishing. Unfortunately, the surface is covered with a circle of glass, and I could not see much of it. The second mirror has disappeared, as well as the entire three-foot telescope. The rest of the telescope was then left to rust and decay, and plants grew on the top of the stone side walls.
But this was not the end of the telescope. Over the past ten years, it has been faithfully reconstructed. Ninety percent of the wood in the tube was replaced, the ironwork was refurbished and replaced, and electric motors were fitted to replace the exertions of the men who turned the cranks. The operation of the telescope is now demonstrated twice a day, with a computer controlling the various movements of the tube and the gantries. Toward the end of 1998, a new mirror was fitted. This is of aluminum, overcoated with a thin film of nickel and weighing only one ton. To let many people view the live image, a television camera replaces the eye of the single observer.
Two other members of the Parsons family deserve special mention. The brother of the fourth earl, Sir Charles Parsons (1854-1931), had a strong engineering bent; in 1884, he patented the steam turbine. This has had a major influence on modern life. All large ships today are powered by steam turbines, the descendant of his ship, the Turbinia, which, at the naval review held in 1897 to celebrate the diamond jubilee of Queen Victoria, literally ran circles around the fleet. The original application of the turbine was electric-power generation, and almost all electric power produced today comes from dynamos powered by steam turbines.
William Parsons's wife, Mary, Countess of Rosse, was an accomplished photographer, using the paper negative process developed by William Henry Fox Talbot in 1839. The third earl corresponded with Fox Talbot in 1852, seeking advice on astronomical photography, and within a couple of years his wife was producing views of the castle grounds and the telescope. These, as well as a number of photographs of family groups, have fortunately been preserved, and they show her to have had a good photographer's eye. I now have a reproduction of one of her pictures of the Leviathan telescope hanging on a wall of my house in Gambier.
Professor of Physics Tom Greenslade, a member of the Kenyon faculty since 1964, is a graduate of Amherst College with a doctorate from Rutgers University. He is the son of the late Mary M. Greenslade and Thomas B. Greenslade '31, the College's long-time archivist. Greenslade says he considers this article his "report to the Kenyon community" on the use to which he put his Faculty Development Grant.
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