The Legacy of Yerkes Observatory

The Yerkes Observatory in the Village of Williams Bay, Wisconsin, on the shores of Geneva Lake in Walworth County, was completed in 1897. The observatory contains the largest lens-type telescope in the world, known as the Yerkes “Great Refractor”. It was the largest operating telescope of any type in the world from 1897 to 1908 and is housed inside a tower that is 112 feet high and 90 feet in diameter on the west end of the building. A barrel or telescope tube 64 feet in length holds two 40-inch diameter lenses at the front end – one convex in shape (the “crown glass”) the other concave (the “flint glass”) – at the proper distance to bring light to a perfect focus 63.51 feet (19,359 millimeters) at the back end. The lenses, which together weigh about 500 pounds, were cast in Paris, France by the optical glass manufacturer Mantois in the late 1880s. They were ground and polished by the famous American optical firm of Alvan Clark and Sons in Cambridge, Massachusetts, makers of many of the 19th century’s largest astronomical instruments worldwide including in the 26-inch United States Naval Observatory telescope in Washington DC and its identical twin at the Leander McCormick Observatory on the University of Virginia campus in Charlottesville, Virginia, the 24-inch Lowell Observatory refractor in Flagstaff, Arizona, and the 36-inch Lick Observatory refractor near San Jose, California.

The telescope is constructed entirely of steel and was built by the machine tool manufacturing company Warner & Swasey. It stands 65 feet in height from the base of the pier to the top of the German equatorial mounting, resting on a concrete and brick pedestal that is about 25 feet high. The estimated weight of the entire instrument is 82 tons. The telescope is accessed via the largest indoor elevator in the world – a movable floor, 75-feet in diameter and weighing 37-1/2 tons, that raises and lowers through a total distance of 26 feet using a counterweight system. The Great Refractor is still fully operational and delivers superb views of celestial objects. Active research work with the telescope ended in the 1980s. For about 25 years the telescope was used infrequently, being featured on exhibit for guided public tours and used for occasional special programs. From February 2016 until October 2018, when the observatory was temporarily closed by its former owner, The University of Chicago, it was used for scheduled, paid public observing programs. After refurbishment of the telescope and renovation of the 90-foot dome are completed in 2021, the Great Refractor will once again be the third largest telescope in the world available for public access.

Two operable, research-grade, mirror-type (reflecting) telescopes are located in separate towers on the east end of the Roman cross-shaped observatory building. A 24-inch diameter Boller and Chivens Cassegrain reflector, c. 1965, is housed in the north dome which is 26-feet in diameter. The south dome, 30 feet in diameter, houses a 41-inch Warner & Swasey Cassegrain reflector, c. 1968.

The Chicago millionaire traction magnate, Charles Tyson Yerkes, Jr., provided about $400,000 in funding between 1892 and 1897 to construct the Great Refractor and build the observatory that bears his name. He donated the facility to the University of Chicago in October 1897. The university owed Yerkes Observatory until May 1, 2020 when it and 50 acres of land were donated to the Yerkes Future Foundation, an independent, charitable, nonprofit organization that is currently raising funding to renovate the facility and reopen it to the public in 2021.

Yerkes Observatory, “the birthplace of modern astrophysics”, in Williams Bay, Wisconsin is the home of the 40-inch diameter “Great Refractor”, the world’s largest lens telescope, completed in 1897.  From 1897 to 1908 the Great Refractor was the largest astronomical telescope in the world.  It was succeeded in size by the 60-inch diameter reflecting (mirror-type) telescope – often called the “five foot telescope”, at the Mt. Wilson Observatory situated above Pasadena, California and affiliated with both the Carnegie Institute and the California Institute of Technology.

The refractor’s two lenses, one convex (the “crown glass”) and one concave (the “flint glass”), were cast in 1888 by the French company Para-Mantois – the successor to the firm of Charles Feil and Henri Guinand dating to the early part of the 19th century, and today known as Corning Specialty Glass located on the River Seine southeast of Paris.  The two lenses together weigh about 500 pounds (about 227 kilograms) and are 40-inches in diameter (1 meter).  The focal length of the telescope is 63.51 feet (19,359 millimeters).  The tube or barrel of the telescope is 64 feet long and weighs six tons.  The refractor stands 65 feet tall (about 20 meters) from the base of the pier (located under the elevator floor) to the top of the German Equatorial mount.  The entire telescope is estimated to weigh 82 tons.  The telescope tube and mounting are made of steel produced by the Carnegie Steelworks in Homestead (Pittsburgh), Pennsylvania.

The lenses, considered two of the finest ever produced for an astronomical telescope, were ground, figured and polished by the famous optical firm of Alvan Clark and Sons in Cambridge, Massachusetts.  Alvan Graham Clark, the last surviving member of the famous family of 19th century lens makers that began operation in the 1830s, was the chief optician who worked on the project, along with his assistant, Carl A. R. Lundin.  Over a 50-year period the Clarks fabricated lenses for most of the large American refracting telescopes still operating today, and thousands of smaller telescopes for universities and private individuals still in existence, operating and highly prized for their craftsmanship. The Clarks produced lenses for some of the most famous observatories including  Lick Observatory (University of California) near San Jose, California (36-inches), the United States Naval Observatory in Washington D.C and the Leander McCormick Observatory in Charlottesville, Virginia (the two telescopes are identical 26-inch refractors) the Lowell Observatory in Flagstaff, Arizona (24 inches), the Chamberlain Observatory in Denver, Colorado (20 inches) and the Dearborn Observatory (Northwestern University) in Evanston, Illinois (18.5 inches). The lenses for those telescopes, incidentally, were cast by Feil / Guinand / Mantois, one of only two fine producers of optical glass in the 19th century.  Alvan G. Clark died of a heart attack just three weeks after the Yerkes lenses were installed, which makes it that last true Clark refractor.  His company survived into the 20th century under Lundin and others when it was eventually purchased by the Perkin-Elmer Corporation, manufacturer of scientific equipment, and folded into its optical division.  In the 1980s, P-E’s opticians manufactured the mirror for the Hubble Space Telescope.

The two lenses were originally commissioned by a group of businessmen in southern California who were determined to erect the world’s largest telescope, coincidentally, on Mt. Wilson. No observatory existed there in the 19th century and there were no means available to reach the 5,500 foot high summit with large equipment until George Ellery Hale left Yerkes and began work on the Snow Solar Telescope on the mountain in 1903 – using his own money.  Their plan was to donate the instrument and facilities to the University of Southern California, and “lick the Lick” telescope, as the group liked to say, which was operating in northern California under management by the University of California.  Fresh off their successes in casting and figuring the Lick lenses, Mantois and Clark got to work on building the next big refractor. But the project hit a snag early on. Just after the lens blanks arrived in Cambridge from Paris, bad news soon followed. The California financiers lost the money they intended to use for funding the 40-inch refractor in a land speculation deal.  Mantois and Clark were on the hook for the cost of the lens blanks, estimated to be several tens of thousands of dollars at the time. For all practical purposes, the dream of building a big telescope in southern California was dead, at least for the foreseeable future.  The 40-inch project was shelved.

Nothing happened with the lens blanks for nearly four years. They laid unloved and unwanted in Alvan Graham Clark’s workshop. A chain of events, beginning in 1890, would eventually bring the 40-inch refractor project roaring back to life with a new owner – the University of Chicago- and a brand new, state-of-the-art observatory in the small community of Williams Bay on Geneva Lake in Walworth County Wisconsin.

First, the oil baron John D. Rockefeller announced an initial donation of $2 million to establish the new University of Chicago with land donated by the retail giant Marshall Field on what was then the city’s far south side, in Hyde Park.  The “old” university had gone into bankruptcy four years prior. A group of alumni and former trustees approached Rockefeller for help in getting the school running again.  The 1890 donation would be the first installment of an estimated total contribution of $40 million (that same donation would total at least $600 million today) given to the university by “the Titan” over the next 20 years.

Next, the trustees hired a theologian and linguist, William Rainey Harper, from Yale University to be the first president of the new institution.  Harper was just 35 years old when he was appointed to the school’s top post.  He was incredibly energetic, ambitious, and intelligent. Hailing from Ohio, Harper graduated from high school at the age of 10, earned his undergraduate degree at the age of 14 and his PhD just before his 19th birthday.  Upon his appointment as president and arriving in Chicago, Harper hit the ground running. He set to work on designing a world-class research university. He hired as many first-rate instructors in the natural and physical sciences, humanities, theology, and mathematics as his budgets would allow.  His nearly constant overspending would always be covered by Rockefeller. Following a campus plan and building designs by Chicago architect Henry Ives Cobb (who Charles Yerkes would hire a few years later to design the observatory) Harper and the trustees began erecting dormitories, lecture halls and laboratories.  The doors opened officially for classes on October 1, 1892.

Harper dreamed of developing an Ivy League-style educational and research institution in the Midwest.  Included in those plans was establishment of a first-rate physical sciences department, equipped with a decent sized telescope. It so happened that at the same time the university was forming, a young Chicagoan, George Ellery Hale, returned from the east coast with a degree in physics from the Massachusetts Institute of Technology.  His father, William Ellery Hale and his uncle, George Browne Hale, invented hydraulic elevators and founded the Hale Elevator Company (purchased by Otis Elevator Company in 1893) after the Civil War. The architect Louis Sullivan of Chicago credited William Hale as one of the two men most responsible for the development of the modern skyscraper.  The Hales were well-known, reputable industrialists and real estate developers in Chicago, philanthropic and very wealthy.  As a graduation gift to his son, William Hale built an observatory, designed by the famous architectural firm Burnham and Root of Chicago, and placed it in the backyard of the family mansion in fashionable Kenwood, a community wedged between the south side of Chicago and Hyde Park – and within a few miles of the new University of Chicago campus. After several attempts, William Rainey Harper convinced William Hale to donate the Kenwood Observatory, as it was known, with its 12-inch refractor (lenses fabricated by John A. Brashear of Pittsburgh, the other famous American optician of the era), to the university on the condition that George Ellery Hale be given a position on the faculty of the university.  Hale agreed to provide his son’s salary in the form of a monetary donation for each of the next five years.

Before classes began in October, George Ellery Hale traveled to Rochester, New York in the summer of 1892 to attend the annual meeting of the American Association for the Advancement of Science (AAAS).  By coincidence, Alvan Graham Clark was there too.  On a hot August night, sitting on the veranda of the hotel where the conference was being held, Hale heard Clark tell a small group gathered around him about the existence of the 40-inch lens blanks in Cambridge. Never one to let an opportunity pass him by, Hale rushed back to Chicago to tell the story to Harper, and the two men began a quest to find a donor to provide the funding to purchase the lenses, have Clark fabricate them and produce the worlds largest telescope.  They just needed $66,000.

It was Charles Hutchinson Jr., the son of one of Chicago’s founders, president of the Chicago Art Institute and godfather and confidant to George Ellery Hale who suggested to Hale and Harper that they approach Charles Tyson Yerkes for the money.  Yerkes, owner of two-thirds of Chicago’s street railway operations and one of Chicago’s most hated men, had indicated to his fellow members of the elite Union Club on Washington Square in Chicago that he might fund a project for the university if presented with just the right opportunity.  Funding the world’s largest telescope was just such a project.  Less than two weeks after classes at the new university began, Yerkes agreed in a meeting between himself, Harper, and Hale to purchase the lenses and build the observatory.  It was later recounted and published in Chicago newspapers that Yerkes told them to “make it the biggest and finest observatory in the world and send the bill to me” – words Yerkes would later regret.

Despite the economic collapse of 1893 which resulted in Yerkes losing a significant portion of his wealth – and causing him to seriously rethink his generous gift – and setbacks in construction of the building which didn’t begin until the spring of 1895, the Great Refractor saw first light in May 1897 under a 90-foot diameter dome.  It was all its builders hoped it would be, and more.  Today, the Great Refractor is still the largest lens telescope in the world.  It is also the third largest telescope in the world available for public viewing.