Last Updated: Aug 10, 2018     Views: 745

Photograph of George Otis Gleason taking measurements of 200” disk, Rakow Library bib no. 117727
Image: George Otis Gleason taking measurements of 200" disk while sitting inside center of disk, Rakow Research Library 117727.

Thank you for your question! You might want to read the following online articles in All About Glass on The Corning Museum of Glass website:

A colleague who had written the text for the Palomar exhibition at the Rakow Research Library at The Corning Museum of Glass, "Mirror to Discovery: The 200-Inch Disk and the Hale Reflecting Telescope at Palomar" (January 10 to October 30, 2011), shared this response:

"George Ellery Hale was the force behind the building of Palomar Observatory. Hale built the 60-inch reflecting telescope and then a 100-inch telescope which was installed at the Hooker Observatory, but he was convinced it was possible to build a 200-inch telescope. First, however, Hale had to find a company capable of creating such a large piece of glass. He began by commissioning the General Electric Company to make a disk from fused quartz. This effort failed to meet his requirements, however, and Hale began to look elsewhere. Corning Glass Works convinced Hale that its Pyrex glass could be used to produce a telescope mirror of the size that he desired. Pyrex was a strong glass with few imperfections. Hale decided to award the commission to Corning, and Dr. George V. McCauley, a physicist at that firm, was assigned the task of determining how such a disk could be made. McCauley began to make increasingly larger disks, using a process he had devised for casting huge pieces of glass. He created 26-, 30-, 60-, and 120-inch disks before finally preparing to produce the 200-inch disk. In 1934, two 200-inch disks were cast by Corning Glass Works under McCauley’s direction. The mold for the 200-inch disk was constructed in a manner identical to that employed for the 120-inch disk cast by Corning Glass Works in 1933. The 200-inch mold had 114 tall cores cemented to the bottom. Twenty-two of these cores broke loose during the first pouring, ruining the honeycomb design necessary to create a disk strong and yet light enough to be workable. Three ladles were used in the pouring of the 200-inch disk. As one ladle of glass was emptied into the mold, another was filled and trolleyed from the melting furnace to the mold. Each ladle held about 750 pounds of glass, although only a third of that glass made it into the mold during each pour. The rest was reintroduced into the furnace to be remelted. The crew poured about 100 ladles of glass during the operation. After the first disk failed, McCauley asked executives at Corning Glass Works if he could make another 200-inch disk. They agreed, and McCauley set out to improve the process and to produce a better disk. The second disk, a successful casting, was transported to California, where it was ground and polished over an 11-year span. Work on the disk had to be suspended during World War II, but after the war the disk was completed and installed in the Hale Telescope at Palomar Observatory. The first disk remained in Corning, where it was displayed in Pine Street Square (now known as Centerway) in its own custom-built museum. In 1951, the disk was moved to the site on which a new museum of glass and glass center were being constructed, across the Chemung River from downtown Corning. It was installed in the Corning Glass Center, where it was the first sight for visitors entering the complex. In 1999, the disk traveled again to the Glass Innovation Center in The Corning Museum of Glass where it remains."


For more information, we have lists of resources we can send, or you can look for these books at your local library:

Online Videos

You might also find the videos below from the Museum's YouTube channel of interest.

First: "Hear from Scott Kardel, the public affairs coordinator for the Palomar Observatory.... There are five telescopes used at Palomar, including the 200-inch Hale Telescope (the 'Big Eye')...."



Second: Rob Cassetti, Senior Director, Creative Services and Marketing at The Corning Museum of Glass, discusses the initial 200-inch disk, which has been displayed at the Museum since it opened.



Please do not hesitate to contact us in the future with your glass-related questions!





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