Measures for Progress: A History of the National Bureau of Standards

RESEARCH FOR INDUSTRY 275
Prof. Clifford C. Crump, director of the Perkins Observatory and Dr. Burgess examining
the Bureau's 69.5-inch telescope disk after an 8-inch hole had been drilled through its
center for mounting. The disk after polishing was set up in the observatory at
Ohio Wesleyan University.
If the most ambitious project of the optical glass section was the
telescope disk, perhaps one of its greatest pieces of craftsmanship was the
construction in 1926 of the Bureau's first standard of planeness. This stand-
ard of straightness, as well as planeness, in the form of highly polished disks
of clear fused quartz, was the work of John Clacey, a remarkable self-trained
hand craftsman of fine lenses who came to the Bureau in his 54th year back
in 1911 and worked with Michelson during the war. The disks he shaped
a decade and a half later, three in number in order to provide a self-checking
standard, proved when tested interferometrically to have an accuracy of
five-millionths of an inch. Aside from its application in testing the plane-
successful cast in 1934, the temperature was held at 1,2000 F. The mirror was then
cooled at the rate of 10 a day for 8 months. It was shipped to Palomar in 1936 to be
ground and polished, but interrupted by the war the work was not completed until
1947. Six and a half million dollars went into the making of the mirror. The Corning
Glass Center (Corning, N.Y., 1958), pp. 6, 8; Frederick A. White, American Industrial
Research Laboratories (Washington, D.C.: Public Affairs Press, 1961), pp. 47-48.