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

274 THE TIDE OF COMMERCE AND INDUSTRY (1920-30)
changeable manufactures. Yet not until the very end of the decade was
there sufficient general acceptance to warrant extending this line of research
at the
Because of the technical difficulties, relatively small market for the
products, and ease of obtaining an adequate supply from Europe, efforts
to turn over to industry the making of optical glass met with little response.161
To assure sufficient glass for scientific purposes, the optical plant behind
the Industrial building continued its operations with annual appropriations
from Congress. Besides its research in optical and other types of glass for
the industry, the Bureau yearly melted approximately 30,000 pounds of
optical glass for the production of optical blanks, most of them going to the
military services. Allowing for wastage and imperfections, the yield of
serviceable glass from this weight of melt approximated 20 percent or 6,000
pounds.
The most ambitious undertaking in the history of the Bureau glass
plant was its casting of a 69.5.inch disk for the mirror of a large reflecting
telescope. At the time there were not more than 10 optical glass plants in
the world, all abroad, capable of making such a disk. The two largest in this
country, the 40-inch at the Yerkes Observatory and the 100-inch at Mount
Wilson, had both come from Europe. Challenged by the lack of informa-
tion on methods of making glass for a large telescope reflector—it was of
course a trade secret—the Bureau borrowed on its own experience and began
to experiment.
The first great disk was poured in 1924. It cracked during cooling.
So did the next three. Trying still another method, the Bureau cast a fifth
one in May 1927. Cooled in the first weeks at the rate of only 10 per day
and at no time more than 100 per day, in January 1928 the great disk, some
10.5 inches thick and weighing 3,800 pounds, was pronounced a success.
Polished and silvered elsewhere, the mirror was subsequently presented to
the Perkins Observatory at Ohio Wesleyan University.'62
M89, "Report of the National Screw Thread Commission" (rev. ed., 1928). The
Commission was placed on a permanent basis by Congress in 1926, abolished as an
economy measure by Executive order in 1933, and reestablished as an agency of the War,
Navy, and Commerce Departments in 1939.
in Of the firms that began making optical glass during World War I, all but Bausch &
Lomb ceased production with the armistice. Hearings * * * 1922 (Dec. 20, 1920),
p. 1248.
182NBS Annual Report 1927, p. 23; Annual Report 1928, p. 21; RP97, "Making the
glass disk for a 70-inch telescope reflector" (Finn, 1929) ; Harlan T. Stetson, "Optical
tests of the 69-inch Perkins Observatory reflector," J. Opt. Soc. Am. 23, 293 (1933)
conversation with Clarence H. Hahner, May 20, 1963.
Prior to the casting of the 200-inch mirror for the Hale telescope at Palomar, the largest
disk the Corning Glass Works had attempted was 30 inches. With the Bureau experience
as guide, work on the 200-inch, 15-ton disk began in 1931. For 2 months after the