The most ambitious undertaking in the history of the National Bureau of Standards (NBS) 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 information on methods of making glass for a large telescope reflector--it was of course a trade secret—NBS borrowed on its own experience and began to experiment. It took several tries between 1924 and 1928 before a disk was successfully poured and cooled with cracking. [From: Measures for Progress by R.C. Cochrane, p. 274]. The images in this collection document the work to design and pour the disk.
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