Abstract
A LARGE telescope disk for the University of Michigan,has just been completed by Chance Brothers, Ltd., of Smethwick, Birmingham. Now that work is finished on the moulding and annealing of the disk, which is of dense flint optical glass, 25 inches in diameter and almost 4 inches at its thickest edge, it will be dispatched to the Perkin Elmer Corporation in the United States, where it will be ground and polished for use in the objective of a new Schmidt-type telescope now being built for the University of Michigan by the Warner Swasey Co. of Cleveland, Ohio. The sequence of operations necessary for the production of this disk occupied eight months. A special melting of glass of the required composition to give the necessary refractive index was rendered homogeneous by stirring and then cast into a large block weighing about half a ton. The surfaces of the block were polished to detect any portions containing defects. Finally, a portion weighing about 250 Ib. (approximately a quarter) was selected, heated to softening point and moulded to the required circular shape. The surfaces of the moulded disk were then polished for further inspection ; after which it was annealed in an electric furnace, this operation taking four weeks. Finally, the disk was tested in the Chance Laboratories, first on an interferometer to prove the perfection of optical homogeneity, and, finally, in polarized light to detect any abnormal mechanical stresses which might affect its performance. A second disk, similar to the one described, is also being manufactured for the Warner Swasey Co. It is of interest to note that Messrs. Chance Brothers are now celebrating the hundred and twinty-fifth anniversary of their foundation.
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25-Inch Telescope Disk for the University of Michigan. Nature 164, 1077 (1949). https://doi.org/10.1038/1641077a0
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DOI: https://doi.org/10.1038/1641077a0