Abstract
ACCORDING to a Science Service report, the 200 in. mirror of the new Californian telescope will be made of a sort of pyrex glass and will be poured very shortly. It was at one time proposed to make the mirror of fused quartz, but a superior pyrex glass, which has a small temperature coefficient of expansion, has been developed for the purpose. The glass will be taken from the furnace at a temperature of 1,500° C. and poured at about 1,000° C. The cooling and annealing processes will occupy several months. The oven for the large reflector has already been used to make a 120 in. flat which will be required to test the larger mirror. Preliminary tests for strain have shown that this flat is superior to the excellent 60 in. mirror now used at Mount Wilson. The flat is perfectly clear and almost free from bubbles. The test flat will have the same type of construction as the big mirror, namely, a hexagonal system of ribs, which gives rigidity, and in which nineteen points of support will be provided. Ten supporting levers will be attached in ball bearings so that frictional and elastic distortions will be minimised. The holders will work in any position so that the mirrors can hang upside down if necessary.
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Pyrex Glass for the 200 in. Reflector. Nature 133, 412 (1934). https://doi.org/10.1038/133412a0
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DOI: https://doi.org/10.1038/133412a0