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Telescope mirror. Engraving of the mirror from a telescope built by the German-British astronomer William Herschel (1738-1822). The upper image is a cross-section of the mirror, showing its concave shape. The lower image shows the mirror bound around its edge by an iron hoop with handles. The mirror was completed in 1795 by Herschel and his sister, Caroline. It was 122 cm (48 inches) wide, 8.9 cm (3.5 inches) thick and weighed 960kg. The mirror was concave so that it would act as a lens and focus light. The telescope was 12.3 metres (40 feet) long. The eyepiece was at the top of this to avoid the loss of light caused by a secondary mirror. The telescope was dismantled in 1839.
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