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Description: | A primary Gregorian mirror of speculum metal. William Herschel made and used Gregorian telescopes before moving on to Newtonian and later Herschelian (to his own design) telescopes.
This mirror is without a cell and is lying loosely in a tin case with a cover. The general figure of mirror is very even from edge to centre, except for a fairly narrow and shallow zone of short focus just outside the central hole. From a zonal test it was found that the mirror is considerably over-corrected, as tested under a slightly rising temperature. A falling temperature would probably increase the over-correction still further.
AUDITED. .Negative Number D1968/1. F3362 is incorrect.
caption: disc, speculum metal | Publisher: | "http://collections.rmg.co.uk/" | Rights holder: | "Royal Museums Greenwich" | Subjects: | speculum metal mirrors Gregorian telescope A Catalogue of Instruments made and (or) used by Sir William Herschel as Preserved at Slough & examined ther in 1924 May & June A Peep into Herschel's Workshop | Source: | Royal Museums Greenwich | Identifier: | http://collections.rmg.co.uk/collections... | Go to resource |
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