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Description: | A Newtonian primary mirror of speculum metal with a focal length of 313.06cm.
The mirror is very smooth and regular but for a prominent zone of short focus whose radius was about 2/5 that of the whole mirror. There is also a small spot of short focus at the centre. The whole mirror appeared under the knife-edge to be of nearly spherical figure, or perhaps very slightly parabolic.
William Herschel, with help from his brother Alexander and his sister Caroline made a number of these mirrors to go in the telescopes they made to use and to sell. A mirror of this size and focal length would have been used in one of their 10ft telescopes.
AUDIT - object needs to be marked with its NAV number - three unnumbered parts. Part in KB1264 63C. Negative number:D1968/1.
caption: Newtonian primary mirror | Publisher: | "http://collections.rmg.co.uk/" | Rights holder: | "Royal Museums Greenwich" | Subjects: | speculum metal mirrors 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 Newtonian | Source: | Royal Museums Greenwich | Identifier: | http://collections.rmg.co.uk/collections... | Go to resource |
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