A Newtonian primary mirror of speculum metal with a focal length of 1ft 6ins
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| Artwork | x cm ( x in) |
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A Newtonian primary mirror of speculum metal with a focal length of 1ft 6ins
A Newtonian primary mirror of speculum metal with a focal length of 1ft 6ins. The mirror is very thick for its diameter, especially in an annulus about the centre of the back. It is badly chipped at the edge, but the chip is mostly at the back and encroaches only a little onto the front surface. An attempt was made to test it by Foucault's method on 17 June 1924, but the focal length proved inconveniently short for the apparatus and no zonal test was carried out.
Sir William Herschel
- Image reference: F3380
- National Maritime Museum, Greenwich, London, Herschel Collection
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