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Newtonian primary mirror
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.
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.
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Object Details
| ID: | AST0808 |
|---|---|
| Collection: | Astronomical and navigational instruments |
| Type: | Newtonian primary mirror |
| Display location: | Not on display |
| Creator: | Herschel, William |
| Date made: | circa 1800 |
| Credit: | National Maritime Museum, Greenwich, London, Herschel Collection |
| Measurements: | Overall: 60 mm; Diameter: 224.79 mm |