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| © National Maritime Museum, London |
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| Repro ID: H5522 |
| Description: This was one of five altazimuth instruments commissioned from Troughton and Simms for the British Transit of Venus expeditions of 1874. An altazimuth instrument is a telescope with scales and mounting that allow both local coordinates - the altitude and the azimuth - of a star to be measured without the need of any additional apparatus. The telescope and mount each have their own fitted wooden box. The telescope is made of brass and has a focal length of 22 inches (55 cm), a lens aperture of 2 inches (5 cm) , and an overall tube length of 10 inches (25 cm). The diameter of the setting circles is 16 inches (40 cm). In addition to the telescope and mount there are 2 eyepieces, 4 fine reading microscopes, 2 course reading microscopes, 2 12-inch (30 cm) diameter glass plates (1 broken), 2 enlarging lenses to read the altazimuth scale (1 missing) and 2 spirit levels. |
| Creator: Troughton & Simms |
| Date: 1870 |
| Credit line: National Maritime Museum, London | |
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