speculum mirror
noun [ C ] uk/ˈspek.jə.ləm ˌmɪr.ər/ us/ˈspek.jə.ləm ˌmɪr.ɚ/
（旧时望远镜中所使用的）铜锡合金反射镜
a type of mirror made from speculum metal (= a mixture of copper and tin) that was used in old telescopes (= devices for looking at stars and other things that are far away)
The Melbourne reflector was the last major telescope to be equipped with a speculum mirror. 墨尔本反射镜是最后一个装有铜锡合金反射镜的大型望远镜。
- More examples
- A speculum mirror will bend three times as much as a glass one because it will be three times as heavy.
- The largest ever speculum-mirror-based telescope was built by William Parsons.
- The radius of curvature of the speculum mirror was 6.55 metres.
- Lassell's 47-inch reflector, made in 1860, was the last large reflector with a speculum mirror.