During a recent trip to London, I paid a visit to the Science Museum. In the space gallery were the old favourites of the mock-up Lunar Module and various rockets and space vehicles. The one item
that really caught my eye however, was the first mirror that Willaim Herschel made for his great 40-foot telescope in 1785. This is a 36-inch mirror and is cast from Speculum metal. For nearly 60 years this was the largest telescope mirror in the World!
William Herschel’s 36″ Speculum mirror at the Science Museum, London, in 2008
Despite weighing half a ton the mirror was actually too thin and so Herschel decided to make a second, thicker mirror in 1789. In spite of its problems, this original mirror was often used whilst the new main mirror underwent repolishing. Using the 40-foot telescope, Herschel discovered two new moons of Saturn, Enceladus and Mimas.