William and Caroline Herschel's Telescope

On Sept. 9, 1839, the English polymath, John Herschel (1792-1871), took a glass plate photograph of the so-called 40-foot reflecting telescope that had been made in the late 1780s by his father and his aunt, William and Caroline Herschel, and erected on the grounds of the family home at Slough. The heart of this great instrument was a 48-inch primary mirror with a 40-foot focal length. This copy of that famous image was produced in 1890. The wood used to make the frame came from the telescope mount.