Soon after William Herschel came to live at 19 New King Street (the home of the Herschel Museum of Astronomy), he built in this room, next to the kitchen, a furnace and smelting oven to make telescopic lenses. Stockpiles of horse dung (for making moulds) would have been stored in the surrounding vaults – one of which now forms the Star Vault Astronomy Auditorium.
Fortunately for William, his workshop at 19 New King Street was a room with two exits. Caroline Herschel records in her diary a potentially fatal event taking place in this room, involving William and Alexander (another Herschel sibling). While the brothers tried to pour 538 pounds of speculum metal into a mould made of horse dung (a method of casting still used today to make church bells), an explosive mishap occurred. Caroline noted: ‘Both my brothers… were obliged to run out of opposite doors, for the stone flooring flew about in all directions as high as the ceiling.’ Flagstones shattered by this molten spillage are still visible.
There are many fascinating objects in this room. These include a mould made of horse dung and plaster, into which molten metal was poured to make telescopic mirrors. There is also a replica of William’s parabolic mirror polishing machine, which visitors are invited to handle. (The original device is at the Science Museum in London. The model was created with funding from the Royal Commission of the Exhibition of 1851 and the Ernest Cook Trust.)