Lighthouses and Mercury Bearing
Some light apparatuses in lighthouses use a mercury bearing to reduce friction. This allows a faster rotation speed without powerful mechanisms. (In 1822 French physicist Augustin-Jean Fresnel developed the annular, or ring-shaped, lens. The light could now be flashed by rotating only the lens assembly while the light source itself remained stationary. By the 1890s, a tray of mercury was used as a bearing surface. This can be essential, as it allows the light to rotate faster, which can be quite helpful for a long list of reasons.)