It has the famous "Multi" gear: about 20 speeds by moving the lever on the other side of the bike. The back belt pulley contracts while the front pulley expands, keeping belt tension constant. The Rudge Multi ran from about 1912 - 1922, famously winning the Isle of Man Senior TT in 1914. This design, with the dropped tank, was based on the bike designed by Cyril Pullin that won that event.
Leon