French Mystery Gravity Rolling Clock

France, circa 1920. This very unusual clock is never wound with a key, but does feature an entirely mechanical movement. The rolling clock receives its power from a counterweight inside the heavy brass case. The case slowly rolls down a delicately carved wooden plane, yet keeps the hand-painted porcelain dial upright all the time. At the end of the running period, simply replace the clock at the top of the plane, and it continues to run, without missing a beat.