Magic wheel
The magic wheel, or magnetic wheel is a wheel that continues to spin for a long time after being started, and is one of the earliest examples of an attempt at a perpetual motion machine. This device was invented in medieval Bavaria. It looked like a wagon wheel spinning on an axle, affixed to a base. The superstitious population of the time believed it spun by the power of magic.
The mechanism of the magic wheel used several large magnets (lodestones) affixed to the wheel's outside rim, like the seats of a Ferris wheel. Each magnet was backed by a lead plate "seat". An extra stationary magnet was affixed to the base. Each magnet on the wheel's rim was attracted to the magnet in the base on its downward approach, then prevented from turning over when the opposite pole of the magnet passed over in the wheel, thus being repelled upward. The magnets were not allowed to touch one another. This attraction-repulsion maintained inertia efficiently, similar to a flywheel, such that the wheel spun for a very long time and was thought supernatural by some.
Incorrectly deemed by some to be a perpetual motion machine, the magic wheel eventually comes to a stop because of frictional losses at the central bearing. Proponents of free energy devices have advanced the theory that the lead plating interrupts the magnetic attraction between the rim magnets and the stationary magnet in sequence, thus permitting the wheel to continue turning and bring the next rim magnet into position. However, the presence of lead dampens magnetic fields equally in any directions (as a magnet's field lines must stay continuous from pole to pole), and the symmetry of closed forces in the system means that no interaction between rim magnets and the stationary magnets could generate the net increase in energy necessary to keep the wheel rotating.
The magic wheel was an impressive invention for the Dark Ages, a time when even some European kings were illiterate. An early German woodcut depicts a magic wheel.