Magnetic wheel toy
The plastic wheel has a magnetic axle which allows it to roll along above and below the steel rails, now brown with rust in this example. When the rails are held just off the horizontal and the wheel placed on top, as in the first image, the wheel rolls along and when it gets to the end it rolls round the curve and, with care from the operator, remains attached as it rolls along underneath the rail, because it held in place by magnetism. By gently altering the angle of the rails it is possible to keep the wheel rolling along until it completes the circuit and starts again. A skilled operator can keep the wheel spinning round and round for a long time.