This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
This moving show-window attraction can be simply and cheaply made. The things necessary are a small battery motor, a large horseshoe magnet and a large polished steel ball, perfectly true and round, such as used in bearings. The other materials usually can be found in any store. Procure some thick cardboard and cut two disks, 8 in. in diameter, and two disks, 7 1/2 in. in diameter. Glue these together to make the wheel A, the larger disks forming the flanges. Make a smaller wheel, B, the size of which will be governed by the speed of the motor used. The wheel A is mounted in a box to run with its surface close to the under side of the cover, which should be of a thin, stiff cardboard. The wheel B is mounted on an axle that runs in metal bearings. The magnet D is placed on the wheel A. The steel ball E is put on the thin cover of the box, and the magnet causes it to roll around as the wheel turns. The box inclosing the mechanical parts should be placed out of sight when used in a window. - Contributed by Clarence Guse, Spokane, Wash.
Ill: The Steel Ball is Caused to Roll Around on the Cover by the Moving Magnet