Lettering on a show-window sign will alternately appear and disappear when light is projected on it through this simple color wheel. To produce this effect, a four-spoke wheel is cut from plywood or gardpressed board and grooved around the rim for a belt. Then pieces of red and green Cellophane are glued to it, with the colors alternating so that pieces of the same color are on opposite sides of the wheel. Next, the sign is lettered with red and green paint, alternating he color of the lines of letters. When the light shines through Cellophane of the same color as that of the lettering, this lettering will become invisible. But lettering painted in the other color will be plainly seen. The wheel is mounted on a support in front of a spotlight, and is rotated by a belt running over the pulley of a small motor. This should have a variable-speed control so that the wheel will rotate slowly enough to allow the lettering on the sign to be read easily.
Ken Murray, Baltimore, Md.
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