| 摘要 |
A projector for projecting a movable spot of light onto a screen includes a pair of plates mounted adjacent and parallel to each other, each plate being opaque, apart from a straight slot. The slots cross one another at a crossing point defining an aperture which is transparent to light from a light source. The plates are mounted to be independently movable in such a way that the aperture is selectively displaceable thereby to allow controlled movement of the spot on the screen.
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