photoelectric #3

wood, steel, glass, electrical equipment

A balance is mounted on the wall. At one end there is a photoelectric cell, at the other, a pair of propellers. The end with the propellers is heavier. As the balance falls to one side, a light aligns with the panel, causing the propellers to rotate and lift the heavy end. As the heavy end rises, the panel moves out of alignment, cutting the power supply and causing the balance to fall once again. The viewer is able to stop the cycle by turning off the light.

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