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| Before electric lights were available, oil lamps such as this one were used for illumination in the laboratory. The motion of the mirror on the movable part of a galvanometer was observed either by looking with a telescope at a scale reflected in the mirror or by observing the movement of a spot of light reflected from the mirror onto a scale. This lamp and scale were used for that purpose--light from the lamp passed through a narrow slit to the mirror, and then it was reflected back onto the scale. |
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