Grease Spot Photometer
A spot leading to enlightening insights.
What does the grease spot on the paper between the two lamps tell us? The grease-spot photometer was originally developed to compare electric light with candlelight. A brilliant trick!
If both lamps illuminate the paper equally from both sides, the grease spot isn’t visible. By mounting a rotating slotted disc in front of the left lamp, that lamp’s brightness on the paper decreases, making the grease spot visible.
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