SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Mechanical colour test. At upper left is the card used to record the result of the test. At centre left is a disc with colours on it. At centre is the hand-operated testing wheel itself, with a spinning top at top left and a disc with a radial slot at lower right. Artwork from the 15th volume (first period of 1895) of the French popular science weekly 'La Science Illustree'.
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