MARK THOMAS / SCIENCE PHOTO LIBRARY MARK THOMAS / SCIENCE PHOTO LIBRARY
Stick of different coloured wools used for testing people for colour blindness. The person being tested was shown a coloured piece of wool and had to pick the same colour from this selection. If colour-blind the person would not be able to pick the correct colour. This test was introduced by Dr William Thomson in 1880. Photographed at the Royal College of Ophthalmologists, London, UK.
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