Standards of form and color-vision required in railway service
A 1897 paper by ophthalmologist Charles H. Williams, read to the American Ophthalmological Society, setting out the eye tests and colour-vision standards required of railway workers. Its three plates are photographs of an apparatus with a wooden disc and vertical board carrying a dark lens or coloured-glass mount, and a wheel of round openings with a central pointer used for testing. The photographs are plain, evenly lit and greyscale, with a flat ground and no ornament, so a designer could borrow their stark geometric layout of circle, bar and upright for a minimalist diagram.
