Color-vision and color blindness, a practical manual for railroad surgeons
A 1920 practical manual on color vision and color blindness by John Ellis Jennings, published in Philadelphia by F.A. Davis for railroad surgeons testing employees' sight. The plates are line diagrams: overlapping bell curves plotted across spectral letters R O Y G B V, and ray traces through lenses and screens, giving designers clean scientific curve charts and simple optical schematics with letter-labeled axes.
