Über den Helligkeitswert der Spektralfarben bei verschiedener absoluter Intensität
A German scientific monograph on colour science by Arthur König, printed in Hamburg in 1891, presenting measurements of how brightly spectral colours appear at different absolute intensities. The pictures are plotted graphs of luminosity curves across the spectrum, drawn as thin dashed and solid lines on ruled grids with wavelength labels, many printed sideways on the page. A designer could take from them the clean, precise line-and-grid style of early scientific charts and the smooth bell-shaped curves that map colour sensitivity.
