Spectrum lines as light sources in polariscopic measurements
A 1906 technical report by Frederick Bates, issued by the National Bureau of Standards in Washington for physicists and instrument makers working on polarimetry and spectral light sources. The plates are line diagrams of angles and ray paths lettered with Greek symbols, plus a reproduced spectrogram showing black bands cut by white gaps over a wavelength scale, useful as scientific line work and as high-contrast bar patterns.
