The theory of spectra and atomic constitution;
Three essays by Niels Bohr on spectra and atomic structure, translated and issued by Cambridge University Press in 1922 for physicists and advanced students. The figures are line diagrams: electron transitions plotted as filled dots joined by straight and dotted lines against lettered energy levels, plus a bracketed table of the elements by atomic number, useful as sparse technical schematics and node-and-line motifs.
