Annals of the Astrophysical Observatory of the Smithsonian Institution (1900)
Washington : Government printing office · leaf 351
Astrophysical Observatory Annals, Volume I. Plate XXXIa. … Spectrum Energy Curves of Welsbach and other Heated Mantles, from Bolographs with a 60° Rock-Salt Prism. Observations of S. P. Langley, with the assistance of C. G. Abbot.
Infrared spectra · Solar radiation
Internet Archive · Smithsonian Libraries · Public domain (published before 1931). Free to use for anything.
