Annals of the Astrophysical Observatory of the Smithsonian Institution (1900)
Washington : Government printing office · leaf 60
Plate V. Annals Astrophysical Observatory, Volume III. … Observing Station on Mount Whitney. 1. Observer’s quarters, t t 2. Spectrobolometer. f Pyrheliometer. t Galvanometer room. Sky radiation bolometer.
Infrared spectra · Solar radiation
Internet Archive · Smithsonian Libraries · Public domain (published before 1931). Free to use for anything.
