Egeler, C. E. (1921). Condenser Lenses for Theater Motion Picture Equipments. Advance Copy, May 9, 1921, no other publication information is available.
Printouts of catalog records for two other Egeler publications:
Archives and Special Collections, 622.47 Eg21i 1938, Illumination of mines and mining operations.
Archives and Special Collections, 621.326 G28, Bulletin / Engineering Department, National Lamp Works of General Electric Co.