The book Sound Picture Circuits, published in 1936 and authored by FINN (likely James J. Finn, editor of International Projectionist magazine), is an educational and instructional hardcover text focused on the technical aspects of early sound film projection systems. 
 
The book's content covers
- The use and maintenance of photo-electric cells (like the "Visitron" brand mentioned in related materials) used to read the optical sound tracks on film.
- The design and function of the associated vacuum-tube amplifier circuits common in 1930s audio and projection technology.
- Practical information relevant to projectionists and technicians for the installation, maintenance, and troubleshooting of commercial cinema sound equipment of that era. 
- The book is a historical technical covering history of cinema technology and early electronics