Rare antyique patented changing back for Eureka Focal Plane Detective Hand Camera made by Rouch & Co., London. 

See photos for small defects like the dark slide does work but the top tab has been broken off, but the metal stopper is intact so will keep the dark slide in place. I haven't got much of an idea how this changing back worked so bought as seen. Please ask if any questions. The leaver on the box works, as does the release button to open the box. The inside measurement of the box is 12.2cm x 16.8cm.