"Imperial Stereoscope Lithographed Advertising Tin Sign, 1900"
How far we've come since our ancestors marveled at mountain images, which they could slide into their cameras and adjust to their vision by sliding the photos... Nostalgia? Perhaps. A curiosity from the past, certainly. The Imperial advertising lithographed metal sign has been used countless times since 1900... I've found a website that discusses it in detail (https://vintageviewers.com/npg-stereo-viewers). My camera is in very good condition and comes with ten stereoscopic photos. 
Le Magazine de PROANTIC
TRÉSORS Magazine
Rivista Artiquariato