The Gaumont Stéréodrome is a well designed and robust stereoscope for 6x13cm glass stereoviews, manufactured by the Societé des Etablissements Gaumont from Paris.

Léon Ernest Gaumont (1864–1946) was a French industrialist and pioneer of the motion picture industry. He worked at the Comptoir Général de Photographie from 1893 and acquired the business two years later. It was the start of L. Gaumont et Cie with the flower “Marguerite” as company logo.
Gaumont’s company sold camera equipment and film, but in 1897 they also began making short films. The business expanded and within a few years, the company ranked second only to Pathé Frères in the field of French Cinema. Léon Gaumont had built one of the most important film companies in cinema history before he retired in 1930. His company is the first and oldest film company in the world and still exists today.

Advertisement in La Revue Française de Photographie from October 1925
The Societé des Etablissements Gaumont was founded in 1906 to handle film production and distribution and it operated a chain of movie theaters. This company distributed also stereo cameras and stereoscopes. Their products were of high quality and it was a big competitor to Jules Richard.
The Stéréodrome design was patented in 1903[1] and the model in this post is for viewing 6x13cm glass stereoviews but there were also models available for the 45x107mm and 8,5x17cm format[2]. The device is well designed with a heavy duty and reliable construction. The various doors and flaps are fitted with metal sliding locks. The front panel contains a metal plate with Societé des Etablissements Gaumont Paris and the serial number 2347.
The lenses can be focussed and the distance between the lenses is adjustable. The bakelite slide tray can contain 20 slides. To display the images one by one, a crank is moved back and forth. The slide trays have a finger grip to help removing the tray from the device. It can also be used to navigate to a specific slide when the device is put into free position by shifting the small knob at the front to the right. Caution is needed here because the tray is forcibly pulled into the device if the knob is inadvertently moved to the right. Personally I don’t find this very user-friendly. It’s also possible to navigate between images by pulling down the knob of the index which is attached to the slide rail by a woven tape.

The back of the stereo viewer does not contain the usual frosted glass, but a flap that can be opened and which has a mirror on the inside. The frosted glass that illuminates the slides is mounted inside the device and the mirror provides extra light. The top can be folded up so that an optional projection lantern can be attached.
References
- Gaumont & Cie. Appareil perfectionné pour regarder et exhiber des vues et images photographiques ou autres, stéréoscopiques ou simples, rangées dans des magasins-classeurs, patent FR332006, 12 May 1903 – via: data.inpi.fr
- Catalogue général, Gaumont, 1 April 1924