A coin operated stereoscope with a nameplate of La Stéréoscopie Universelle, one of the largest publishers of World War I stereoviews in France. The stereoscope is manufactured by Mattey[1]. It’s a simple revolving stereoscope with lenses that cannot be focused and the distance between the lenses is not adjustable. What makes this device special is that it’s a coin operated stereoscope. The viewer is opened by removing the front panel with a key. The mechanism consists of an iron belt with slide holders in which 28 glass stereoviews of 45x107mm can be placed, an unusual number. With most revolving viewers, the slides must be placed by opening the lid at the top. With this device it’s done by removing the front panel and that makes placing slides a lot easier.

The mechanism is in locking position by default and it’s unlocked by inserting a coin via the top lid. The slides can be viewed one-by-one by rotating the knob on the right side. One slide holder has an arm and when all slides are rotated, the arm releases the coin which falls to the bottom and it locks the device. A metal spring supports locking and unlocking the mechanism. This viewer is in working condition, although the spring needed some minor adjustment.
The mechanism and holders for the glass slides are robust, indicating that this stereoscope is intended for heavy-duty use. La Stéréoscopie Universelle probably used these viewers during exhibitions and in showrooms to promote and sell their stereoview collections.


References
- Stereoscopes, Stéréscopes A. Mattey, 1936, p. 46