The stereoscope / viewer is stamped on the metal hood - Exposition Universelle Internationale 1900 - H. C. WHITE Co. - and carved into the wooden base is PAT'D.OCT.15-95.
The cardholder is not included and the handle missing as well. There also appears to be solder to prevent rotation.
There is some wear to the metal hood that can be seen in the listing images. The wooden parts have a lovely aged patina. The felt surround on the headpiece has age related wear present.
The lenses need some cleaning.
The headpiece is a generous 5.2 inches / 13.1 cm wide and the whole unit is 13 inches / 33 cm long.
From Wikipedia
The Exposition Universelle of 1900 was a world's fair held in Paris, France, from 14 April to 12 November 1900, to celebrate the achievements of the past century and to accelerate development into the next. The style that was universally present in the Exposition was Art Nouveau. The fair, visited by nearly 50 million, displayed many machines, inventions, and architecture that are now nearly universally known, including the Grande Roue de Paris Ferris wheel, Russian nesting dolls, diesel engines, talking films, escalators, and the telegraphone (the first magnetic audio recorder).