Stereo-Project Viewer by Demaria Lapierre, for viewing projected images in stereo. Works with all classic formats from 45 x 107 mm to 8.5 x 17 cm. This rare viewer was demonstrated at the Société Française de Photographie (S.F.P.) on 6 November 1903. See attached pdf file for instructions of how it works:
S.F.P. 6 Nov.1903