This folding viewer for individual stereoscopic pictures has a cut-out between the lenses to accommodate the nose of the user. The original folding viewer was patented by J. F. Mascher of Philadelphia in March 1853 and was designed to hold stereoscopic portraits using the daguerreotype process. This was at the very end of the daguerreotype era, and originals are quite rare.Metal stereo viewer and many cards including stereoscopic photographs of crystal modals (Bragg's Crystal, Fluorspar, caesieum chloride, zinc-blende, iron pyrites, quartz, Tellurirumetc), and Dr Mullers Universal X-Ray Spectrograph. stereoscope, adam hilger, sir william bragg, w.i. bragg, dr muller, x-ray, crystal, spinel, bismuth, diamond structure, tartaric acid, naphthalene