The Mirror Stereoscope was primarily intended for viewing stereo illustrations mounted in books. The viewer was open on three sides, on the fourth side was a mirror to reflect light on to the subject, the divider running along the centre of the viewer was of ground glass. It could also be used to view conventional stereo cards by rotating two clips on the metal frame. The Mirror Stereoscope and the box-shaped 'Achromatic Stereoscope' by Beck were aimed at the upper end of the stereoscope market but sold in reasonably large numbers (serial numbers of over 3000 are known).