polygonoscope

from The Century Dictionary.

• noun An instrument of the nature of the kaleidoscope, used to produce a great variety of geometrical patterns by the reflections from two mirrors supported in a case and connected by an adjustable hinge; specifically, a compact form of carpet-exhibitor for the multiple reproduction of a pattern.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun obsolete An arrangement of hinged mirrors for the production of multiple images of an object.