polygonoscope

polygonoscope

(pəˈlɪgənəskəʊp)

[f. as polygon + Gr. -σκοπος, -ον viewing, he or that which views.]

An instrument on the principle of the kaleidoscope, consisting of two mirrors connected by a hinge, and capable of being set at any required angle, so as to produce an indefinite variety of patterns, which may be copied or photographed for artistic purposes.

in Knight Dict. Mech. Suppl.