33.—Reversible perspective of a group of rings or of a tube.
Fig. 34.—Schröder’s reversible staircase.
In [Fig. 35] is a similar example. First one part will appear solid and the other an empty corner, then suddenly both are reversed. However, it is striking to note one half changes while the other remains unchanged, thus producing momentarily a rather peculiar figure consisting of two solids, for example, attached by necessarily warped surfaces.
Fig. 35.—Thiéry’s figure.