Necker Cube: A Visual Illusion

When you stare at the wire frame model of a cube for a while, the cube seems to flip its orientation between two possible interpretations of the picture.

The only browser that currently runs Java applets is Firefox where, too, you have to make the site cut-the-knot.org trusted in the Java setup

What if applet does not run?

Discovered in 1832 by the Swiss chrystallographer L. A. Necker, this ambiguous picture now bears his name. The wireframe cube depicted in the orthographic projection, loses perspective clues that would otherwise help brain identify cube's orientation. Thus the wireframe figure could be perceived as representing two different 3d boxes. This one is similar to the Staircase illusion and the Shifting Cube illusion.

71231076