| Two bundles
of glass rods can be immersed, one at a time, into a liquid in a
glass tank. One bundle disappears completely while the other disappears
except for a single rod in the middle of the bundle. This is because
all of the rods (except for the one that remains visible) have the
same index of refraction as the liquid, so that light passes through
both the liquid and glass without bending and the rods become invisible.
The rod with a different index of refraction bends the light and
renders itself visible.