Clairvoyance in space is of various kinds and degrees. Sometimes it
consists in the perception of super-physical phenomena--the
unfurling of a strange and wonderful land; and again it appears to
be a higher power of ordinary vision, a kind of seeing to which the
opacity of solids offers no impediment, or one involving spatial
distances too great and too impeded for normal physical vision to be
effective.

That clairvoyance which consists in the ability to perceive not
alone the superficies of things as ordinary vision perceives them,
but their interiors as well, is analogous to the power given by the
X-ray, by means of which, on a fluorescent screen, a man may behold
the beating of his own heart. But, if the reports of trained
clairvoyants are to be believed, there is this difference:
everything appears to them without the distortions due to perspective,
objects being seen as though they were inside and not outside of the
perceiving organ, or as though the observer were in the object
perceived; or in all places at the same time.

Our analogy makes all this intelligible. To the flat-man,
clairvoyance in space would consist in that power of perception
which we exercise in reference to his plane. From the third
dimension the boundaries of plane figures offer no impediment
to the view of their interiors, and they themselves in no way
impede our vision of surrounding objects. If we assume that
clairvoyance in space is the perception of the things of our world
from the region of the fourth dimension, the phenomena exactly
conform to the demands of our analogy. It is no more difficult
for a four-dimensional intelligence to understand the appearance
or disappearance of a body in a completely closed room, or the