_The intrusion (as an apparition) of a person or thing into a
completely enclosed portion of three-space; or contrariwise, the
exit (as an evanishment) out of such a space_.
Because we lack the sense of four-dimensional space, we must here
have recourse to analogy, and assume three-dimensional space to be
the unsensed higher region encompassing a world of two dimensions,
To a hypothetical flat-man of a two-space, any portion of his plane
surrounded by an unbroken line would constitute an enclosure. Were
he confined within it, escape would be impossible by any means known
to him. Had he the ability to move in the third dimension, however,
he could rise, pass over the enclosing line without disturbing it,
and descend on the other side. The moment he forsook the plane he
would disappear from two-dimensional space. Such a disappearance
would constitute an occult phenomenon in a world of two dimensions.
Correspondingly, an evanishment from any three-dimensional
enclosure--such as a room with locked doors and windows--might be
effected by means of a movement in the fourth dimension. Because a
body would disappear from our perception the moment it forsook our
space, such a disappearance would be a mystery; it would constitute
an occult phenomenon. The thing would be no more mysterious, however,
to a consciousness embracing four dimensions within its ken, than
the transfer of an object from the inside to the outside of a plane
figure without crossing its linear boundary is mysterious to us.