of
disintegration, so does the other that of materialization; and just as
in the former case a continued effort of will is necessary to prevent
the object from resuming its original form, so in exactly the same way
in the latter phenomenon a continued effort is necessary to prevent
the materialized matter from relapsing into the etheric condition. In
the materializations seen at an ordinary _seance_, such matter as may
be required is borrowed as far as possible from the medium's etheric
double--an operation which is prejudicial to his health, and also
undesirable in various other ways; and this explains the fact that the
materialized form is usually strictly confined to the immediate
neighbourhood of the medium, and is subject to an attraction which is
constantly drawing it back to the body from which it came, so that if
kept away from the medium too long the figure collapses, and the
matter which composed it, returning to the etheric condition, rushes
back instantly to its source.

[Sidenote: Why Darkness is required.]

[Sidenote: Spirit Photographs.]

The reason why the beings directing a _seance_ find it easier to
operate in darkness or in very subdued light will now be manifest,
since their power would usually be insufficient to hold together a
materialized form or even a "spirit hand" for more than a very few
seconds amidst the intense vibrations set up by brilliant light. The
_habitues_ of _seances_ will no doubt have noticed that
materializations are of three kinds:--First, those which are tangible
but not visible; second, those which are visible but not tangible; and
third, those which are both visible and tangible. To the first kind,
which is much the most common, belong the invisible spirit hands which
so frequently stroke the faces of the sitters or carry small objects
about the room, and the vocal organs from which the "direct voice"
proceeds. In this case, an order of matter is being used which can
neither reflect nor obstruct light, but which is capable under certain
conditions of setting up vibrations in the atmosphere which affect us
as sound. A variation of this class is that kind of partial
materialization which, though incapable of reflecting any light that
we can see, is yet able to affect some of the ultra-violet rays, and
can therefore make a more or less definite impression upon the camera,
and so provide us with what are known as "spirit photographs". When
there is not sufficient power avail