160. Mediums for Physical Effects are more espe-
cially fit to produce material phenomena, such as move-
ments of inert bodies, noises, &c. They may be divided
into optional mediums and involuntary mediums. (See
Part II., Chapters II. and IV.)
Optional Mediums are those who have a conscious-
ness of their power, and who produce the spirit phe-
nomena by the power of their will. This faculty,
though, as we have said, inherent in the human spe-
cies, is far from existing in all in the same degree; yet,
if there are few persons with whom it is absolutely null,
those who are capable of producing great effects, such
as the suspension of heavy bodies in space, aerial trans-
lation, and, above all, apparitions, are still more rare.
The most simple effects are those of rotation of an object,
rapping by the raising of the object, or even within its
substance. Without attaching primary importance to
these phenomena, we engage not to neglect them ; they
may give occasion to interesting observations and aid
conviction. But it is to be remarked that the faculty of
producing physical effects rarely exists with those who
have more perfect means of communication, as writing
and speaking. Generally, the faculty diminishes in one
sense in proportion as it develops in another.
