esis of Direct Physical Action._--This supposes that the
molecular changes in one brain, accompanying thought or emotion, set
certain ether vibrations in motion, which are caught up by another
brain, sensitive enough to receive them, or attuned to the proper
degree. This theory is one which appeals to most persons, though it is
open to the criticisms before raised. Nevertheless, it _may_ be true;
and if so, its law ought one day to be discovered. There is here also a
field for legitimate scientific research.

5. _The Idea of a Universal Fluid._--This is the theory held to by the
majority of mystics and occultists. There is supposed to exist a sort of
fluidic intermediary between mind and mind, which acts as the means for
thought transmission, and it is upon this that all thought is impressed.
It acts as a sort of mirror, which reflects the thoughts of all living
persons, just as a material mirror might reflect material objects. In
such a case, the thought is really _made objective_ and is perceived by
the subject in a sort of clairvoyant manner. I do not feel competent to
pronounce upon this hypothesis in the present embryonic state of
psychical science.

6. _The Theory of Spiritual Intermediaries._--This is the theory that
our thoughts are read by some purely "spiritual" process, by "spirits,"
who convey this thought to another individual and impress him in some
psychical manner directly. They thus act as carrier-pigeons between mind
and mind. To this theory it may be replied, as Professor Flournoy has
replied in his _Spiritism and Psychology_, that it represents the grave
methodological defect of multiplying causes without necessity; by
postulating spirits and importing them into the problem when they are
not wanted. It would be better to seek an explanation elsewhere.

7. _The Psycho-Physical Theory._--This theory supposes that all thought
is accompanied by nervous undulations, which are carried to the surface
of the body, there setting the ether in vibration; and this, in turn,
impinges upon the periphery of another person, particularly sensitive to
receive them, and by him re-transformed into nervous currents--into
thought! Such a theory completely fails to take into account those cases
of long-distance telepathy, of which so many have now been collected;
and in other ways is very defective.

8. Assuming all the above theories to be insufficient, we now come to:

_The Elements of a Scientific Explanation_