[34] A Greek philosopher to whom change of spatial configuration,
pressure, and percussion were probably the only natural processes of
which he had any intimate knowledge, thought out the atomistic theory.
This theory we retain to-day, though it be in a modified form. And in
fact natural phenomena really do exist that act _as if_ the pressure
and impact of very small particles were involved in their production
(the dynamical theory of gases), phenomena that admit therefore by this
conception of being more clearly viewed. However, this conception, like
that of caloric, possesses value only in certain fields. We know to-day
that pressure and impact are by no means simpler phenomena than are for
example the phenomena of gravitation. The contention that in physics
everything can be reduced to the motion of smallest particles is, taken
at its best, a more than improper draft on the future. Utterances of this
kind afford no assistance to the solution of burning special questions,
but only confound, and have about the same explanatory value as the
utterances of the late physical philosophy of Oken which prescribe for
example with the greatest ease the course of the creation of the world by
a division of zero-quantities into _+a_ and _-a_ (0 = _+a_ _-a_).
The motion of a _single_ body as a totality does indeed appear simpler
at first glance than any other process, and this is the justification
of attempts at a _physical_ monadic theory. The thoughts of a _single_
man are connected together; the thoughts of two different men are not.
How can the processes of the different parts of the brain of one man be
connected? In order to make the connection very intimate, we collect
everything which requires to be psychically connected in _a single_
point, although the connection is not explained by this procedure. Thus
the psychological monadic theory is created on the basis of a motive and
of an illusion similar to that on which the physical rests.
Let us assume for a moment the proposition in the text; viz., that the
atoms are endowed with feeling. By the space coördinates _x_, _y_, _z_,
_x′_, _y′_, _z′_ ... of the atoms are determined _in the atoms_ internal
conditions α, β, γ, α′, β′, γ′ ... and _vice versa_. For we feel by
our senses our physical environment, and our physical invasions of our
environment are conditioned by our sensations. The idea is then at hand,
α, β, γ ... alone being directly given, to set up by the elimination of
_x_, _y_, _z_ ... equations directly between α, β, γ, α′, β′, γ′.... This
latter point of view would be very near to my present one, aside from the
fact that the latter wholly rejects metaphysical considerations.
[35] The following is a legitimate question: To what kind of nervous
processes is the sensation green to be mentally added. Such questions
can be solved only by special inquiry, and not by a reference in a
general way to motion and electric currents. How disadvantageous our
remaining satisfied with such general conceptions is, can be seen from
the fact that inquirers have been repeatedly on the brink of abandoning
the _specific energies_, one of the greatest acquisitions we have made,
simply because they were unable to discover any difference in the
currents of different sensory nerves. I was impelled as early as 1863
in my lectures on psycho-physics to call attention to the fact that the
_most diverse kinds_ of nervous processes can conceal themselves in a
current. Current is an abstraction and places in relief but one feature
of the process—the passage of energy though a transverse section. A
current in diluted sulphuric acid is something entirely different from a
current in copper. We must therefore also expect that a current in the
acoustic nerve is something entirely different from a current in the
optic nerve.
[36] It is the transitoriness of sense-perceptions that so easily leads
us to regard them as mere appearances as contrasted with permanent
bodies. I have repeatedly pointed out that unconditioned permanent states
do not exist in nature, that permanences of connection only exist. A
body is for me the same complex of sight-and-touch-sensations every time
that it is placed in the same circumstances of illumination, position in
space, temperature, and so forth. The supposed constancy of the body is
the constancy of the union of _A_, _B_, _C_ ... or the constancy of the
_equation f_(_A_, _B_, _C_ ...) = 0.