[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.