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results of investigation in various provinces of molecular 
physics, no longer tenable,” &c. This view, I take it, is 
tacitly assumed in all expositions of molecular physics, as, for 
example, in Professor Clerk-Maxwell’s paper on the Theory 
of Molecules, read before the British Association at Bradford, 
in 1873. Matter, we are then apparently obliged to admit, 
is really existing (if there exists an external world — which we 
may assume to be the case), but of its real, substantive nature 
we have no knowledge. For Plato, it was irrational and, in 
itself, unreal ; for Aristotle merely potential ; for Descartes 
it was extension; for Kant (at the age of twenty years) 
“ working force,” or (at a later period) simply a “ necessary 
formula of thought ” ; while Hegel treated it as the “ produce 
of place and motion,” and the “ means for the self-realization 
of spirit” ; Helmholtz declares it an abstraction, and Huxley 
a “ form of consciousness.” Evidently none of these men 
knew or knows what matter intrinsically is ; and Du Bois- 
Keymond says that we never can know it ( Ueber die Grenzen 
des Naturerlcennens, Leipzig, 1872, p. 34). And this is true, 
because matter cannot be conceived by us in sufficiently posi- 
tive terms ; we can only think of it (except in so far as we 
attribute to it “forces,” our idea of which is formed after the 
analogy of ivhat ice know in our own conscious experience) as 
not possessing this, that, and the other attribute of the only 
kind of existence of which we have direct knowledge, namely, 
of ideal existence. As to force, in the second place, it too is 
merely an abstraction (Helmholtz, Ueberweg, and others), or 
a “ form of consciousness ” (Huxley), the formation of the 
idea being “ a sort of rhetorical artifice of the human brain 
which resorts to figure when its ideas are too vague for clear 
expression” (Du Bois-Reymond), unless it be in an important 
measure identical with that of which we believe ourselves con- 
scious in our voluntary actions. 
Matter and “ physical ” force are so little known, or rather 
are so absolutely unknown (apart from the analogy of ideal 
force), that, without claiming or seeking to arrive at the what 
(the substantive nature) of things, physical science seeks only 
to ascertain the laws and order of phenomena, which latter it 
regards with reason as phenomena (“ modes”) of motion. 
(“ Under the influence of this idea [the idea of the conser- 
vation of energy], we see in our time physics transformed and 
established as, in the strictest sense of the term, doctrine of 
motion”; see Dr. H. Boehmer, Geschichte der EntwicTcelung 
der naturwissenschaftlichen Weltanschauung in Deutschland, 
Gotha, 1872; cf. also Emil du Bois-Reymond, Ueber die 
Grenzen des Naturerlcennens , pp. 2 ct seq., Leipzig, 1872.) The 
