vibrations and sound-perception, of ether-vibrations and light-perception. A certain, even quantitatively definite relation obtains between the intensity of stimulation and the stimulated effect, but that relation is neither one of equivalence nor of convertibility. This fact is universal in Nature, but becomes the more obvious the less the mutually affecting substances resemble each other. It is just as impossible that one kind of force can be converted into another kind of force, as it is impossible for any kind of force to originate out of nothing, or to exist without substratum.
A "force-directing" machine or apparatus corresponds to a well-known intelligible fact. A "force-transforming" machine or apparatus corresponds to something altogether unintelligible. If substances had really any such transforming effect on forces, even then they would themselves constitute specifically intervening powers. But this also is hyperbolical, for it does not adequately express the part which substances actually play in the manifestation of forces.
The now so famous notion of the equivalence and convertibility of forces indicates certainly a desirable attempt to bring under the grasp of Science the subtile balance of energies constituting our phenomenal world, but it partakes still too much of the old metaphysical weakness, under which we are wont to seize the shadow and lose the substance. By admitting molecular affections into the vicious circle of mechanical equivalence, it has, however, imported into it an insuppressibly qualitative element, that sooner or later, by its intense expansiveness, will break the narrowing spell, and open to scientific knowledge new fields of unexpected wealth.
The whole mechanical view of Nature rests chiefly on the supposition that effects are equal to their causes, that they are indeed the causes themselves, metamorphosed in appearance. This notion is radically erroneous, and can never lead to an understanding of reality. Causa non æquat effectum. In Nature there exists nothing corresponding to the so-called efficient causes of science, whether single or plural. The scientific conception of cause is a dynamical fiction, made to suit a realm of phantasmal inertia, in which molecularly imperturbable masses pursue forever an unopposed course in a resistless medium. How can we gain an insight into reality by always mathematizing it away?
In Nature all manifestations are the work of opposition and perturbation; agitation of preexisting states, and subversion of the same. It is in this intrinsic potentiality and mutualof so-called masses that Nature has its being, its subsistence, and its perfectibility. The substrata of reality are not merely ponderable or imponderable vehicles of locomotion; but concentrations of actual and potential energies, thrilling through and through with consonant sensitiveness, reverberating with an accent of their own every commotion from the centre of the skies to the centre of the earth.