Let it be supposed that the gravitation of the two bodies towards each otherat the given distance has varied, and the conclusions drawn are no longertrue. Nor is it only in their concrete data that the reasonings of terrestrialand celestial physics assume the Persistence of Force. The equality of actionand reaction is taken for granted from beginning to end of either argument;and to assert that action and reaction are equal and opposite, is to assertthat Force persists. The implication is that there cannot be an isolatedforce, but that any force manifested implies an equal antecedent force fromwhich it is derived, and against which it is a reaction.
We might indeed be certain, even in the absence of any such analysis asthe foregoing, that there must exist some principle which, as being the basisof science, cannot be established by science. All reasoned-out conclusionswhatever must rest on some postulate. As before shown (§23), we cannotgo on merging derivative truths in those wider truths from which they arederived, without reaching at last a widest truth which can be merged in noother, or derived from no other. And the relation in which it stands to thetruths of science in general, shows that this truth transcending demonstrationis the Persistence of Force. To this an ultimate analysis brings us down,and on this a rational synthesis must build up. §62. But now what is the force of which we predicate persistence?
That which the word ordinarily stands for is the consciousness of musculartension -- the feeling of effort which we have either when putting somethingin motion or when resisting a pressure. This feeling, however, is but a symbol.
In §18 it was said that though, since action and reaction are equaland opposite, we are obliged to think of the downward pull of a weight asequal to the upward pull which supports it, and though the thought of equalitysuggests kinship of nature, yet, as we cannot ascribe feeling to the weight,we are obliged to admit that Force as it exists beyond consciousness hasno likeness to force as we conceive it, though there is between them thekind of equivalence implied by simultaneous variation. The effort of onewho throws a cricket ball is followed by the motion of the ball through space,and its momentum is re-transformed into muscular strain in one who catchesit. What the force was when it existed in the flying cricket ball it is impossibleto imagine: we have no terms of thought in which to represent it. And itis thus with all the transformations of energy taking place in the worldaround. Those illustrations given in §66, showing the changes of formwhich energy undergoes and the equivalence between so much of it in one formand so much in another, fail to enlighten us respecting the energy itself.
It assumes under this or that set of conditions this or that shape, and thequantity of it is not altered during its transformations. For that interpretationof things which is alone possible for us this is all we require to know --that the force or energy manifested, now in one way now in another, persistsor remains unchanged in amount. But when we ask what this energy is, thereis no answer save that it is the noumenal cause implied by the phenomenaleffect.
Hence the force of which we assert persistence is that Absolute Forcewe are obliged to postulate as the necessary correlate of the force we areconscious of. By the Persistence of Force, we really mean the persistenceof some Cause which transcends our knowledge and conception. In assertingit we assert an Unconditioned Reality, without beginning or end.
Thus, quite unexpectedly, we come down once more to that ultimate truthin which, as we saw, Religion and Science coalesce -- the continued existenceof an Unknowable as the necessary correlative of the Knowable.
