#211.
The particular bodies in which gravity is realized have, as the determinations of their different natures, the moments of their concept. One body, therefore, is the general center of being in itself. Opposing this extreme stands individuality, existing outside of itself and without a center. But the particular bodies are others, which stand in the determination of being outside of themselves and are at the same time, as being in themselves, also centers for themselves, and are related to the first body as to their essential unity.
#212.
(1) The motion of bodies of relative centrality, in relation to bodies of abstract, general centrality, is absolutely free motion, and the conclusion of this system is that the general central body is brought together through relative centrality with dependent corporeality.
As is well-known, the laws of absolutely free motion were discovered by Kepler, a discovery of immortal fame. Kepler proved them, too, in the sense that he found the general expression for the empirical data (cf. #145). Since then it has become a commonplace that Newton first found the proofs of these laws. Not often has fame been more unjustly transferred from the first discoverer to another. Here I only want to point out what has basically already been admited [sic] by mathematicians, namely: (1) that the Newtonian formulas can be derived from Keplerian laws; (2) that the Newtonian proof of the proposition that a body governed by the law of gravitation moves in an ellipse around the central body proceeds in general in a conic section, whereas the main point that was to be proven consists precisely in this, that the course of such a body is neither a circle nor any other conic section, but solely the ellipse. The conditions which make the course of the body into a specific conic section are referred back to an empirical condition, namely, a particular situation of the body at a specific point in time, and to the contingent strength of an impulse which it is supposed to have received at the beginning. (3) Newton's "law" of the force of gravity has likewise only been demonstrated inductively from experience.
On closer inspection it appears that what Kepler, in a simple and sublime manner, articulated in the form of laws of celestial motion, Newton converted into the nonconceptual, reflective form of the force of gravity. The whole manner of this "proof" presents in general a confused tissue of lines of merely geometrical construction to which a physical meaning of independent forces is given, of the empty concepts of the understanding of a force of acceleration, of particles of time, at whose beginning those forces always play a renewed role, and of a force of inertia, which presumably continues its previous effect, and so on. A rational proof of the quantitative determinations of free motion can only rest on the determinations of the concepts of space and time, the moments whose relation is motion.
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