If we compare with this expression the previous formulæ[35] giving the elementary law about the ponderomotive action of moving electric charges upon each other, then we cannot but admit, that the relations which occur here reveal the inner essence of full simplicity first in four dimensions; but in three dimensions, they have very complicated projections. In the mechanics reformed according to the world-postulate, the disharmonies which have disturbed the relations between Newtonian mechanics and modern electrodynamics automatically disappear. I shall now consider the position of the Newtonian law of attraction to this postulate. I will assume that two point-masses _m_ and _m₁_ describe their world-lines; a moving force-vector is exercised by _m_ upon _m₁_, and the expression is just the same as in the case of the electron, only we have to write +_mm₁_ instead -_ee₁_. We shall consider only the special case in which the acceleration-vector of _m_ is always zero: then _t_ may be introduced in such a manner that _m_ may be regarded as fixed, the motion of _m_ is now subjected to the moving-force vector of _m_ alone. If we now modify this given vector by writing -([^.]1/√(1-(_v_²/_c²_)) instead of [._t_] ([._t_] = 1 up to magnitudes of the order (1[^.]/_c²_)), then it appears that Kepler’s laws hold good for the position (_x₁_, _y₁_, _z₁_), of _m₁_ at any time, only in place of the time _t₁_, we have to write the proper time τ₁ of _m₁_. On the basis of this simple remark, it can be seen that the proposed law of attraction in combination with new mechanics is not less suited for the explanation of astronomical phenomena than the Newtonian law of attraction in combination with Newtonian mechanics. Also the fundamental equations for electro-magnetic processes in moving bodies are in accordance with the world-postulate. I shall also show on a later occasion that the deduction of these equations, as taught by Lorentz, are by no means to be given up. The fact that the world-postulate holds without exception is, I believe, the true essence of an electromagnetic picture of the world; the idea first occurred to Lorentz, its essence was first picked out by Einstein, and is now gradually fully manifest. In course of time, the mathematical consequences will be gradually deduced, and enough suggestions will be forthcoming for the experimental verification of the postulate; in this way even those, who find it uncongenial, or even painful to give up the old, time-honoured concepts, will be reconciled to the new ideas of time and space,—in the prospect that they will lead to pre-established harmony between pure mathematics and physics. Footnote 30: Planck, Zur Dynamik bewegter systeme, Ann. d. physik, Bd. 26, 1908, p. 1. Footnote 31: H. Minkowski; the passage refers to paper (2) of the present edition. Footnote 32: Minkowski—Mechanics, appendix, page 65 of paper (2). Planck—Verh. d. D. P. G. Vol. 4, 1906, p. 136. Footnote 33: