Now by (OA′/B*D*) is to be understood the ratio of the two vectors in question. It is clear that this proposition at once shows the covariant character with respect to a Lorentz-group. Let us now ask how the space-time filament of F behaves when the material point F* has a uniform translatory motion, _i.e._, the principal line of the filament of F* is a line. Let us take the space time null-point in this, and by means of a Lorentz-transformation, we can take this axis as the t-axis. Let _x_, _y_, _z_, _t_, denote the point B, let τ* denote the proper time of B*, reckoned from O. Our proposition leads to the equations (25) _d²__x_/_d_τ² = - _m_*_x_/(_t_ - τ*)², _d²__y_/_d_τ² = - _m_*_y_/(_t_ - τ*)³ _d²__z_/_d_τ² = -_m_*_z_/(_t_ - τ*)³, (26) _d²__t_/_d_τ² = -_m_*/(_t_ - τ*)² _d_(_t_ - τ*)/_dt_ where (27) _x²_ + _y²_ + _z²_ = (_t_ - τ*)² and (28) (_dx_/_d_τ)² + (_dy_/_d_τ)² + (_dz_/_d_τ)² = (_dt_/_d_τ)² - 1. In consideration of (27), the three equations (25) are of the same form as the equations for the motion of a material point subjected to attraction from a fixed centre according to the Newtonian Law, only that instead of the time _t_, the proper time τ of the material point occurs. The fourth equation (26) gives then the connection between proper time and the time for the material point. Now for different values of τ′, the orbit of the space-point (_x_ _y_ _z_) is an ellipse with the semi-major axis _a_ and the eccentricity _e_. Let E denote the eccentric anomaly, Τ the increment of the proper time for a complete description of the orbit, finally _n_Τ = 2π, so that from a properly chosen initial point τ, we have the Kepler-equation (29) _n_τ = E - _e_ sin E. If we now change the unit of time, and denote the velocity of light by _c_, then from (28), we obtain (30) (_dt_/_d_τ)² - 1 = (_m_*/_ac²_) (1 + _e_ cos E)/(1 - _e_ cos E) Now neglecting _c⁻⁴_ with regard to 1, it follows that _ndt_ = _nd_τ [ 1 + ½ _m_*/_ac²_ (1 + _e_ cos E)/(1 - _e_ cos E) ] from which, by applying (29), (31) _nt_ + const = (1 + ½ _m_*/_ac²_) _n_τ + _m_*/_ac²_ Sin E. the factor _m_*/_ac²_ is here the square of the ratio of a certain average velocity of F in its orbit to the velocity of light. If now _m_* denote the mass of the sun, _a_ the semi major axis of the earth’s orbit, then this factor amounts to 10⁻⁸. The law of mass attraction which has been just described and which is formulated in accordance with the relativity postulate would signify that gravitation is propagated with the velocity of light. In view of the fact that the periodic terms in (31) are very small, it is not possible to decide out of astronomical observations between such a law (with the modified mechanics proposed above) and the Newtonian law of attraction with Newtonian mechanics. Footnote 29: