By neglecting all differentiations with regard to time, this leads, when μ = ν =4, to the expression
The last of the equations (53) thus leads to
(68) ▽² g₄₄ = κρ.
The equations (67) and (68) together, are equivalent to Newton’s law of gravitation.
For the gravitation-potential we get from (67) and (68) the exp.
(68a.) -κ/(8π) ∫ ρdτ/r
whereas the Newtonian theory for the chosen unit of time gives
-K/c² ∫ρdτ/r,
where K denotes usually the gravitation-constant. 6.7 x 10⁻⁸; equating them we get