(97) (1/i)K₄ = ∂Ty/∂x - ∂Ty/∂y - ∂Tz/∂z - ∂Tt/∂t = sxEx + syEy + szEz
- ½ Φ[=Φ]∂ε/∂t - ½ ψ[=ψ]∂μ/∂t + (εμ - 1)/√(1 - u²) (W∂u/∂t).
It is my opinion that when we calculate the ponderomotive force which acts upon a unit volume at the space-time point x, y, z, t, it has got, x, y, z components as the first three components of the space-time vector
K + (ωK)ω,
This vector is perpendicular to ω; the law of Energy finds its expression in the fourth relation.
The establishment of this opinion is reserved for a separate tract.
In the limiting case ε = 1, μ = 1, σ = 0, the vector N = 0, S = ρω, ωK = 0, and we obtain the ordinary equations in the theory of electrons.
APPENDIX
Mechanics and the Relativity-Postulate.
It would be very unsatisfactory, if the new way of looking at the time-concept, which permits a Lorentz transformation, were to be confined to a single part of Physics.
Now many authors say that classical mechanics stand in opposition to the relativity postulate, which is taken to be the basis of the new Electro-dynamics.