Max Abraham

“ However, for our system of electrodynamics of moving bodies, the vectors and are of lower importance than the vectors . When we, under elimination of and , directly connect those four vectors with each other, then the relatedness of the theories of Minkowski and Lorentz will become clear. ”

“ The first two terms are contributions of the aether in the sense of Lorentz's theory, the two latter ones are to be seen as contributions of polarized matter to the electromagnetic momentum density. We begin to calculate the energy current. ”

“ This partially stems from the fact, that E. Cohn's approach for the relative stresses is not entirely identical with (Va) ; he namely sets at this place instead of , probably with the intention to remove the torque of the relative stresses. The difference in the value of the force contribution stemming from the relative stresses, which is caused by that, can immediately be found
Only then we have seen the vanishing of as necessary, when – as in the theory of Hertz – no electromagnetic momentum comes into play. ”

“ Theory of E. Cohn.
E. Cohn based the electrodynamics of moving bodies on the following connecting equations
From them it follows, that when and are set equal to zero:
Now, since relation (18) requires
one thus places Cohn's theory in our system, by setting
In Cohn's electrodynamics, the momentum density has to be set equal to the relative ray divided by .
That relation (18a) is satisfied by (26) and (27) , can easily be confirmed by considering, that the identity
exists. ”

“ If gives the momentum exerted by the electromagnetic field, then the energy converted into non-electromagnetic forms, is given by the sum of Joule-heat and work of the ponderomotive force. For the Joule-heat, according to main equation (III) and (59d) , it is given
while the performance of work of force , is given from (60)
If one now considers, that the calculation of the ponderomotive force is based on the presuppositions ”

“ The comparison with (20) gives the important relation
If one inserts Minkowski's connecting equations between the electromagnetic vectors into our system, then the momentum density in the moving body becomes equal to the energy current divided by . ”

“ One can – because according to the things said, the component of coinciding with the direction of vector , is equal to zero – also write
By that, condition (18a) is shown to be valid, and at the same time the gap in the previous derivation of the value of is closed. ”