However, since only matter and electromagnetic energy are directly observable by experiment (not the non-em-fluid), Poincaré's resolution still violates the reaction principle and the COM-theorem, when an emission/absorption process is practically considered.
However, Poincaré's idea of momentum and mass associated with radiation proved to be fruitful, when Max Abraham introduced[REF] the term "electromagnetic momentum", having a field density of E_{em}/c^2 per cm3 and E_{em}/c per cm2.