Poincaré identified that there are only two manners to explain forces of any origin:
Either, all of Nature is of electromagnetic origin.
Or …something which would be due to our methods of measurement
and wisely said
Perhaps it would be enough to give up this definition, so that the theory of Lorentz is as completely rejected as it was the system of Ptolemy by the intervention of Copernicus. If that happens one day, it will not prove that the effort made by Lorentz was useless; because Ptolemy, no matter what we think about him, was not useless for Copernicus.
These site explores Poincaré vision that Nature is of electromagnetic origin.