2 5 0 D O C . 3 1 8 C R I S I S O F T H E O R E T I C A L P H Y S I C S century, physicists were convinced that these fundamental laws of mechanics would have to be the basis of absolutely all theoretical physics, i.e., that every phys- ical theory would ultimately have to be based on mechanics. So the basis of physics seemed to have been finally erected and a theoretical physicist’s work seemed to be to conform the theory through specialization and dif- ferentiation to the ever-growing abundance of investigated phenomena. No one thought about the possibility that the foundations of physics would have to be changed. Then, as a consequence of Faraday’s and Maxwell’s researches, it gradu- ally became obvious that the foundations of mechanics failed for electromagnetic phenomena. This change took place in a number of stages. Initially both the above- named pioneers realized that electromagnetic processes cannot be represented with the theory of unmediated forces by action-at-a-distance. According to Newton, all forces that can produce accelerations of material points are attributable to an instantaneous influence that the rest of the material points individually exert on the observed material point. As an alternative to this theory of unmediated action-at-a-distance, Maxwell and Faraday posited the theory of electromagnetic fields. According to this theory, all dissemination of electric force is based not on instantaneous action-at-a-distance but on a propagation-con- ducive state of space or the ether: the electromagnetic field.[3] The energy-endowed field, describable by continuous space functions, assumed physical reality along- side the movable mass point that according to Newton’s theory had figured as the sole carrier of energy. It is known that Hertz helped bring about general recognition of this conception through his experiments on the propagation of electric force.[4] At first, the extent of the revolutionary character of field theory was not fully realized.[5] Maxwell himself was still convinced that electrodynamic processes were conceivable as processes of motion by the ether he even used mechanics to forge ahead to the field equations. In the interim, however, it became more and more clear that it was impossible to derive the electromagnetic equations from mechanical ones. In search of a unified basis for physics one was eventually com- pelled to try the opposite and derive the mechanical equations from electromag- netic ones.[6] This attempt suggested itself even more after J. J. Thomson realized that an electromagnetic inertia existed for electrically charged bodies and after M. Abraham showed that the inertia of electrons was interpretable purely electromagnetically.[7] With the attribution of inertia to electromagnetic processes, a complete revolution in the foundations of physics had come to pass, at least in principle. Instead of the mass point as the ultimate of reality, the electromagnetic field entered as a fundamental elementary building block of theoretical physics. A theoretical construction of matter on a purely electromagnetic basis is generally [p. 2] [p. 3]