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344 CONTRIBUTIONS TO SCIENCE
it is primarily the simplicity of its premises and its intimate
connection with what is already known (viz., the laws of the
pure gravitational field) that speak in favor of the theory to
be discussed here. It may, however, be of interest to a wide
group of readers to become acquainted with the train of thought
which can lead to endeavors of such an extremely speculative
nature. Moreover, it will be shown what kinds of difficulties
are encountered and in what sense they have been overcome.
In Newtonian physics the elementary theoretical concept
on which the theoretical description of material bodies is based
is the material point, or particle. Thus matter is considered
a priori to be discontinuous. This makes it necessary to consider
the action of material points on one another as "action
at a distance." Since the latter concept seems quite contrary to
everyday experience, it is only natural that the contemporaries
of Newton-and indeed Newton himself-found it difficult to
accept. Owing to the almost miraculous success of the N ewtonian
system, however, the succeeding generations of physicists
became used to the idea of action at a distance. Any doubt
was buried for a long time to come.
But when, in the second half of the nineteenth century, the
laws of electrodynamics became known, it turned out that these
laws could not be satisfactorily incorporated into the Newtonian
system. It is fascinating to muse: Would Faraday have discovered
the law of electromagnetic induction if he had received
a regular college education? Unencumbered by the traditional
way of thinking, he felt that the introduction of the "field"
as an independent element of reality helped him to coordinate
the experimental facts. It was Ma.xwell who fully comprehended
the significance of the field concept; he made the
fundamental discovery that the laws of electrodynamics found
their natural expression in the differential equations for the
electric and magnetic fields. These equations implied the
existence of waves, whose properties corresponded to those
of light as far as they were known at that time.
This incorporation of optics into the theory of electromagnetism
represents one of the greatest triumphs in the
striving toward unification of the foundations of physics; Max-