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Einstein’s Investigations of Galilean Covariant
Electrodynamics prior to 1905
John D. Norton1
Department of History and Philosophy of Science
University of Pittsburgh
jdnorton@pitt.edu
Einstein learned from the magnet and conductor thought experiments how to use field
transformation laws to extend the covariance to Maxwell’s electrodynamics. If he
persisted in his use of this device, he would have found that the theory cleaves into two
Galilean covariant parts, each with different field transformation laws. The tension
between the two parts reflects a failure not mentioned by Einstein: that the relativity of
motion manifested by observables in the magnet and conductor thought experiment does
not extend to all observables in electrodynamics. An examination of Ritz’s work shows
that Einstein’s early view could not have coincided with Ritz’s on an emission theory of
light, but only with that of a conveniently reconstructed Ritz. One Ritz-like emission
theory, attributed by Pauli to Ritz, proves to be a natural extension of the Galilean
covariant part of Maxwell’s theory that happens also to accommodate the magnet and
conductor thought experiment. Einstein's famous chasing a light beam thought
experiment fails as an objection to an ether-based, electrodynamical theory of light.
However it would allow Einstein to formulate his general objections to all emission
theories of light in a very sharp form. Einstein found two well known experimental
results of 18th and19th century optics compelling (Fizeau’s experiment, stellar
aberration), while the accomplished Michelson-Morley experiment played no memorable
role. I suggest they owe their importance to their providing a direct experimental
grounding for Lorentz’ local time, the precursor of Einstein’s relativity of simultaneity,
and do it essentially independently of electrodynamical theory. I attribute Einstein’s
success to his determination to implement a principle of relativity in electrodynamics,
but I urge that we not invest this stubbornness with any mystical presc