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immediately follows. If referred to the system K′, the

propagation of light takes place according to this equation. We

thus see that the velocity of transmission relative to the

reference-body K′ is also equal to c. The same result is obtained

for rays of light advancing in any other direction whatsoever. Of

cause this is not surprising, since the equations of the Lorentz

transformation were derived conformably to this point of view.

XII.

THE BEHAVIOUR OF MEASURING-RODS AND CLOCKS IN MOTION