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Now before the advent of the theory of relativity it had always

tacitly been assumed in physics that the statement of time had an

absolute significance, i.e. that it is independent of the state

of motion of the body of reference. But we have just seen that

this assumption is incompatible with the most natural definition

of simultaneity; if we discard this assumption, then the conflict

between the law of the propagation of light in vacuo and the

principle of relativity (developed in Section VII) disappears.