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Although the estimated difference between these two times is

exceedingly small, Michelson and Morley performed an experiment

involving interference in which this difference should have been

clearly detectable. But the experiment gave a negative result-a

fact very perplexing to physicists. Lorentz and FitzGerald

rescued the theory from this difficulty by assuming that the

motion of the body relative to the aether produces a contraction

of the body in the direction of motion, the amount of contraction

being just sufficient to compensate for the difference in time

mentioned above. Comparison with the discussion in Section XII

shows that also from the standpoint of the theory of relativity

this solution of the difficulty was the right one. But on the

basis of the theory of relativity the method of interpretation is

incomparably more satisfactory.