H. A. Lorentz suggested 15 years before Einstein’s 1905 paper that the null effect of the Michelson-Morley experiment could be accounted for by a contraction of that arm of the interferometer lying parallel to Earth’s motion through the ether to a length L = L_p(1-v²/c²)^-1/2. He thought of this, incorrectly, as an actual shrinking of matter. By about how many atomic diameters would the material in the parallel arm of the interferometer have had to shrink in order to account for the absence of the expected shift of 0.4 of a fringe width? (Assume the diameter of atoms to be about 10^-10 m.)