On the role of the Michelson-Morley experiment: Einstein in Chicago

This article discusses new material, published in Volume 12 of the Collected Papers of Albert Einstein, that addresses Einstein's knowledge of the Michelson-Morley experiment prior to 1905: in a lecture in Chicago in 1921, Einstein referred to the experiment, mentioned when he came upon it, and hinted at its influence. Arguments are presented to explain the contrast with Einstein's later pronouncements on the role of the experiment.