In 1885, Michelson began a collaboration with Edward Morley, spending considerable time and money to confirm with higher accuracy Fizeau’s 1851 experiment on Fresnel’s drag coefficient, ^{[ 5 ]} to improve on Michelson’s 1881 experiment, ^{[ 1 ]} and to establish the wavelength of light as a standard of length. ^{[ 6 ] [ 7 ]} John Brashear made the high-quality optics for the Interferometer in his Allegheny-Observatory-affiliated shop. At this time Michelson was professor of physics at the Case School of Applied Science, and Morley was professor of chemistry at Western Reserve University (WRU), which shared a campus with the Case School on the eastern edge of Cleveland. Michelson suffered a mental health crisis in September 1885, from which he recovered by October 1885. Morley ascribed this breakdown to the intense work of Michelson during the preparation of the experiments. In 1886, Michelson and Morley successfully confirmed Fresnel’s drag coefficient—this result was also considered as a confirmation of the stationary aether concept. ^{[ A 2 ]}

This result strengthened their hope of finding the aether wind. Michelson and Morley created an improved version of the Michelson experiment with more than enough accuracy to detect this hypothetical effect. The experiment was performed in several periods of concentrated observations between April and July 1887, in the basement of Adelbert Dormitory of WRU (later renamed Pierce Hall, demolished in 1962). ^{[ A 11 ] [ A 12 ]}

As shown in the diagram to the right, the light was repeatedly reflected back and forth along the arms of the interferometer, increasing the path length to 11 m (36 ft). At this length, the drift would be about 0.4 fringes. To make that easily detectable, the apparatus was assembled in a closed room in the basement of the heavy stone dormitory, eliminating most thermal and vibrational effects. Vibrations were further reduced by building the apparatus on top of a large block of sandstone (Fig. 1), about a foot thick and five feet (1.5 m) square, which was then floated in a circular trough of mercury. They estimated that effects of about 0.01 fringe would be detectable.