112 RELATIVITY, THE SPECIAL THEORYMaxwell requested and received data on the Jovian system from David Peck
Todd, Director of the Nautical Almanac Office in Washington, D.C. On March
19, 1879, Maxwell sent a letter of thanks in which he referred Todd to his ency-
clopedia article and in particular reiterated his remark on the second-order nature
of terrestrial experiments. This letter (not reproduced in his collected papers) was
written when Maxwell had less than eight months to live and Einstein was five
days old. After Maxwell's death, the letter was forwarded to the secretary of the
Royal Society, who saw to its publication in the January 29,1880, issue of Nature
[M2].
A year and a half later, in August 1881, there appeared an article in an issue
of the American Journal of Science, authored by Albert A. (for Abraham)
Michelson, Master, U.S. Navy [M3]. Michelson, then on leave from the Navy
and doing post-graduate work in Helmholtz's laboratory in Berlin, had read
Maxwell's 1879 letter. Being already an acknowledged expert on measurements
of the velocity of light (he had by then published three papers on the subject [L2]),
he had concluded that Maxwell had underrated the accuracy with which terres-
trial experiments could be performed. The instrument he designed in Berlin in
order to measure Maxwell's second-order effect is known as the Michelson inter-
ferometer. In order not to be bothered by urban vibrations, Michelson performed
his experiments at the astrophysical observatory in nearby Potsdam. The method
he used was to compare the times it takes for light to travel the same distance
either parallel or transversely to the earth's motion relative to the aether. In his
arrangement a stationary aether would yield a time difference corresponding to
about an extra 1 /25 of a wavelength of yellow light traveling in the parallel direc-
tion, an effect that can be detected by letting the transverse and parallel beams
interfere. For easily accessible details of the experiment I refer the reader to text-
books* and state only Michelson's conclusion: there was no evidence for an aether
wind. 'The result of the hypothesis of a stationary aether is thus shown to be
incorrect, and the necessary conclusion follows that the hypothesis is erroneous,'
[M3].
Early in 1887 Michelson wrote to Rayleigh** that he was 'discouraged at the
slight attention the work received' [M4], a statement which perhaps was justified
if one counts the number of those who took note, but not if one considers their
eminence. Kelvin and Rayleigh, both of whom Michelson had met at Johns Hop-
kins University in 1884 [S3] certainly paid attention. So did Lorentz, who found
an error in Michelson's theory of the experiment [L3] and who was dubious about
the interpretation of the results [ L4]. Lorentz's misgivings and Rayleigh's urgings
contributed to Michelson's decision—he was now at the Case School of Applied
Science in Cleveland—to repeat his experiment, this time in collaboration with
Edward Williams Morley, a chemist from next-door Western Reserve University.
'See, e.g., [PI].
**For details of the Michelson-Rayleigh correspondence, see especially [S2] and [HI].