Hi Hilmar,

I found this on the Gravity Probe B web site under [Project Timeline].

http://einstein.stanford.edu/content/timeline/timeline.html

The fact that the speed of light is constant regardless of the speed of the observer changed everything.


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1887
Michelson and Morley Experiment showing the speed of light remains constant - Einstein's theories sprang from a ground of ideas prepared by decades of experiments. One of the most striking, in retrospect, was done in Cleveland, Ohio, by Albert Michelson and Edward Morley in 1887. Their apparatus was a massive stone block with mirrors and crisscrossing light beams, giving an accurate measurement of any change in the velocity of light. Michelson and Morley expected to see their light beams shifted by the swift motion of the earth in space. To their surprise, they could not detect any change. It is debatable whether Einstein paid heed to this particular experiment, but his work provided an explanation of the unexpected result through a new analysis of space and time.

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Regards,

LelandJ