It's a bit tricky to find a good description of the method, however it is possible to find the original paper published in the Astrophysical Journal in January 1927. Go to http://adsabs.harvard.edu/full/1927ApJ....65....1M . A diagram of the method is illustrated on page four.
The round trip distance between Mt. Wilson and Lookout Mountain (nee Mt. San Antonio) is
d = 2*22 miles = 70,840 meters. Dividing
d by by speed of light
c = 3x10
10 meters per second gives
ttof = 2.36x10
-4 seconds. Now if you have an octagonal mirror rotating at 528 revolutions per second the time between successive surfaces is
trot = (1/528)/8 = 2.36e-004, the same number.
So the return image should be in the same place. Michelson devised a clever way to measure a displacement from this perfect agreement by controlling the mirror rotation rate. When the rate was 528 the return image was perfectly aligned with the outgoing image, otherwise it was shifted a bit.
LeeH
(published on 10/05/2012)
