Re: How did Michelson set up his famous experiment?

Greetings:

Many of us that grew up in Southern California with an early interest in 
science have made pilgrimages during our school days to the 254 cm (100 
inch) telescope on Mt. Wilson and the 508 cm (200 inch) telescope on Mt. 
Palomar. Part of these trips were mountain hikes to the various sites of A. 
A. Michelson’s speed of light experiments which now have historic markers 
some of which can be seen on the Mt. Wilson web site at:

 
Speed_of_Light



The web site answers one of your questions:
" In preparation for this experiment, the U.S. Coast & Geodetic Survey 
measured the distance between Mount Wilson and Mount San
Antonio (also known as Old Baldy), nearly 22 miles, with extreme accuracy. 
Baseline Road in eastern Los Angeles County is a
reminder of that accomplishment." 

This was a remarkable surveying accomplishment in the 1920s as was the 
determination of the height of Mt. Everest by surveying techniques in the 
19th century. We have to give those old guys credit. (Now I am one of those 
old guys!). Michelson also had a mirror site on the slopes of Mt. San 
Jacinto near Palm Springs, California which is over 120 km (80 miles) from 
Mt. Wilson. These long distance experiments are generally unknown because 
they were not as accurate as the 35 km (22 miles) experiments and were 
discounted.

Aligning the mirrors would not have been a difficult task. In the 35 km 
experiments Michelson used concave primary mirrors in a Newtonian telescope 
configuration at each end of the experiment. On the Mt. San Antonio mirror 
he placed a flat secondary mirror at the primary focus to retro-direct the 
incoming modulated light back toward Mt. Wilson. It is common practice to 
insert a standard Newtonian secondary mirror and eyepiece in place of the 
flat mirror and turn it into a Newtonian telescope. In the clear mountain 
air all you would then need is a 100 watt lamp bulb at the Mt. Wilson site 
to align the Mt. San Antonio mirror. This is still a common practice today 
for aligning laser communication links. A built in flip mirror is placed in 
the primary optics to convert the communication optics into telescopes for 
visual link alignment. 

I do not know what size primary mirrors Michelson used. The experiment is 
described in detail in the Astrophysical Journal, 1927, Vol 65, page 1. We 
do not have that old journal in our library; however, I was astounded to 
find a photocopy of Michelson’s hand written laboratory note book in our 
library. The notebook covers his first speed of light experiments, data 
and all,  which were conducted at the U. S. Naval Academy in 1878!

If you are interested e-mail me a FAX number and I’ll send you a copy of a 
few of Michelson's notebook pages.

There also is an interesting Michelson web site with links at: 

http://hum.amu.edu.pl/~zbzw/ph/sci/aam.htm


Best Regards, Your Mad Scientist
Adrian Popa