Michelson's Interferometer

[stratego]

Can anyone explain to me the concept behind A.A. Michelson's Interferometer? How does air pressure affect the fringing compared to if the experiment was carried out in a vacuum?

How many fringe cycles should you see if the final vacuum chamber pressure is a fraction of the normal air pressure. The answer would be in terms of variables: (wavelength, final pressure, and chamber thickness).

I was given two equations: n=index of reflection
n(air)=1+delta : for normal pressure
n(air)=1+delta/2 : for 1/2 the pressure

 

[slothman]

It's not air pressure but ether pressure. The ether is what people thought light waved in back then. Sound waves air while light waves ether. Now we know the ether doesn't exist but they didn't know that then. In that experiment they were thinking that the Earth moving through the ether would create different characteristics for light if light were moving parallel to the Earth moving versus light moving perpindicular. The speed difference would create interference.