In Michaelson Morley experiment, the aim was to find the time difference from which the relative velocity between ether and the earth could be estimated. However, no shift was observed. Hence it proved, that ether has no observable properties and that velocity of light is same in all directions.

Interferometers are for measuring the interference properties of light waves. It gives very accurate and precise measurements. It is due to this purpose, that it was used in Michaelson Morley experiment, so as to be able to measure the fringe shift that occurs when light is propagated in different directions.

Michaelson designed a special device that would have accuracy far exceeding any other device. It was called Michaelson Interferometer. Using a light of wavelength 600 nm, a fringe shift of 0.04 was expected.

By using Michaelson Interferometer, fringes of equal inclination are obtained. These fringes are called as Haidinger’s fringes. All the fringes are concentric circles.

Here, d = 0.0589 X 10^-3m, n = 200
Therefore, λ=2dn
= 2 X 0.0589 X 10^-3/200
= 5890 Å