1. The problem statement, all variables and given/known data One of the beams of an interferometer, as seen in the figure below, passes through a small glass container containing a cavity D = 1.34 cm deep. When a gas is allowed to slowly fill the container, a total of 222 dark fringes are counted to move past a reference line. The light used has a wavelength of 598 nm. Calculate the index of refraction of the gas, assuming that the interferometer is in vacuum *Similar to Michelson-Morley Experiment* 2. Relevant equations Based off of assumption: Snells Law: n1*sin(theta1)=N2*SIN(THETA2) T=1/f=[lamb]/c t1=(2*L1/c)*(1/sqrt(1-(v^2/c^2))) 3. The attempt at a solution One variable I tried to solve for was t1 by finding the frequency, but that was unsuccessful and to be honest I'm not even sure on how to attempt this problem. If anyone has a hint as to where I could start, I would really appreciate it!