Circular fringes in Michelson interferometer

The rays reflected by mirrors M1 and M2 meet at the glass G. For each ray(specifically 1 and 2 in the figure which may go on 1,2,3... for an extended object as is required for the experiment) as the splitted beams meet at G the path difference for each ray(1,2,3..) would be the same (x2-x1) according to the figure, then why do we see circular fringes at the screen?

• Not sure what you mean, the path difference of one of the two arms can be adjusted so they aren't the same between leg 1 and leg 2 (like in the case of gravitational wave detection). There is interference only when the path length difference isn't an integer number of wavelengths. Commented Jan 7, 2021 at 20:02
• Maybe I am not able to frame my question properly. I am trying to say that if for instance we take beam 2(in the figure) then the split beam that reaches mirror M2(vertical) and returns back to G and the one that reaches M1 and returns to G, the path difference between the two beams(split parts of Beam 2) is same (x2-x1) and same is true for all the other beams(1,2,....), then how do we see circular fringes? Commented Jan 7, 2021 at 20:44
• Commented Apr 24 at 18:27