Michelson had only two beams, but he had no way to stabilize them, so Michelson had to wait for that rare moment when the two beams arrived at precisely the same time and place by chance.

• 米切尔森只用了两束光线，但是他无法使之稳定，所以米切尔森不得不等待这两束光线偶然分毫不差地同时到达同一地点的稀有时刻。