[填空题]
One of the beams of an interferometer (Fig. 24–59) passes0q 62*ftg:yx c5vfgm x.wpwa6 through a small tw*n:rzk+adg+r : vq0jjs /i;glass container containing a cavity 1.30 cm deep. When a gas is allowed to slowly fill the container, a total of 236 dark fringes are counted to move past a reference line. The light used has a wavelength of 610 nm. Calculate the index of refraction of the gas, assuming that the interferometer itwk+0+a:i/ rgs *;:rzdjqnj vs in vacuum. $n_{gas}$
