First there was the observation by Michelson who back in the late 1880s had done very precise interferal metric measurements of the hydrogen lines and had observed that the 656 nanometer line 3 associated with the transition of n equals 3 to n equals 2 was, in fact, a doublet.

首先是麦克逊,在1880年底的观察,他以公制单位对氢原子的光谱线,作了准确的，无其他因素干扰的，测量,发现当n值由3变为2时,会同时得到波长为656纳米的谱线3,实际上是有两条线。

麻省理工公开课 - 固态化学导论课程节选