In 1921, the experimental physicist Rudolf Ladenburg put forward the first quantum interpretation of optical dispersion. Theoretical physicists had tried to explain dispersion from the point of view of quantum theory ever since 1913, when Niels Bohr proposed his quantum model of atom. Yet, their theories proved unsuccessful. It was Ladenburg who gave a breakthrough step toward our quantum understanding of dispersion. In order to understand Ladenburg’s step, I analyze Ladenburg’s experimental work on dispersion prior to 1913, the reasons why the first theories of dispersion after 1913 were not satisfactory, and Ladenburg’s 1921 proposal. I argue that Ladenburg’s early experimental work on dispersion is indispensable to understand his 1921 paper. The specific kind of experiments he performed before 1913, the related interpretative problems, and the way he tried to solve them, led him reapproach the dispersion problem in 1921 in a way that was completely different from the way theoretical physicists had done it before.

1921年，实验物理学家鲁道夫·拉登堡（Rudolf Ladenburg）首次提出了光学色散的量子解释。自1913年尼尔·玻尔（Niels Bohr）提出原子量子模型以来，理论物理学家就一直试图从量子理论的角度来解释色散。然而，他们的理论被证明是失败的。拉登堡朝着我们对色散的量子理解迈出了突破性的一步。为了理解拉登堡的步骤，我分析了拉登堡在1913年之前的色散实验工作，1913年之后的第一个色散理论为何不令人满意以及拉登堡在1921年提出的建议。我认为拉登堡（Ladenburg）早期的色散实验工作对于理解他的1921年论文是必不可少的。他在1913年之前进行的特定类型的实验，相关的解释性问题，