Summary

The central thesis of Hertz's 1926 Nobel lecture is that his experiments with electron collisions in mercury vapor provided direct, quantitative evidence for quantized energy absorption by atoms, thereby supporting the nascent quantum theory. He details the experimental setup and findings that demonstrated discrete energy levels within the mercury atom, observable through the characteristic spectral lines emitted when electrons excited these levels.

The lecture explains how varying the accelerating voltage applied to electrons bombarding mercury vapor revealed specific voltages at which the electrons' energy was not efficiently transferred to the mercury atoms. This loss of energy corresponded to the excitation of mercury atoms to distinct, quantized energy states. The subsequent emission of light at specific wavelengths from these excited atoms confirmed these energy quanta. Readers gain a direct account of a pivotal experiment that validated quantum mechanics through precise empirical observation.

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Key concepts

Quantized energy levels — Atoms possess discrete, specific energy values rather than a continuous spectrum of possible energies.
Electron excitation — Electrons colliding with atoms can transfer energy, promoting atomic electrons to higher energy states.
Spectral lines — The emission of light at specific wavelengths by excited atoms, corresponding to the energy differences between their quantized levels.
Ionization — The process where an atom loses an electron, typically requiring significant energy input.