Favorite experiment

One of my favorite physics experiments was conducted by Thomas Young (1773-1829) when he demonstrated that light consists of waves by showing that the distribution of brightness by interfering beams could be explained by the additive and subtractive interference of the wavefronts. Young´s experiment, performed in the early 1800s, played a vital role in the acceptance of the wave theory of light, defeating Isaac Newton´s corpuscular theory which had been the accepted model of light propagation at that time. Although, a later observation by Heinrich Hertz (1857-1894) demonstrated that under different circumstances, the photoelectric effect can cause light to behave as if it is composed of discrete particles. These seemingly contradictory discoveries made it necessary to go beyond classical physics and eventually consider the quantum nature of light.