Analysis of Hertz's Experimentum Crucis on Electromagnetic Waves [Historical Corner]

In this article, we examine one of Heinrich Hertz's (1857-1894) experiments: a measurement for the interference of electromagnetic waves in air (the experimentum crucis). This experiment showed, for the first time, that electromagnetic waves exist in free space and travel with finite velocity, as predicted by Maxwell's equations. To carry out the experiment, Hertz invented the first transmitter and receiver of radio waves. We use results from theoretical analysis to explain the physics behind his apparatus-how it worked. Our comparison of the theoretical results with his measurements shows the accomplishments as well as the limitations of the latter. We also describe the role of his contemporaries in providing explanations for his results and repeating and improving his measurements.