In 1887, the German physicist Heinrich Hertz demonstrated the existence of electromagnetic radio waves at the Technische Hochschule in Karlsruhe, Germany. Using a spark-gap oscillator to generate high-frequency electrical oscillations and a simple wire loop as a receiver, Hertz showed that invisible electromagnetic waves traveled through space at the speed of light, confirming Maxwell's theoretical prediction. These experiments in Karlsruhe proved that light, heat, and radio waves were all forms of the same electromagnetic radiation, fundamentally changing the understanding of the physical world.

Hertz's discovery that invisible electromagnetic waves constantly surround and pass through us without our awareness became a powerful metaphor for the unseen forces, emotional, historical, and spiritual, that pervade literary modernism. The idea that an entire world of waves existed beyond human perception resonated with the Symbolist movement's belief in a reality behind appearances and with the modernist conviction that language itself operates through invisible frequencies and resonances. Rilke, who was deeply interested in contemporary science, likely drew on such concepts in his exploration of the invisible dimensions of experience in the "Duino Elegies."