In 1917, Nikola Tesla built a remarkably advanced machine so ahead of its time that it could break and reconnect a 50-horsepower electrical load at a staggering 100,000 cycles per second. But this wasn’t done with semiconductors or digital circuits. Tesla used a spinning cogwheel dipped in mercury, physically opening and closing the circuit rhythmically. This mechanical interrupter pulsed 50,000 volts of direct current into massive capacitor banks and a conical Tesla coil, which could send electrical arcs shooting across the room several feet long.
This wasn’t sci-fi. It was Tesla proving that wireless energy transmission was possible. He dreamt of power without wires and actually built the hardware to make it happen. Yet, after this breakthrough, the world went silent. There were no venture capitalists storming his door, no viral tech stories, no global summits. Instead, Tesla’s notebooks and machines were largely forgotten, buried beneath decades of copper cables and industrial inertia.
Fast forward to today, and the same physics Tesla worked on—guided surface waves, also known as Zenneck waves, traveling with minimal losses along the Earth’s surface—are now being explored with modern science. These waves are real; researchers have measured, modeled, and recreated them. What Tesla did manually with his mercury interrupter and Tesla coils is now being done with contemporary techniques.
Back then, Tesla’s mercury interrupter was a state-of-the-art high-frequency switching device, predating silicon rectifiers and offering efficient rectification through the formation of vacuum bubbles in mercury arcs—a method still admired though replaced by silicon diodes today. Interestingly, Siemens sent one of their first commercial mercury rectifiers to Tesla as a tribute before his death in 1943. Tesla’s grateful reply commended Siemens for giving him credit for his foundational inventions. Original letters documenting this exchange are preserved in museums in Florida and Pittsburgh.
Tesla’s detailed papers, schematics, and patents on mercury interrupters and high-frequency systems survive in archives like the Tesla Collection and his Colorado Springs notes. These documents shed light on the technical mastery behind his wireless power experiments. Today’s research into wireless power takes inspiration from Tesla’s legacy. Far from a forgotten dream, Tesla’s work was simply ahead of its time—and now, finally, the world is ready.