The Tesla Coil at 135: Why Nikola Tesla's 1891 Patent Still Matters

In 1891, a Serbian-American inventor sitting in a laboratory on Grand Street in Manhattan patented a circuit that produced high-voltage alternating current at radio frequencies. One hundred and thirty-five years later, that circuit is still inside everything from your car ignition to MRI scanners to the S.E.A.D. System. This is the foundational piece of physics that started the entire 130-year lineage of electromedicine. Here is what Tesla actually invented, how it works, and why it still drives frontier biophysics today.

What Tesla actually invented

The popular image of Tesla — wild electrical arcs, mad-scientist hair, lightning shooting from his fingertips — has obscured something simpler and more important. The Tesla coil is a resonant transformer. That is its defining engineering description. The dramatic visuals are a side effect.

Here is what the 1891 patent (U.S. Patent No. 454,622, "System of Electric Lighting") covers. Two electrical coils — a primary with relatively few turns of thick wire, and a secondary with many thousands of turns of fine wire — are tuned to the same resonant frequency. A spark gap interrupts the primary circuit at that frequency. Energy oscillates back and forth between the two coils via mutual inductance, and the voltage builds up in the secondary to extraordinary levels — typically hundreds of thousands of volts, sometimes millions.

Two properties of this output make it unique. First, the voltage is enormous — orders of magnitude higher than what a conventional transformer can produce. Second, the frequency is high — radio-frequency range, typically 100 kHz to several MHz, far above the 60 Hz of household power. The combination is the key.

Why high voltage at radio frequency is special

Most of what we think of as "electricity" in daily life — wall outlets, household appliances, even most industrial equipment — operates at low frequencies, 50 or 60 Hz. At those frequencies, electricity behaves the way we intuitively expect: it flows through wires, gives a sharp shock if you touch it, and gets stopped cleanly by insulators.

At radio frequencies, electricity behaves differently. High-frequency current does not penetrate deeply into conductors — it flows on the surface (the "skin effect"). It can pass through the human body with minimal physiological effect, even at very high voltages, because the energy is too high-frequency to trigger nerve depolarization. It can ionize gases that would not ionize at low frequencies. It can be radiated as electromagnetic waves.

Tesla discovered all of this in 1891. He could pass current at 200,000 volts through his own body without harm because the frequency was high enough that his nerves did not respond. He could light fluorescent tubes wirelessly across his laboratory. He could ionize gases at a distance. This is why his demonstrations looked like magic — the physics was genuinely different from anything anyone had seen before.

Tesla's own electrotherapeutic claims

What is less well known is that Tesla himself believed his coil had therapeutic applications, and he wrote about them publicly. His 1898 paper, "High Frequency Oscillators for Electro-Therapeutic and Other Purposes" — preserved in PubMed under PMID 29693867^[1] — describes years of personal experimentation with high-frequency currents on the human body.

"For nearly four years, I have been steadily engaged in pursuing this experimental investigation in this department of electricity, and in this period I have observed quite a number of phenomena, suggesting that probably the most important practical applications of the work I am here referring to will be in the treatment of disease."
— Nikola Tesla, 1898

Tesla reported subjective effects on himself and his collaborators: improved sleep, increased appetite, a sense of warmth, occasional reduction of pain. He was careful to note that he was reporting observations, not claims of cures. He was conducting honest frontier science in the 1890s sense — describing what he saw and inviting others to investigate.

This is the part of Tesla's legacy that mainstream physics has largely forgotten. His electrotherapeutic work was peer-reviewed in 1898 by the standards of his era. It was published in The Electrical Engineer. It influenced an entire generation of physicians and inventors — including Georges Lakhovsky in Paris and, eventually, Antoine Priore in Bordeaux. The Tesla coil was the founding instrument of what would become a 130-year scientific lineage.

The modern descendants

If you read Tesla's 1891 patent and look around your modern life, the descendants are everywhere:

• Radio — Tesla's resonant circuit is the foundation of every radio transmitter ever built. His original patent for radio (granted posthumously by the U.S. Supreme Court in 1943) covered the same resonant transformer architecture.
• Neon lighting and fluorescent tubes — Every neon sign on every street uses a high-voltage ballast that is a direct descendant of the Tesla coil. The 1891 patent literally describes lighting gas-filled tubes wirelessly.
• Plasma globes — The novelty plasma balls in science museums are miniature Tesla coils driving noble gas plasma inside a glass sphere.
• MRI scanners — Magnetic resonance imaging uses resonant RF coils operating on the same physics Tesla described. Modern MRI is impossible without Tesla's resonant circuit theory.
• Medical diathermy — Continuously used in physical therapy since the 1920s, diathermy machines are essentially Tesla coil descendants, using high-frequency current to produce deep tissue heating.
• Wireless power transmission — Modern wireless charging pads (Qi standard) use the same resonant inductive coupling Tesla patented.

The 2024 literature review of PEMF therapy in PMC11506130^[2] traces the entire mechanistic lineage of resonant electromagnetic medicine back to Tesla's foundational circuits. The 2025 paper on resonant convergence in biological systems^[3] revisits Tesla coil-style broad-spectrum fields specifically.

Why the Tesla coil drives Tesla BioLights

The S.E.A.D. System uses a Tesla coil for a specific physics reason: it is the only practical way to ionize noble gases without electrodes.

Standard fluorescent tubes ionize their internal gas using metal electrodes sealed into the ends of the glass. The electrodes carry current into the tube and arc through the gas. This works, but it slowly degrades the electrode material into the gas, contaminating the spectrum and shortening the tube's life.

A Tesla coil ionizes the gas through the glass. The high-frequency electromagnetic field of the coil reaches through the sealed glass envelope and excites the noble gases inside via electromagnetic induction — no electrodes required. The plasma tubes in Tesla BioLights are completely sealed, completely pure, and can be re-energized indefinitely without degradation.

This is also why the spectrum is so clean. With no electrode metals contaminating the gas, the emission lines are pure noble gas spectra — the precise wavelengths described in yesterday's essay on noble gases, exactly matching what the photobiomodulation literature has identified as biologically active.

The lineage continues

Tesla's 1898 paper invited others to investigate the electrotherapeutic applications he had glimpsed. Within twenty years, Georges Lakhovsky was building the multi-wave oscillator in Paris. Within fifty, Antoine Priore was building his state-funded plasma device in Bordeaux. Within eighty, Fritz-Albert Popp was measuring biophotons in Germany. Within a century, Michael Levin's lab at Tufts was demonstrating the bioelectric code in peer-reviewed top-tier journals.

Each pioneer built on the one before. Each used some version of Tesla's foundational circuit. The 130-year lineage is not metaphor — it is a literal genealogy of engineering descendants, all the way back to one Serbian-American inventor in a Manhattan laboratory in 1891.

Tomorrow: Georges Lakhovsky and the Multi-Wave Oscillator — the chapter that took Tesla's coil from physics to physiology.

How this thread reaches the rest of the Journal

The Tesla circuit, the noble-gas plasma it drives, and the pulsed electromagnetic field it produces each have their own subsequent essay in this Journal. Day 14 (the inert pharmacology of noble gases) covers the argon, neon, xenon, and krypton inside the tubes — their NMDA-receptor binding, HIF-1α neuroprotection, and TREK-1 channel pharmacology. Day 13 (the 600–1100 nm optical window) covers the photobiomodulation wavelengths the plasma emits. Day 12 (Mitochondria as Light Antennae) covers the cytochrome c oxidase target. Day 15 (the vagal path) covers the parasympathetic engineering of a session. Day 16 (the quantum floor of biology) closes the loop on why the underlying physics is licensed by mainstream science.

Where to read further

The full Tesla coil mechanism — primary/secondary coil tuning, resonant frequency calculations, modern plasma tube specifications — is at our science page. The full 130-year lineage from Tesla through Levin is at the lineage page. The peer-reviewed sources Tesla's 1898 paper sits alongside today are at PubMed under PMID 29693867.