Transverse Waves Vs. Longitudinal Waves: Nikola Tesla’s Discovery
In 1864, James Clerk Maxwell wrote a paper titled “A Dynamical Theory of the Electromagnetic Field,” and put forth equations theorizing the unification of electric and magnetic fields which react to one another creating electromagnetic waves. His theory of electromagnetism proposed that these EM waves were transverse (waves that oscillate perpendicularly to the propagation of travel), and that there must be a medium in nature with solid properties or else these transverse waves would be impossible. It was proven prior to Maxwell by many scientists that transverse waves cannot travel through gas or water because there is no force preventing it from falling apart. The old theories stated that there must be a force perpendicular to the propagation of the wave which maintains its driving strength. This medium was considered the Ether.
It wasn’t until Oliver Heaviside came along in 1885 and noticed that Maxwell’s equations were inconsistent. Maxwell used multivariable/vector calculus which was almost impossible to understand, so Heaviside invented a new form of calculus to reduce Maxwell’s equations. With his new method, Heaviside was able to simplify Maxwell’s equations from 20 to just 4. These 4 equations are still set in stone today (and should technically be called Maxwell-Heaviside Equations).
In 1886, Heinrich Hertz experimentally investigated the existence of electromagnetic waves in order to prove Maxwell’s equations. He used a small spark gap transmitter powered by an oscillator and a new type of receiver, and when his generator was turned on there were sparks emitting in both his transmitter and his receiver. It was obvious that the transmitter must be sending energy of some kind to the receiver. Hertz was able to measure the wavelength and also the speed of the waves which came out to be the speed of light. He also showed that, similar to light, these waves could be reflected. To him, this was absolute proof of transverse EM waves, and with this demonstration the scientific world turned the Maxwell-Heaviside Equations into laws.
Nikola Tesla caught the enthusiasm of Hertz’ findings and repeated Hertz’s experiments with a much improved and a far more powerful apparatus. His new alternating current system of power transmission was already fully developed and with his newly created Tesla Coil, which produced high-voltage, low-current, high frequency alternating current electricity, he was able to progress far beyond the experiments of Hertz and others. Instead of using an electrical interrupter that generated a hundred cycles per second like Hertz, Tesla used 20,000 cycles from his alternator. During this experiment, Tesla noticed that when the sparks were generated, his Geissler tubes (gas discharge tubes similar to neon lighting) lying nearby would light up in unison with the sparks. Later he noticed that the tubes would not light up if they were held at right angles to the terminals of his induction coil. The only time they would light up is if they were parallel to the spark. With these observations, Tesla came to the conclusion that the effects Hertz observed were not due to electromagnetic waves, but were “electrostatic thrusts” (longitudinal waves that oscillate parallel with propagation of travel instead of perpendicularly like transverse waves). If they were transverse EM waves, then the position of the tubes wouldn't have mattered. These observations convinced Tesla that Hertz and all others following his claims were misled because they chose to focus on Maxwell’s theory and failed to recognize that the phenomenon was actually caused by electrostatic effects.
In 1891, Tesla gave a lecture before the American Institute of Electrical Engineers at Columbia College and showcased his new discovery. He politely opposed the views of Hertz (and other scientists like physicist Oliver Lodge) and proposed that EM waves had little to no effect on the phenomenon of light production. Although he agreed that his apparatus gave off some EM waves, he theorized that they were blotted out after they had traveled a short distance from the transmitter. This, he assumed, was because by the time their necessary frequency could be reached, the conductor would become opaque to the passage of the waves. The only reasonable explanation to the cause of the phenomenon was an electrostatic effect. Tesla then went on to demonstrate that these electrostatic waves could be used to light wireless light bulbs before a spell-bound audience.
In 1892, Tesla went to Germany to share his observations with Hertz, but was met with great disappointment from the German physicist. Though, to Hertz’ credit, who wants to hear that they may have been wrong after making one of the greatest discoveries in the history of science.
This was an important part in Tesla’s life. He was literally at a crossroads in the history of energy transmission. Others chose to follow Maxwell’s path while Tesla chose to go his own direction. He had discovered something that even Maxwell failed to predict. Tesla chose to progress with his new discovery of electrostatic energy, a discovery that even today we have yet to fully comprehend.
Throughout the mid 1890s, Tesla experimented with x-rays and the wireless transmission of energy sending signals as far as 30 miles, and always came to the same conclusions as he did in the early 1890s--that he was working with longitudinal waves and not transverse EM waves. Furthermore, in 1900, after evolving his Magnifying Transmitter which allowed him to produce EM activities of many millions of horse-power, Tesla made one last desperate attempt to prove that the disturbances coming from his oscillator were EM waves similar to light, but again failed to do so. This forced Tesla to question the validity of Maxwell’s theory.
Nikola Tesla came to a final conclusion that the EM waves used in the wireless transmission of energy, and all other electromagnetic radiation, are not transverse waves, but instead are waves similar to sound with longitudinal properties. Since Maxwell’s solid ether theory was incorrect, and it is well known that light is dependent on a medium which limits it to a constant velocity, Tesla believed that the medium must have gaseous properties with density and elastic force. In Tesla’s own words, “light cannot be anything else but a longitudinal disturbance in the ether, involving alternate compressions and rarefactions. In other words, light can be nothing else than a sound wave in the ether.”
“The history of science shows that theories are perishable. With every new truth that is revealed we get a better understanding of Nature and our conceptions and views are modified. Dr. Hertz did not discover a new principle. He merely gave material support to a hypothesis which had been long ago formulated. It was a perfectly well-established fact that a circuit, transverse by a periodic current, emitted some kind of space waves, but we were in ignorance as to their character. He apparently gave an experimental proof that they were transversal vibrations in the ether. Most people look upon this as his great accomplishment. To my mind it seems that his immortal merit was not so much in this as in the focusing of the investigator’s attention on the processes taking place in the ambient medium. The Hertz-wave theory, by it fascinating hold on the imagination, has stifled creative effort in the wireless art and retarded it for twenty-five years. But, on the other hand, it is impossible to over-estimate the beneficial effects of the powerful stimulus it has given in many directions.” NT- (“The True Wireless.” Electrical Experimenter, May, 1919.)
The Maxwellian interpretation of EM waves is now generally accepted as scientific fact, and even currently taught in most academic physics and engineering textbooks. However, Tesla’s work challenging this theory certainly warrants further study into this area. First, Tesla’s experiments were far more in-depth than his colleagues’ work, as well as utilizing more advanced equipment to conduct the experiments themselves. Secondly, he provided solid and sufficient empirical evidence concretely refuting Maxwell’s theory. Based on this, Tesla’s groundbreaking work should at a minimum be acknowledged in today’s world, and certainly further explored.
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