Tesla: The Life and Times of an Electric Messiah by Nigel Cawthorne Page A

be better to use an AC current. While a circuit interrupter would only give a frequency of, at best, a few hundred cycles per second, an alternator could give 10,000 or 20,000 cycles per second. However, once an alternator reached that speed it began to fly apart, but higher frequencies could be generated electrically.
    He had already used induction coils and capacitors – electrical storage devices such as a Leyden jar – to give split-phase AC currents to run his motors. These could also be used to increase the frequency even higher. Putting a connecting capacitor across the terminals of a coil produced a circuit that resonated, giving a spike in output. He called this the oscillating transformer, though other experimenters began calling it the Tesla Coil. A coil coupled to a capacitor that resonates at a specific frequency is the basis of all wireless transmission.
    Refining his oscillating transformers, he earthed one terminal to the city’s water main, he moved around New York detecting the electromagnetic waves generated at various frequencies. Abandoning Hertz’s primitive spark gaps, he used other tuned circuits and vacuum tubes as detectors. However Tesla’s aim was not to transmit an intelligible signal as we use radio waves now. His goal was the wireless transmission of power.
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    The Skin Effect
    Early in these experiments, Tesla accidentally touched a high-voltage terminal and, to his surprise, was unhurt. At high frequencies, electricity exhibits what is known as the ‘skin effect’. The magnetic field created pushes the current to the outside of a conductor, so it does not run through the body, damaging the nerves and muscles. Instead it travels across the surface, leaving the internal structure undamaged. In his public demonstrations, he touched one terminal of a high-frequency apparatus generating tens of thousands of volts and illuminated a bulb or tube held in the other hand. This also showed that alternating current, if at a sufficiently high frequency, was safer than direct current.
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    On the Road
    Tesla and his lectures hit the road in 1893, and pulled in huge audiences with his dazzling demonstrations and novel ideas. In Philadelphia, he outlined a method of transmitting pictures – that is, television. The secret of wireless transmission, he said, was resonance. Wires become unnecessary as electrical impulses jump from a sending device to a receiver if they are tuned to the same frequency, and he presented a diagram showing aerials, transmitters, receivers and earth connections, all the elements of a modern broadcast system.
    This was not just theory. He gave practical demonstrations. On one side of the stage he had a high-voltage transformer connected to a bank of Leyden jars, a sparking gap, a coil and a length of wire hanging from the ceiling. On the other side was an identical length of wire and an identical coil and bank of Leyden jars. But instead of the sparking gap there was a Geissler, or discharge tube that glowed when electricity was passed through it, like a primitive neon light.
    Not only was the demonstration dazzling, it was full of strange sounds. When electricity was fed to the transformer, the core strained, making odd groaning sounds. Corona sizzled around the edges of the foil on the Leyden jars and sparks cracked across the sparking gap. But the radio waves travelled noisily from one antenna to the other and the Geissler tube lit up.
    Tesla was advised to play down the possibilities of his wireless system. It seemed so fanciful it might deter conservative businessmen who might otherwise be interested in his motors or his lighting systems. Nevertheless, he said, it earned him the title of ‘Father of the Wireless’ among fellow researchers. Others had investigated the phenomenon of wireless transmission before him, but Tesla had pioneered the use of the tuned circuit, the aerial and the ground connection . He was giving these