Victorian Inventions by Leondard De Vries, American Heritage Press (McGraw Hill) 1971
Tesla's Experiments with Alternating High Voltage Currents
While in Europe alternating currents with frequencies not exceeding 100 per second were still being studied eagerly for practical applications, reports were received from America in 1891 that most surprising experiments were being carried out there with alternating currents of 15,000 cycles. The initiator of these studies was a Hungarian employed with the Westinghouse Company - Nicola Tesla. With remarkable talent he has conducted experiments and research in a hitherto almost unexplored field: that of alternating currents of extremely high voltage and frequency. He gave an account of his work before the American Institution of Electrical Engineers in New York in a lecture which has since become famous. It made an indelible impression upon the audience, both on account of the brilliant experiments and the completely new vistas it has opened. His work places Tesla among the greatest of our present-day scientists and inventors such as Edison, Graham Bell and Thomson.
When the news of Tesla's experiments reached Europe, he was approached by the most prominent scientific circles in Britain and France who invited him to repeat his experiments in those countries. These lectures were attended by large and enthusiastic audiences which included men of great authority in the fields of the theoretical and applied sciences. After three hours of lecturing to an enthralled and fascinated audience, Tesla was compelled to admit that he had discussed only part of his research work.
Tesla uses two different types of equipment for generating his alternating high-frequency currents. One is a dynamo with 384 wire coils and an equal number of field magnets rotating at 50 revolutions per minute, thus producing an alternating current of 50x384=19,200 cycles per second. Tesla also uses a special type of transformer. Its primary coil has only a few windings and is connected in series with a spark-gap, a condenser and the secondary winding of a Ruhmkorff-type induction-coil. With the second combination, tensions of half a million volts and scores of thousands of cycles per second can be generated, producing most impressive discharge phenomena in the open air and in glass tubes filled with rarefied air.
In the air, these currents engender electrical fireworks of unprecedented splendor which assume the weirdest shapes, forming luminous fans and plumes of gossamer-like texture. Amazingly enough, these ultra-high voltages are in no way dangerous, thanks to their high frequency. In Berlin, Tesla placed himself between two of his assistants who were almost 15 feet apart, each of them touched one pole of the high-voltage transformer, and when Tesla reached out to them with his two arms, wavy bundles of violet-coloured electric fire shot forth from his fingertips, spreading out to one assistant's hand and to the other's forehead. This to the great dismay of some of the spectators, until they noticed that the experiment was harmless and painless!
One of Tesla's most striking experiments was his demonstration with the 3-foot-long Geissler tubes. For that purpose, two metal bars, 10 feet in length, attached to the floor and ceiling, were connected to the poles of his high-voltage transformer. When Tesla moved two Geissler tubes into the field between the two bars, they became luminous over their entire length without being connected either to the metal bars or to the transformer. In the words of one reporter: “Tesla stood there like the archangel, brandishing the flaming sword!”
