Dr. NIKOLA TESLA

by W. H. Eccles

Nikola Tesla, who died on January 7, was born in 1857 at Smiljan in Croatia. His father, a Serb, was a clergyman of the Greek Church; his mother is remembered as very inventive and is credited with making improvements in churns, looms and other rural machinery. Nikola, while at school, began to make electrical experiments, and finished his formal education in the engineering faculty of the Graz Polytechnic School. After a period in the Government telegraph department at Budapest, he joined the Edison concern in Paris and went to the, United States about 1883. Here he worked under Edison for a time, but soon set up his own firm for the manufacture of arc lighting plant.

At this period the applications of electric power in industry were effected mainly by direct current, but many inventors were attacking the problem of making motors suitable for use with alternating current. Tesla in the United States and Ferraris in Italy each published in 1888 the results of several years of independent work on motors utilizing rotating magnetic fields produced by two-phase currents. Both inventors envisaged machines in which the rotor is propelled asynchronously by means of currents induced in it by the rotating field, and Tesla described also motors in which the rotor is pulled round in synchronism with the rotating field. Neither type need employ brushes or commutators. These rotating-field motors, together with the introduction of polyphase currents, proved to be the solution of the problem of using alternating current in factories. In addition, by 1890, Tesla also invented methods of starting and running motors on single-phase current. His designs were so sound that his larger machines attained efficiencies of 95 per cent. Having completed his task, he disposed of his patents to the Westinghouse Company and dropped the subject.

Hertz's work was directing attention to high-frequency alternating currents, so Tesla turned to the problem of generating these currents on an engineering scale. First he designed and built a succession of alternators, and by 1891 attained a frequency of 30,000 cycles per second. He studied the properties of these currents in circuits possessing distributed inductance and capacitance, and developed tuned coupled circuits for enhancing their voltage by resonance. For higher frequencies he employed the discharge of condensers through induction coils, obtaining big powers by aid of rotating dischargers or magnetic blow-outs at the spark gap. On coupling the primary circuit to a resonant secondary circuit comprising metal areas, large flaming and streaming ionization currents were obtained in air and in Geissler tubes. Ionic bombardment was observed to produce brilliant phosphorescence, and sometimes fusion, of solid matter.

But Tesla's main purpose was the transmission of power and messages across space. In 1892 and 1893 he developed his scheme. High-frequency power was to be led to a large antenna consisting of an elevated metal area connected by a vertical wire to a large metal plate buried in the earth. The receiving antenna was to be equal in every respect. The figure in the Journal of the Franklin Institute shows the source of oscillations connected into the vertical wire near the earth at the sending station, and the receiving apparatus in the corresponding place at the receiving station. He did not patent the antenna. Tesla states his belief that the electrical oscillations will be propagated along the surface of the earth and that they may be assisted by an upper conducting layer of the atmosphere--this is eight years before Heaviside and Kenelly. Tesla had thus supplied, two years before wireless began its commercial career, all the elements of both spark and continuous wave sending stations. For the receiving station the Lodge or Branly coherer was already available for spark telegraphy, but Tesla concentrated on continuous waves because he was more interested in the transmission of power than in the transmission of messages. After building one or two small stations, he started in 1897, at his own expense, a station of 200 kilowatts in Colorado. From this point in 1899 he transmitted power enough to light a lamp at 30 km. For the reception of continuous wave signals he invented the interrupter device known as a ticker, which was employed by others for the next dozen years, and from the Colorado station received signals at a distance of 1,000 km. Later, his form of antenna, his rotating discharger, and his tuned transformer were used successfully by many others at spark stations in every country.

Space limits this survey to a few of the new things which Tesla's creative imagination and constructive genius gave to the world. His other inventions include pyro-magnetic generators, thermo-magnetic motors, unipolar dynamos, meters, lamps, mechanical vibrators of huge power and a variety of instruments. Some seven hundred patents stand in his name, mostly taken out before he was fifty years of age. Apparently his method of work was to state a problem, devise solutions, build machines and file a patent specification or, possibly, read a paper to a technical society. Then he would start on a new problem. It happened that one of his subjects, high-frequency discharge, made a brilliant display, and he was persuaded to lecture upon it several times. The demonstrations were perfect and very showy; consequently sober folk concluded that Tesla was somewhat of a showman. This is quite wrong. Throughout his long life of eighty-five years, Tesla seldom directed attention to his own successes, never wrote up again his old work, and rarely claimed priority though continually pirated. Such reserve is especially striking in a mind so rich in creative thought, so competent in practical achievement.