Nikola Tesla, His Work and Unfulfilled Promises Page 2

ported, previously proposed to wobble the earth's charge for man's ignoble uses, but he now, if these things can be taken seriously, has designs on the universe. The price of copper remains in the neighborhood of 11 cents, however." In 1900, a description of a Tesla patent which if practicable would revolutionize the electrical industry, is printed without one word of editorial comment. ("Electrical World," Vol. 35, p. 792.)

Tesla's career, since the time he first stepped into prominence by his lecture before the A. I. E. E. in 1888, naturally divides itself into three periods, which may be designated as the rotary field or patent period, the high voltage and high frequency or lecture period, and the present or newspaper period. It will be well to consider these separately in an endeavor to arrive at a just estimation of the man's work and of the value of his contributions to the engineering or scientific world.

Prior to 1884, the alternating current system of distribution, though older than the direct current system, was in little use. Gramme had taught the world how to build a satisfactory direct current commutator. Direct current seemed to have all the advantages of alternating current and would perform many services for which the latter was not suitable, notably electrolytic work. But in '83 and '84 Gaulard showed that the well known Ruhmkoff coil could be used to transform alternating current from high to low voltage, permitting of great economy in line wire, and he built and operated his transformer for lighting.

In 1885 Zipernowski & Deri produced a transformer of high commercial efficiency, and showed how to obtain excellent regulation, impossible with Gaulard's series system, by proper connection of the primaries in parallel.

From this time alternating current began to be more used for electric lighting. One of the objections to the system was that there were no small self-starting motors that wou.d operate efficiently on it. Accordingly, when Tesla announced, in May, 1888, that he had solved this motor problem, he at once became one of the most prominent figures in the engineering world. His solution was a theory of the combination of two or more alternating currents of different phase to produce a resultant rotating magnetic field. This same theory had been published in Italy a few weeks prior to Tesla by Ferraris. ("L'Elettricita," April 22, 1888.) Ferraris, however, contented himself with publication of the theory, while Tesla patented it, and followed up his first patents with a mass of other patents describing every conceivable construction and mode of operation that could in any way be imagined to embody his rotating magnetic field. It is for this reason that the rotating field theory is associated in this country with the name of Tesla rather than with that of Ferraris, although the contrary is the fact in every other country.

The idea of a rotating magnetic field as the resultant of two currents was not novel. It had been produced by Bailey ("Phil. Magazine," October, 1879) in 1879 with commutated direct currents, and by Deprez ("La Lumiere Electrique," December 8, 1883) in 1883 with alternating currents. It is scarcely conceivable that the application of these experiments would have escaped the eyes of the engineering world when the greater efficiency of polyphase alternators over single-phase alternators forced the former into general use. But that time had not come in 1888, and the motors described by Tesla, even if they had been commercially efficient struc-