Nikola Tesla, His Work and Unfulfilled Promises Page 3

tures, could not be operated on the circuits then existing.

Like Edison's three-wire system, the rotating field must have been obvious when changed conditions called for its application, but in 1888 it was not what was wanted. As Swinbourne said at the time ("Electrician," Vol. 21, p. 342): "The low efficiency is not at all the chief objection to the scheme. The whole arrangement is impracticable, as it demands special alternate-current generators and leads. Until Mr. Tesla can produce a motor which will work on alternate-current circuits as they are, and do that efficiently even with varying loads and without difficulty in starting, he can hardly be said to have solved the problem." The achievement of the Tesla and Ferraris publications was not the solution of a problem presented by existing conditions. They assumed non-existent and, at that time, impracticable conditions, and then applied the obvious principle of the rotating field of Bailey and Deprez. Had not experience subsequently proved the polyphase generator more efficient than the single phase, the rotary field of Tesla and Ferraris, like that of Bailey and Deprez, would never have become of more than academic interest.

In time the polyphase generator did prove its superiority per se, and brought polyphase motors of different types with it into commercial use. But engineering to-day owes Tesla no more than it owes Ferraris, Deprez or Bailey, for Tesla never produced a commercially successful motor. As the demand for polyphase motors gradually came into existence he worked hard to produce a commercial motor, but it did not appear in the market. The motors of the so-called fundamental patents failed absolutely to meet commercial conditions. Though the later Tesla patents describe multitudinous modifications, Tesla himself, with practically unlimited means at his disposal, seems to have failed to produce a commercial self-starting motor for power purposes. Undoubtedly Tesla's theory of magnetic laws, as shown in some of his patents depending on so-called magnetic screening and on reducing iron losses by removing the iron, was an important factor in his failure. But other engineers equally failed to reduce those patents to practice, although on one occasion, according to the sworn testimony of a prominent engineer, $100,000 was offered if he would make the Tesla motor operate successfully.

Two widely different classes of alternating-current motors are in general commercial use to-day. They are known as synchronous motors and induction motors. The two differ radically in principle of design, in theory of operation, in method of manipulation, in the necessary accessory apparatus and in adaptability to different kinds of work.

The synchronous motor is simply an alternating-current generator with its function reversed. The same machine, with no change whatever, runs equally well as generator or motor. This is true of either single phase or polyphase. The polyphase generator is two or more single-phase machines wound on the same frame, and the same is true of the polyphase motor. When the eléctrical world had polyphase machines given it, and was told that alternating-current generators, like direct-current generators, were reversible, it knew all that was necessary for the successful operation of polyphase synchronous motors. And it had the machines (United States patent, No. 218,520, Gramme; "Electrician," October 28, 1882, p. 565; Gordon's dynamo electric machine) and it