POLYPHASE CURRENTS.

5

own inventions to develop, Mr. Tesla could long remain in eventhe most delightful employ; and, his work now attracting atten-tion, he left the Edison ranks to join a company intended tomake and sell an arc lighting system based on some of his inven-tions in that branch of the art. With unceasing diligence hebrought the system to perfection, and saw it placed on the market.But the thing which most occupied his time and thoughts, how-ever, all through this period, was his old discovery of the rotatingheld principle for alternating current work, and the applicationof it in motors that have now become known the world over.

Strong as his convictions on the subject then were, it is a factthat he stood very much alone, for the alternating current hadno well recognized place. Few electrical engineers had everused it, and the majority were entirely unfamiliar with its value,or even its essential features. Even Mr. Tesla himself did not,until after protracted effort and experimentation, learn how toconstruct alternating current apparatus of fair efficiency. Butthat he had accomplished his purpose was shown by the tests ofProf. Anthony, made in the of winter 1887-8, when Tesla motorsin the hands of that distinguished expert gave an efficiency equalto that of direct current motors. Nothing now stood in the wayof the commercial development and introduction of such motors,except that they had to be constructed with a view to operatingon the circuits then existing, which in this country were all ofhigh frequency.

The first full publication of his work in this direction—outsidehis patents—was a paper read before the American Institute ofElectrical Engineers in New York, in May, 1888 (read at thesuggestion of Prof. Anthony and the present writer), when heexhibited motors that had been in operation long previous, andwith which his belief that brushes and commutators could bedispensed with, was triumphantly proved to be correct. Thesection of this volume devoted to Mr. Tesla’s inventions in theutilization of polyphase currents will show liow thoroughly fromthe outset he had mastered the fundamental idea and applied itin the greatest variety of ways.

Having noted for years the many advantages obtainable withalternating currents, Mr. Tesla was naturally led on to experi-ment with them at higher potentials and higher frequencies thanwere common or approved of. Ever pressing forward to deter-mine in even the. slightest degree the outlines of the unknown, he