Decision in Favor of the Tesla Rotating Magnetic Field Patents

As announced in these pages last week, Judge Townsend in the U. S. Circuit Court for the District of Connecticut has handed down a decision sustaining three broad Tesla patents — Nos. 381,968, 382,279 and 382,280 — of May 1, 1888, in the suit of the Westinghouse Electric & Manufacturing Company against the New England Granite Company, which had been using a Cushman phase motor operated from a General Electric three-phase generator. The case was reviewed at considerable length in the ELECTRICAL WORLD AND ENGINEER of Nov. 18, 1899, when the chief points in contention were brought out. The full text of the decision has now been handed down, which follows closely the lines then noted.

The claims in issue in patent No. 381,968 are as follows:

"1. The combination, with a motor containing separate or independent circuits on the armature or field-magnet, or both, of an alternating-current generator containing induced circuits connected independently to corresponding circuits in the motor, whereby a rotation of the generator produces a progressive shifting of the poles of the motor, as herein described.

"3. The combination, with a motor having an annular or ring-shaped field-magnet and a cylindrical or equivalent armature, and independent coils on the field-magnet or armature, or both, of an alternating current generator having correspondingly independent coils, and circuits including the generator-coils and corresponding motor-coils in such manner that the rotation of the generator causes a progressive shifting of the poles of the motor in the manner set forth."

That of patent No. 382,280 is as follows:

"1. The method herein described of electrically transmitting power, which consists in producing a continuously progressive shifting of the polarities of either or both elements (the armature or field-magnets or magnets) of a motor by developing alternating currents in independent circuits, including the magnetizing coils of either or both elements, as herein set forth."

The claims in issue of patent No. 382,279 are as follows:

"1. The combination, with a motor containing independent inducing or energizing circuits and closed induced circuits, of an alternating-current generator having induced or generating circuits corresponding to and connected with the energizing circuits of the motor, as set forth...

"2. An electro-magnetic motor having its field magnets wound with independent coils and its armature with independent closed coils, in combination with a source of alternating currents connected to the field coils and capable of progressively shifting the poles of the field magnet, as set forth.

"3. A motor constructed with an annular field magnet wound with independent coils and a cylindrical or disk armature wound with closed coils, in combination with a source of alternating currents connected with the field-magnet coils and acting to progressively shift or rotate the poles of the field, as herein set forth."

The complainant's theory of the invention was that the gist of it was the utilization of the alternating currents generated by an alternating-current dynamo or generator for effecting such shifting of the magnetic poles or resultant attractive forces upon the armature of a motor, and thus causing such armature to rotate in response thereto. His broad invention was the production in a motor of a progressively shifting magnetic field (or pole) by means of two or more independent alternating currents, differing in phase, and circuits which preserve the independent character and phase relation of such currents."

By way of defence, the decision goes on, the defendants relied upon four prior publications, namely, the Baily article of 1879; the Siemens patents of 1878; Deprez's article of 1880-4, and the Bradley application of May 9, 1887. As to Baily the court says: "Baily merely showed how to apply a series of successive impulses to the disk by an intermittent rotation of the field and thus produce Arago's rotation field with stationary magnets instead of a moving magnet, and he showed how the motion of the disk could be reversed. He conceived the idea of a uniform rotation by a manifestly impossible and impracticable construction. He did not claim to have established a continuous rotating field or to know any way in which a uniform rotation could be produced. He did not use alternating currents, but reversed currents. He was not dealing with the subject of the transmission of power. Defendants' expert admitted that his paper merely describes a laboratory experiment."

As to the allegation that the Siemens patent of 1878 was an anticipation, the Court says: "This patent is chiefly for means to convert motive power into electricity. It does not specifically relate to or describe or fully show a system of apparatus for the transmission of power. It not only fails to refer to any difference of phase, or to point out how the armature and overlapping coils are to be coupled together to produce such phase, but it repeatedly describes the use of commutators in order to create a continuous or direct current. At this date it was not known that an alternating current machine could be used as a motor. Motors then were operated only by a direct or continuous current so far as the record shows. The 'suitable modifications' to change this machine into a motor are nowhere described; in view of the repeated reference to commutators, the modifications must be presumed to relate to such continuous current machines; and in view of the then state of the art such suitable modifications would have required such a series of experiments and such a departure from the existing theories and such development and application of devices in unexpected and non-analogous ways as would in themselves have constituted invention. Siemens himself, as late as 1884, and Alteneck, the other inventor of said Siemens patent, in 1881, admitted that they did not know that alternating currents could be used as motors. This evidence was objected to on the ground that the publications containing said statements are not duly proved, but the fact is established by other sufficient evidence."

The Court then takes up the Bradley application filed six months before the Tesla application, but regards it also as inadequate. "The single specific object of Bradley's construction stated in said specification was to obviate 'difficulties and limitations' in prior constructions wherein the machine was idle during a part of the time. He suggests that this may be done by rectifying one of the alternating currents by a commutator and then combining the two or by connecting each with a separate circuit. He does not show how he would use them in the latter case to operate a motor, nor did he indicate any combination of the alternate currents for a single motor or show that he had any conception of their use, if at all, otherwise than separately in single-phase motors.

"A comparison of the Bradley application prior to Tesla with the Bradley patent, issued subsequent to Tesla, shows that in the former he described a method and illustrated an apparatus designed to obviate the objections to a two-phase alternating current by combining both currents in one by means of a transformer, while from the latter he omitted this description and method and inserted figures which, while strikingly suggestive of the apparatus shown by Tesla, failed to show that he conceived the Tesla idea or sought to secure the object of Tesla's invention. For this reason, and further because Bradley's application is limited in scope, and ambiguous and indefinite; because it fails to show that he had any conception of the Tesla idea of 'the utilization of the motor for the purpose of progressively shifting the magnetic poles of a plurality of alternating currents by circuits which preserved the independence and differing time relation of their phases;' because, even if the idea had been first conceived by Bradley, it was not sufficiently described to disclose the principle or method of operation; because Tesla was the first to reduce this principle to practice, Bradley does not anticipate or limit."

As to the publications of Marcel Deprez of 1880-84, the Court concedes that Deprez not only disclosed the principle which Tesla utilized, but he gave a mathematical demonstration of the rotating field. But the only device possible to Deprez's mind was an electric compass. "All that Deprez demonstrated, therefore, was that if a field was made in which the field magnet varied relative to the brushes, or vice versa, the angle of variation would be indicated by the needle in another machine which would move quickly or slowly as the brushes and magnets shifted relative to each other and would indicate the new angle subtended between the brushes and the magnet. The only useful, practical application of this device was to attach it to a machine which would produce currents, and to use the earth or a ship to indicate the shift of position by means of a needle on top of the mast. This apparatus failed to teach any one that alternating currents could be used as a source of power in a motor. It was a mere indicator. It did not involve the utilization of two alternating currents differing in phase as a source of power in producing a continuous magnetic field. It did not depend upon any constant, regular, progressive currents, and, so far as the evidence shows, it was like the apparatus of Baily, confessedly a mere laboratory experiment. That Deprez did not conceive of the Tesla idea of utilizing regular, progressive, constant alternations of current is conclusively shown by his own statement in 1884 after the publication of this paper and after the invention of the Gaulard and Gibbs alternating current systems for lighting, when he published another paper in which he criticised the system and stated that one of the most serious objections to it was that it was not applicable to the transmission of power and adds: 'I must further remark that alternating currents are of no use in the transmission of power; they are suitable only for lighting purposes.' In fine, the evidence shows that, as Prof. Sylvanus Thompson says in his work on this general subject: 'Deprez's theorem bore no fruit; it remained a geometrical abstraction."

Judge Townsend then reviews the state of the art up to the time of Tesla's invention, and says that prior to it no alternating-current motors were in use, although there was an urgent demand for them. Six months later Tesla read his paper before the American Institute of Electrical Engineers and announced that previous efforts to utilize alternate currents had failed; that he had brought forth a novel system for the transmission of power, and explained its theory and demonstrated its operation by exhibiting a working motor; and no one of the electricians present questioned his claim or criticized his apparatus.

Tesla first stated the discovery how these alternations could be thus utilized and showed the machine and method adapted for this purpose. He is entitled to a patent for this discovery as were the discoverers of the use of anthracite coal instead of bituminous coal, or of the hot blast instead of the cold blast, in the manufacture of iron, or of the practical application of electricity to the telegraph or telephone. Judge Blatchford once sustained a patent for insulating electric wires by means of gutta-percha, and said:

"The gist of the invention is the discovery of the fact that gutta-percha is a non-conductor of electricity, and the application of the fact to practical use. The claim is valid, even though a metallic wire covered with gutta-percha existed before the plaintiff's invention, if it was not known that gutta-percha was a non-conductor of electricity, and could be used to insulate the wire."-Colgate vs. Western Union Telegraph Company, 6 Fed. Cases, 86.

It is not necessary to go to this extent in sustaining these patents, The complainant may safely rest its case on the general principles laid down in the various decisions of the Supreme Court and extended and developed in Potts vs. Creager, supra.

Further than this, the Court says: "But if the evidence already considered be disregarded and it should be assumed that alternating and alternated currents were theoretically known equivalents, even then the argument of counsel for defendants does not appear to be sound. They contend that a superior result, by reason of the substitution of one known equivalent for another, does not constitute invention. But the first substitution or application of such theoretical equivalent to produce a new or non-analogous or unexpected result may involve invention. Tesla applied the alternating current to do what the alternated current had never before done, namely, to produce a new, unexpected and practical system of transmission of power. A careful study of the evidence has led to the conclusion that Tesla made a new and brilliant discovery. But even if this be incorrect, it is proved that by a new combination and arrangement of known elements, he produced a new and beneficial result never attained before. The technical defense of non-infringement by reason of the fact that defendants use only a motor, and that there is no allegation or proof of conspiracy with the owners of the plant which supplies the power, was not pressed on the argument, and as six days were spent in the discussion of the questions on the merits this point will not be discussed. If any amendment is necessary to cover these points it should be allowed. The contention of defendants that Tesla does not describe an operative machine is not satisfactorily proved. It is proved that in fact various practical motors have been manufactured according to his invention."

The question was urged by the defense as to the point that "independent" in the patents meant separated or "isolated." The Court held that "the claims, confessedly, cannot be read as requiring isolation of the circuits, but at most only such independence as is necessary for the purpose of producing a rotary field; that is, the connections must be such as not to interfere with the independency of the circuits which operate to shift the poles. The only practical result from defendants' use of three conductors instead of six is an improvement to regulate the action of the motor, which result was anticipated by Tesla, and it is proved that it was known in the prior art that one of these arrangements was a substitute for the other. Inasmuch as the defendants have not invented any new idea, but have adopted an old contrivance which performs the same result in substantially the same way by a formal and unsubstantial change in means, and by circuits which while in some sense interdependent are operatively independent, and which preserve and utilize the vital element, independence of phase, these circuits must be held to be the equivalents of the independent circuits of the patent, the word independent being interpreted to mean comparatively independent, so as to embrace the true spirit and essence of the Tesla invention.

"This conclusion is supported by a great number of illustrations of similar uses of such independent conductors in the general field of the arts. As the expert for complainant has pointed out, in railroads, cash carriers, electric telegraphs, the tracks, the earth or a single wire, will serve as common but independently acting conductors. It does not seem necessary to further discuss this contention based on a technical verbal distinction. Defendants' three wires are operatively independent; they are actually independent while in action; they are independent enough to do the required work."

The Court touched briefly on the action of the Imperial Court of Germany presumed to affect adversely the Tesla patents, but saw no sufficient reason why the conclusion of that court should have any bearing on the question of infringement here.

Infringement of the first claim of patent No. 381,968 necessarily implies infringement of the method patent No. 382,280. The finding that the circuits of the defendants are independent, in the sense of the Tesla patents, is decisive against the defendants as to the infringement of the first and second claims of patent No, 382,279; and the field magnet of defendants' motor, while differing in some respects from that of the third claim of No. 381,968, is annular or ring-shaped within the meaning of said claim and infringes it.

The decision concludes as follows: "The search lights shed by defendants' exhibits upon the history of this art only serve to illumine the inventive conception of Tesla. The Arago rotation taught the schoolboy 50 years ago to make a plaything which embodied the principle that a "rotating field could be used to rotate an armature." Baily dreamed of the application of the Arago theory by means of a confessedly impossible construction. Deprez worked out a problem which involved the development of the general theory in providing an indicator for a ship's compass. Siemens failed to disclose the "suitable modifications" whereby his electric light machine might be transferred into a motor, and Bradley is almost equally vague. Eminent electricians united in the view that by reason of reversals of direction and rapidity of alterations an alternating current motor was impracticable, and the future belonged to the commutated continuous current. It remained to the genius of Tesla to capture the unruly, unrestrained and hitherto opposing elements in the field of nature and art and to harness them to draw the machines of man. It was he who first showed how to transform the toy of Arago into an engine of power; the "laboratory experiment" of Baily into a practically successful motor; the indicator into a driver; he first conceived the idea that the very impediments of reversal in direction, the contradictions of alternations might be transformed into power producing rotations, a whirling field of force. What others looked upon as only invincible barriers, impassable currents and contradictory forces, he seized, and by harmonizing their directions utilized in practical motors in distant cities the power of Niagara.

"A decree may be entered for an injunction and an accounting as to all the claims in suit."

Messrs. F. H. Betts, Kerr, Page & Cooper, and L. E. Curtis, on the brief, appeared for the complainant; and Mitchell, Bartlett & Brownell for the de- fendants.