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Opinion of the Court.
The devices and arrangements specified are suitable for effecting the electrical transmission of signals in the manner already indicated. By the maintenance of the same high frequency throughout the four-circuit system the cumulative resonance is attained which gives the desired increased efficiency in transmission and increased selectivity at the receiving station.
The patent describes the operation of the four circuits as follows, beginning with the transmitter:
"In operation the signalling-key b is pressed, and this closes the primary of the induction-coil. Current then rushes through the transformer-circuit and the condenser e is charged and subsequently discharges through the spark-gap. If the capacity, the inductance, and the resistance of the circuit are of suitable values, the discharge is oscillatory, with the result that alternating currents of high frequency pass through the primary of the transformer and induce similar oscillations in the secondary, these oscillations being rapidly radiated in the form of electric waves by the elevated conductor (antenna).
"For the best results and in order to effect the selection of the station or stations whereat the transmitted oscillations are to be localized I include in the open secondary circuit of the transformer, and preferably between the radiator f and the secondary coil d', an inductance-coil g, Fig. 1, having numerous coils, and the connection is such that a greater or less number of turns of the coil can be put in use, the proper number being ascertained by experiment."
signalling device could pass. By means of a device which tapped the sides of the tube, the stream of filings was broken when the highfrequency oscillations ceased. Thus the coherer was a sensitive device by which weak, high-frequency signals could be made to actuate a low-frequency current of sufficient power to operate a telegraphic key or other device producing a visible or audible signal.
Opirion of the Court.
The invention thus described may summarily be stated to be a structure and arrangement of four high frequency circuits, with means of independently adjusting each so that all four may be brought into electrical resonance with one another. This is the broad invention covered by Claim 20. Combinations covering so much of the invention as is embodied in the transmitter and the receiver respectively are separately claimed.
Long before Marconi's application for this patent the scientific principles of which he made use were well understood and the particular appliances constituting elements in the apparatus combination which he claimed were well known. About seventy years ago Clerk Maxwell described the scientific theory of wireless communication through the transmission of electrical energy by ether waves. Between 1878 and 1890 Hertz devised apparatus for achieving that result which was described by de Tunzelmann in a series of articles published in the London
o Of the claims in suit in No. 369, Claims 10 and 20 cover the fourcircuit system, while Claims 1, 3, 6, 8, 11 and 12 cover the two transmitter circuits and Claims 2, 13, 14, 17, 18 and 19 cover the two receiver circuits. Claim 10 merely provides that the four circuits be in resonance with each other and hence does not prescribe means of adjusting the tuning. Claim 11 likewise prescribes no means of adjustment. The other claims provide means of adjustment, either a "variable inductance” (Claims 1, 2, 3, 8, 12, 13, 18, and 19) or more generally "means" for adjusting the period of the circuits (Claims 3, 6, 14 and 17). Some of the claims merely provide means of adjusting the tuning of the antenna circuit (Claims 1, 2, 8, 12, and 13) and hence do not require that the closed circuits be tuned. Others either specifically prescribe the adjustable tuning of both circuits at transmitter (Claims 3, 6) or receiver (Claims 18 and 19) or both (Claim 20) or else prescribe “means for adjusting the two transformer-circuits in electrical resonance with each other, substantially as described” (Claims 14 and 17).
G A Dynamical Theory of the Electromagnetic Field (1864), 155 Philosophical Transactions of the Royal Society 459; 1 Scientific Papers of James Clerk Maxwell 526.
Opinion of the Court.
Electrician in 1888. One, of September 21, 1888, showed a transmitter comprising a closed circuit inductively coupled with an open circuit. The closed circuit included a switch or circuit breaker capable of use for sending signals, and an automatic circuit breaker capable, when the switch was closed, of setting up an intermittent current in the closed circuit which in turn induced through a transformer an intermittent current of higher voltage in the open circuit. The open circuit included a spark gap across which a succession of sparks were caused to leap whenever the signal switch was closed, each spark producing a series of high frequency oscillations in the open circuit.
By connecting the spark gap to large area plates in the open circuit Hertz increased the capacity and thus not only increased the force of the sparks but also changed one of the two factors determining the frequency of the oscillations in the circuit, and hence the wave length of the oscillations transmitted. Hertz's receiver was shown as a rectangle of wire connected to the knobs of a spark gap, both the wire and the spark gap being of specified lengths of such relationship as to render the circuit resonant to the wave lengths in the transmitter. At times Hertz attached to the rectangle additional vertical wires which provided additional capacity, and whose length could readily be varied so as to vary the wave lengths to which the receiver was responsive, thus providing a "method of adjusting the capacity" of the receiver.? Thus Hertz at the outset of radio communication recognized the importance of resonance and provided means for securing it by tuning both his transmitting and re
See the London Electrician for September 21, 1888, p. 628. Ebert, in the London Electrician for July 6, 1894, p. 333, likewise pointed out that Hertz's receivers are "so arranged that they show the maximum resonant effect with a given exciter; they are 'electrically tuned.'”
ceiving circuits to the same frequency, by adjusting the capacity of each.s
Lodge, writing in the London Electrician in 1894, elaborated further on the discoveries of Hertz and on his own experiments along the same lines. In one article, of June 8, 1894, he discussed phenomena of resonance and made an observation which underlies several of the disclosures in Marconi's patent. Lodge pointed out that some circuits were by their nature persistent vibrators, i. e., were able to sustain for a long period oscillations set up in them, while others were so constructed that their oscillations were rapidly damped. He said that a receiver so constructed as to be rapidly damped would respond to waves of almost any frequency, while one that was a persistent vibrator would respond only to waves of its own natural periodicity. Lodge pointed out further that Hertz's transmitter “radiates very powerfully" but that "In consequence of its radiation of energy, its vibrations are rapidly damped, and it only gives some three or four good strong swings. Hence it follows that it has a wide range of excitation, i. e., it can excite sparks in conductors barely at all in tune with it.” On the other hand Hertz's receiver was "not a good absorber but a persistent vibrator, well adapted for picking up disturbances of precise
8 De Tunzelmann shows that Hertz clearly understood the principles of electrical resonance. Some of his early experiments were designed to determine whether principles of resonance were applicable to high frequency electrical circuits. From them Hertz concluded that "an oscillatory current of definite period would, other conditions being the same, exert a much greater inductive effect upon one of equal period than upon one differing even slightly from it.” Id. p. 626. Hertz knew that the frequency to which a circuit was resonant was a function of the square root of the product of the self-inductance and capacity in the circuit and by a formula similar to that now used he calculated the approximate frequency of the oscillations produced by his transmitter. Id., September 28, 1888, 664-5.
Opinion of the Court.
and measurable wave-length.” Lodge concluded that "The two conditions, conspicuous energy of radiation and persistent vibration electrically produced, are at present incompatible.” (pp. 154–5.)
In 1892, Crookes published an article in the Fortnightly Review in which he definitely suggested the use of Hertzian waves for wireless telegraphy and pointed out that the method of achieving that result was to be found in the use and improvement of then known means of generating electrical waves of any desired wave length, to be transmitted through the ether to a receiver, both sending and receiving instruments being attuned to a definite wave length. A year later Tesla, who was then preoccupied with the wireless transmission of power for use in lighting or for the operation of dynamos, proposed, in a lecture before the Franklin Institute in Philadelphia, the use of adjustable high frequency oscillations for wireless transmission of signals.10
Marconi's original patent No. 586,193, which was granted July 13, 1897, and became reissue No. 11,913, disclosed a two-circuit system for the transmission and reception of Hertzian waves. The transmitter comprised an antenna circuit connected at one end to an aerial plate and at the other to the ground, and containing a spark gap. To the knobs of the spark gap was connected a transformer whose secondary was connected with a source of current and a signalling key. The low frequency current thereby induced in the antenna circuit was caused to discharge through the spark gap, producing the high frequency oscillations which were radiated by the antenna. The receiver similiarly contained an antenna circuit between an elevated plate and the ground, in which
Fortnightly Review, No. 101, February, 1892, 173, 174–5. 10 Martin, Inventions, Researches and Writings of Nikola Tesla, pp. 346-8.