1 Opinion of the Court. vary the capacity by being slid upon each other." Marconi, however, makes no claim for the particular construction of the condenser. Although the claim broadly provides for "means of adjusting the two transformer-circuits in electrical resonance," Marconi's drawings disclose the use of a variable inductance connected between the aerial conductor and the transformer-coil in such a manner that the variable inductance is not included in that part of the antenna circuit which is bridged by the condenser. The condenser is thus arranged in parallel with the transformer coil and in series with the variable inductance. In his specifications Marconi enumerates a number of preferred adjustments for tuning the transmitting and receiving stations, showing the precise equipment to be used to achieve tuning to the desired wave-length. The two tunings which show the use of the adjustable condenser in the receiver antenna also make use of the variable inductance. And his specifications state: "In a shunt around said primary j [the primary of the transformer] I usually place a condenser h ... An inductance coil g1 of variable inductance is interposed in the primary circuit of the transformer, being preferably located between the cylinder f1 [the aerial capacity] and the coil j1." In this respect the devices which the court below found to infringe Claim 16 exhibit somewhat different arrangements. Apparatus manufactured by the Kilbourne and Clark Company, and used by the Government, had a receiver antenna circuit containing a variable inductance in addition to the transformer coil, and having an adjustable condenser so constructed that it could be connected either in series with the two inductances, or in a shunt bridging both of them. Apparatus manufactured by the Telefunken Company showed a similar antenna circuit having no variable inductance, but having an adjustable condenser so arranged that it could be connected either in Opinion of the Court. 320 U.S. series with the transformer coil, or in parallel with it by placing the condenser in a shunt circuit which would thus bridge all the inductance in the antenna circuit. The Marconi patent does not disclose the function which is served by the adjustable condenser disclosed by Claim 16, except in so far as Marconi in his specifications, in describing the means of tuning the receiver circuits to a particular desired frequency, prescribes specific values for both the variable inductance and the adjustable condenser in the receiver antenna circuit. The Court of Claims found that this indicated "that the purpose of the condenser connected in shunt with the primary winding of the transformer of the receiver, is to enable the electrical periodicity or tuning of the open circuit of the receiver to be altered." The court thus based its holding that Claim 16 disclosed patentable invention on its finding that Marconi, by the use of an adjustable condenser in the antenna circuit, disclosed a new and useful method of tuning that circuit. The Government contends that the arrangement of the antenna circuit disclosed by Marconi's specifications— with the condenser shunted around the transformer coil but not around the variable inductance-is such that the condenser cannot increase the wave-length over what it would be without such a condenser, and that it can decrease that wave-length only when adjusted to have a very small capacity. The Government contends therefore that its principal function is not that of tuning but of providing "loose coupling." 22 The Government does not deny that this precise arrangement is novel and useful, but it contends that its devices do not infringe that 22 See note 13, supra. Most of the current in the antenna circuit is said to pass through the condenser shunt and not through the transformer coil, thus minimizing the effect upon the frequency of vibrations in the antenna circuit of the magnetic stresses set up in the primary of the transformer by the current induced in the secondary. 1 Opinion of the Court. precise arrangement, and that Claim 16, if more broadly construed so as to cover its apparatus, is invalid because anticipated by the prior art, particularly the patents of Pupin and Fessenden. As we have seen from our discussion of the other claims of the Marconi patent, the idea of tuning the antenna circuits involved no patentable invention. It was well known that tuning was achieved by the proper adjustment of either the inductance or the capacity in a circuit, or both. Lodge and Stone had achieved tuning by the use of an adjustable induction coil, so arranged that its effective inductance could readily be varied. But capacity was no less important in tuning. De Tunzelmann's descriptions of Hertz's experiments show that Hertz, in order to make his receiving apparatus resonant to the particular frequency radiated by the transmitter, carefully determined the capacity of both, and indeed disclosed a means of adjusting the capacity of the receiver by attaching to it wires whose length could readily be varied. Marconi in his prior patent No. 586,193, granted July 13, 1897, which became reissue No. 11,913, had disclosed a two-circuit system for the transmission of radio waves in which both transmitter and receiver had large metal plates serving as capacity areas. His specifications describe the construction of transmitting and receiving stations so as to be resonant to the same frequency by calculation of the length of these metal plates, thereby determining the capacity of the antenna circuits of transmitter and receiver respectively. He states that the plates are “preferably of such a length as to be electrically tuned with the electric oscillations transmitted," and describes means of achieving this result so as to determine "the length most appropriate to the length of wave emitted by the oscillator." Claim 24 of his patent claims "the combination of a transmitter capable of producing electrical oscillations or rays of definite character at the Opinion of the Court. 320 U.S. will of the operator, and a receiver located at a distance and having a conductor tuned to respond to such oscillations .. The only means of achieving this tuning disclosed by the specifications is the determination of the capacity of the antenna of transmitter and receiver in the manner described. Moreover the use of an adjustable condenser as a means of tuning was known to the prior art. Pupin in patent No. 640,516, applied for May 28, 1895, and granted January 2, 1900, before Marconi, disclosed the use of an adjustable condenser as a means of tuning a receiving circuit in a system of wired telegraphy. Pupin's patent was designed to permit the simultaneous transmission over a wire of several messages at different frequencies, and the selective reception at a given receiving station of the particular message desired, by tuning the receiving circuit to the frequency at which that message was transmitted. His specifications and drawings disclose at the receiver a telegraph key or other suitable detecting instrument located in a shunt from the wire along which the messages were passed. The shunt circuit included a condenser "of adjustable capacity," an adjustable induction coil, and a detecting instrument. His specifications state that "the capacity of the condenser H and the self-induction of the [induction] coil I being such that the natural period or frequency of the shunt or resonance circuit HI is the same as the period of one of the electromotive forces which produce the current coming over the line. . . this circuit HI will be in resonance with the current and therefore will act selectively with respect to it." He disclosed an alternative system in which a similar shunt circuit containing a condenser, already described as of adjustable capacity, and the primary of a transformer, was inductively coupled with another circuit containing the secondary of the transformer, an induction coil, an adjustable condenser, and a receiving device. He thus in effect dis 1 Opinion of the Court. closed an open receiving circuit with earth connection including the primary of an oscillation transformer-the secondary of which is connected in a circuit with a telegraph key or other suitable detecting instrument—and an adjustable condenser in a shunt bridging the primary of the transformer and thus connected in parallel with it. Thus Pupin showed the use of an adjustable condenser as a means of tuning an electrical circuit so as to be selectively receptive to impulses of a particular frequency. It is true that his patent related not to the radio art but to the art of wired telegraphy, an art which employed much lower frequencies. But so far as we are informed the principles of resonance, and the methods of achieving it, applicable to the low frequencies used by Pupin are the same as those applicable to high frequency radio transmission and reception. Fessenden, in patent No. 706,735, applied for Dec. 15, 1899, before Marconi, and granted Aug. 12, 1902, disclosed, in the antenna circuit of a radio receiver, a condenser in a shunt around a coil. The coil was used in effect as a transformer; by the magnetic lines of force set up when a current passed through it an indicator was caused to move, thereby either closing an electrical connection or giving a visible signal. Fessenden's specifications do not clearly disclose the purpose of his condenser, but they specify that it must be "of the proper size." He also discloses a condenser in a shunt circuit around the terminals of a spark gap in the antenna circuit of the transmitter, and his specifications prescribe that "This shunt-circuit must be tuned to the receiving-conductor; otherwise the oscillations produced by it will have no action upon the wave-responsive device at the receiving-station." We have referred to the Pupin and Fessenden patents, not for the purpose of determining whether they anticipate Claim 16 of Marconi, as the Government insists, but to indicate the importance of considering them in that |