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Opinion of the Court.

frequency oscillations in a circuit, and to determine their frequency by proper distribution of capacity and selfinductance in the circuit, but also to transfer those oscillations to another circuit and retain their original frequency.

Stone points out that in the existing systems of radio transmission the electric oscillations are "naturally" developed in the antenna circuit by the sudden discharge of accumulated electrical force through a spark gap in that circuit. Such oscillations are "necessarily of a complex character and consist of a great variety of superimposed simple harmonic vibrations of different frequencies." "Similarly the vertical conductor at the receiving station is capable of receiving and responding to vibrations of a great variety of frequencies so that the electro-magnetic waves which emanate from one vertical conductor used as a transmitter are capable of exciting vibrations in any other vertical wire as a receiver . . . and the messages from the transmitting station will not be selectively received by the particular receiving station with which it is desirous to communicate, and will interfere with the operation of other receiving stations within its sphere of influence."

In contrast to the two-circuit system whose inadequacies he had thus described, Stone's drawings and specifications disclose a four-circuit system for transmitting and receiving radio waves which was very similar to that later disclosed by Marconi. The transmitter included a source of low frequency oscillating current and a telegraph or signalling key connected in a circuit which was inductively coupled with another closed circuit. This included an induction coil, a condenser, and a spark gap capable of generating high frequency oscillations. It in turn was inductively coupled through a transformer with an open antenna circuit connected to an aerial capacity at one end and the earth at the other. The receiver included a sim

Opinion of the Court.

320 U.S.

ilar antenna circuit, inductively coupled with a closed oscillating circuit containing an induction coil, a condenser, and a coherer or other detector of radio waves.

Stone thus recognized, although he used different terminology, the fact, previously observed by Lodge, that an open antenna circuit, so constructed as to be an efficient radiator, was not an oscillator capable of producing natural waves of a single well-defined periodicity, and consequently had a wide range of excitation. He adopted the same remedy for this defect as Marconi later did, namely to produce the oscillations in a closed circuit capable of generating persistent vibrations of well-defined periodicity, and then induce those oscillations in an open antenna circuit capable of radiating them efficiently to a distant resonant receiver. He states that the vibrations in his closed circuit "begin with a maximum of amplitude and gradually die away," a good description of the results obtainable by a "persistent oscillator." 13 Similarly in his receiver Stone recognized that an open antenna circuit (Lodge's "good absorber") was not a highly sensitive responder to waves of a particular frequency, and accordingly he sought to augment the selectivity of tuning at the receiver by interposing between the antenna circuit and the responding device a closed circuit which would be a more persistent vibrator and hence render the receiv

13 That the closed circuit was intended to be a "persistent oscillator" is also brought out by Stone's emphasis on "loose coupling." Stone's application explained in detail the fact that when two circuits are inductively coupled together there normally result "two degrees of freedom," that is to say, the superposition of two frequencies in the same circuit because of the effect on each of the magnetic lines of force set up by the other. He discussed in detail methods of eliminating this superposition, which interfered with accurate selectivity of tuning, by so constructing his circuits as to be "loosely coupled." This he achieved by including in the closed circuits a large inductance coil, which had the effect of "swamping" the undesirable effect of

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Opinion of the Court.

ing apparatus more selectively responsive to waves of a particular frequency. In so doing, however, as will presently appear, he did not disregard the favorable effect on selectivity of tuning afforded by making the antenna circuits resonant to the transmitted frequency.

Stone's application recommends that the inductance coils in the closed circuits at transmitter and receiver "be made adjustable and serve as a means whereby the operators may adjust the apparatus to the particular frequency which it is intended to employ." He thus disclosed a means of adjusting the tuning of the closed circuits by variable inductance. His original application nowhere states in so many words that the antenna circuits should be tuned, nor do its specifications or drawings explicitly disclose any means for adjusting the tuning of those circuits. But there is nothing in them to suggest that Stone did not intend to have the antenna circuits tuned, and we think that the principles which he recognized in his application, the purpose which he sought to achieve, and certain passages in his specifications, show that he recognized, as they plainly suggest to those skilled in the art, the desirability of tuning the antenna circuits as well. The disclosures of his application were thus an adequate basis for the specific recommendation, later added by amendment, as to the desirability of constructing the

the lines of force set up in the primary of the transformer by the current induced in the secondary. Since the turns of wire in the primary of the transformer constituted a relatively small part of the total inductance in the closed circuit the effect of those turns on the frequency of the circuit was minimized.

But the testimony at the trial was in substantial agreement that the looser the coupling the slower is the transfer of energy from the closed charging circuit to the open antenna circuit. Hence the use of loose coupling presupposes a charging circuit that will store its energy for a considerable period, i. e., that will maintain persistent oscillations.

Opinion of the Court.

320 U.S.

antenna circuits so as to be resonant to the frequency produced in the charging circuit of the transmitter.

The major purpose of Stone's system was the achievement of greater selectivity of tuning. His objective was to transmit waves "of but a single frequency" and to receive them at a station which "shall be operated only by electric waves of a single frequency and no others." He states:

"By my invention the vertical conductor of the transmitting station is made the source of electro-magnetic waves of but a single periodicity, and the translating apparatus at the receiving station is caused to be selectively responsive to waves of but a single periodicity so that the transmitting apparatus corresponds to a tuning fork sending but a single simple musical tone, and the receiving appaiatus corresponds to an acoustic resonator capable of absorbing the energy of that single, simple musical tone only."

He says that "when the apparatus at a particular [receiving] station" is properly tuned to a particular transmitting station the receiver will selectively receive messages from it. He adds:

"Moreover, by my invention the operator at the transmitting or receiving station may at will adjust the apparatus at his command in such a way as to place himself in communication with any one of a number of stations ... by bringing his apparatus into resonance with the periodicity employed."

And with respect to the transmitter he says, "It is to be understood that any suitable device may be employed to develop the simple harmonic force impressed upon the vertical wire [antenna]. It is sufficient to develop in the vertical wire practically simple harmonic vibrations of a fixed and high frequency."

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Opinion of the Court.

These statements sufficiently indicate Stone's broad purpose of providing a high degree of tuning at sending and receiving stations. In seeking to achieve that end he not unnaturally placed emphasis on the tuning of the closed circuits, the association of which with the antenna circuits was an important improvement which he was the first to make. But he also made it plain that it was the sending and receiving "apparatus" which he wished to tune, so that the sending "apparatus" "would correspond to a tuning fork" and the receiving "apparatus" to "an acoustic resonator" capable of absorbing the energy of the "single, simple musical tone" transmitted. And this he sought to achieve by "any suitable device."

Stone thus emphasized the desirability of making the entire transmitting and receiving "apparatus" resonant to a particular frequency. As none of the circuits are resonant to a desired frequency unless they are tuned to that frequency, this reference to the transmitting and receiving apparatus as being brought into resonance with each other cannot fairly be said to mean that only some of the circuits at the transmitter and receiver were to be tuned. To say that by this reference to the tuning of sending and receiving apparatus he meant to confine his invention to the tuning of some only of the circuits in that apparatus is to read into his specifications a restriction which is plainly not there and which contradicts everything they say about the desirability of resonance of the apparatus. It is to read the specifications, which taken in their entirety are merely descriptive or illustrative of his invention, compare Continental Paper Bag Co. v. Eastern Paper Bag Co., 210 U. S. 405, 418, 419-20, as though they were claims whose function is to exclude from the patent all that is not specifically claimed. Mahn v. Harwood, 112 U. S. 354, 361; McClain v. Ortmayer, 141 U. S. 419, 423-5; Milcor Steel Co. v. Fuller Co., 316 U. S. 143, 146.