Appeal from the decree of the District Court, dismissing the bill brought by the plaintiff under section 4918 of the Revised Statutes (Comp. St. § 9463), seeking to have Vreeland patent, No. 1,239,852, granted September 11, 1917, for receiver for electrical impulses, and Vreeland patent, No. 1,245,166, granted November 6,1917, for method of transmitting and receiving high-frequency impulses, adjudged void, as interfering with Fessenden patent, No. 1,050,441, granted January 14, 1913, for electrical signaling apparatus, and Fessenden patent, No. 1,050,728, granted January 14, 1913, for method of signaling. Plaintiff’s specific contention is that the court should annul claims 1 to 8, inclusive, of Vreeland patent, No. 1,239,852, as interfering with claims 3, 4, and 29 of Fessenden patent, No. 1,050,-441, and that, such interference having been established, the court may and should hold claims 9 to 28 of the Vreeland patent invalid, in view of the disclosure of Fessenden and the then state of the art (General Chemical Co. v. Blackmore (C. C.) 156 Fed. 968; but see Boston Pneumatic Tire Co. v. Eureka Patents Co. [C. C.] 139 Fed. 29); further, that all the claims of Vreeland patent, No. 1,245,166, should be annulled, as interfering with claims 10, 11, 12, 13, and 14 of Fessenden patent, No. 1,050,728. _
_ The patents in question relate to the art of radio telegraphy and telephony. All of them involve wireless systems which utilize continuous or substantially continuous waves; that is, the so-called undamped waves, as distinguished from the damped waves of the old “spark” system. The damped waves are formed in groups or trains of relatively short duration, with long intervals of inactivity between groups, the waves or oscillations of each group being “damped”; that is, of rapidly decreasing amplitude or strength. An undamped wave is persistently generated and is of constant amplitude. All of the patents make use of the “heterodyne” principle, involving the production of signals by means of harmonic beats, analogous to musical beats. These are produced by the co-operation of the currents of the received electrical pulses and the locally produced forces. The heterodyne principle makes it possible to overcome many atmospheric disturbances, and to select the signals from a given station to the substantial exclusion of signals from other stations. The beats produced are measured by the difference between the frequency of the received wave and of the locally generated oscillations. The receiver controls the pitch of the signal note by controlling the frequency of the oscillations. The utilization of the continuous undamped waves and the beats principle marked a very great advance in the art. Kintner et al. v. Atlantic Communication Co. (D. C.) 249 Fed. 73.
[1] The Fessenden inventions, covered by the patents in suit, are admittedly prior in time. His claims, alleged to be interfered with, are broad in scope; if valid (and validity is not here contested), the utilization of Vreeland’s patent concededly would involve infringement *470thereof. But the question raised by this bill is that of interference under R. S. § 4918, not that of infringement; that is, it is not whether the plaintiff could enjoin the use of the method and product of the Vreeland patents, but whether there is substantial identity of scope, though not necessarily literal identity of language, in certain claims of the Fessenden and Vreeland patents. While, to ascertain the invention covered by a claim, the claim is to be interpreted in the light, not only of text, but of the specifications and drawings, and of the prior art, substantial identity in whole or in part in the invention so claimed must be found as a prerequisite to interference. Stonemetz Co. v. Brown Co. (C. C.) 57 Fed. 601; Nathan v. Craig (C. C.) 49 Fed. 370; Simplex Ry. Appliance Co. v. Wands, 115 Fed. 517, 53 C. C. A. 171.
[2] Two patents should not be issued for the same invention; if the Patent Examiner believes that such identity exists, either between two pending applications or between a pending application and a patent, verbally identical claims áre suggested, and an interference declared by the Patent Office to determine priority of invention. If', however, two such patents have issued, the court, not the Patent Office, is the forum; proceedings under section 4918 may be brought. The aim, however, is unchanged; to determine priority of invention, and, on the basis thereof, to annul the patent erroneously and/or inadvertently issued. The court will not, however, engage in a useless investigation of priority; if there is no patentable invention, the bill will be dismissed. Palmer Pneumatic Tire Co. v. Lozier, 90 Fed. 733, 33 C. C. A. 255; Simplex Ry. Appliance Co. v. Wands, supra.
In a limited sense, so far as establishing inter partes the question of priority of invention, interference proceedings partake of the nature of the so-called declaratory judgments, a subject-matter of very recent legislation. See Borchard, The "Uniform Act on Declaratory Judgments, 34 Harvard L. R. 697. Clearly, however, section 4918 does not provide for a declaratory decree to establish even inter partes the validity or scope of the claims either of a basic patent or of a concededly junior improvement patent; actual or threatened infringement is essential for a suit to settle these questions.
[3] If, then, the concededly junior patentee is claiming an alleged specific improvement of the prior and basic patent, the patentability of the alleged improvement is not the subject-matter of an interference suit. Stonemetz Co. v. Brown Co., supra; Boston Pneumatic Power Co. v. Eureka Patents Co., supra.
[4] Applications for the patents here in controversy were pending in the Patent Office at the same time. Five of Vreeland’s claims in his transmitter application were suggested to and accepted by Fessen-den, and, in the contested interference that was declared by the Patent Office, Fessenden’s right thereto was sustained. It is quite possible, as the file wrappers appear to indicate, that other claims in the Vreeland patents, as originally framed in ignorance of Fessenden’s prior application, either covered the same invention or presented no patentable advance thereover. The Examiners endeavored to allow only those claims which, in their judgment, indicate some step forward in the art. Vree-land thought that the full scope of his invention was not recognized, and pressed, but without success, an appeal on some of his claims.
*471While the courts are not bound by the decision of the Patent Office as to the validity of those claims which were finally allowed, the considered decision o£ the Patent Office is entitled to great weight, and, in view of the careful examination of Vreeland’s claims by the Patent Office, and its conscious endeavor to eliminate those in interference with or not patentable over Fessenden, only the clearest conviction of identity of claims would justify the court now to find an interference. The Patent Office would not have allowed the claims in question, in the light of its own comparison with the Fessenden claims, unless it considered that they not otily asserted, but actually embodied, a patentable advance over Fessenden’s claimed inventions. As Chief Justice Taft says in Hildreth v. Mastoras (U. S. Supreme Court, November 7, 1921), 257 U. S. —, 42 Sup. Ct. 20, 66 L. Ed. —:
“The presumption of priority and novelty [and, we may add here, noninterference]'which arises from the granting of a patent must have greatly increased weight, and the claim of the inventor is subjected to such close and careful scrutiny under the stimulus of a heated contest.”
Whether or not the asserted improvement embodies a patentable advance may be contested and determined in an infringement suit; indeed, defendant has sued plaintiff for an alleged infringement of these very claims. This court, however, would not be justified on this record in holding that Vreeland clearly did not even assert a patentable improvement over Fessenden. Fet us consider the receiver or apparatus patents (Fessenden patent, No. 1,050,441, and Vreeland patent, No. 1,-239,852) first:
Claim 3 of Fessenden may be compared with claim 1 of Vreeland as typical of the interference claimed. Fessenden’s claim 3 reads:
“A signal system having in combination at a receiving station, a receiver and a constantly operating frequency determining element having a frequency differing from that of the received impulses to such an extent as to cause beats to be formed at the station on the receipt of transmitted pulses.” .
Vreeland’s claim 1 states:
“A receiver of sustained high-frequency signal impulses, wherein are combined a detector, a local source of sustained alternating currents of slightly different frequency from the signal impulses, and means for combining the local currents with the signal impulses, and applying the resultant heat current to the detector, substantially as set forth.”
Vreeland’s contention is that, while his claim may infringe Fessen-den’s patent, it goes beyond it and makes a substantial contribution to the art, in suggesting, not merely the mechanical interaction of the received and locally generated current to produce beats, but the combination of the two currents to form a resultant beat current, which is applied as a unit to the detector. Although the use of such a resultant beat current may fall foul of Fessenden’s generic claims in an infringement suit, such a resultant beat current cannot be said to be so described or referred to in Fessenden’s claim as to involve Vreeland’s claims in interference.
Vreeland contends that there is no inkling in Fessenden’s patent of the combining of the received current and locally generated current in. a common circuit, so as to prpduce a new resultant beat current. He *472points out that Fessenden uses a dynamometer telephone with two separate coils. Plaintiff contends, however, that by induction the currents in the two separate coils of Fessenden’s dynamometer telephone combine in a common circuit and produce a resultant current. Vree-land denies that such a resultant current is a regular or necessary incident of Fessenden’s patent, and states that any such, current developed would be inefficient and not dependable and consequently could not be regarded as an anticipation of the resultant current described in his patent; and, of course, if necessary to sustain their validity, Vreeland’s claims may be limited by the descriptions contained in his specifications.
But plaintiff proceeds to point out that Fessenden specifies that his patent may be operated by an interaction of either electrostatic or magnetic fields, and that the reference to electrostatic fields would inevitably suggest to any one versed in the art the use of a condenser telephone, which is one of the favored devices of Vreeland for uniting the received and local .currents in a common circuit to produce a new beat current. Vreeland, however, takes the position that the use of the cqndenser telephone in this connection marked a distinct advance in the art over the preferred contrivances described by Fessenden, and that the means of utilizing the condenser telephone was not pointed out, or even understood, by Fessenden, who apparently deemed it desirable that the received and local currents be left in separate circuits.' Vree-land contends that this reference to electrostatic fields has no clear or definite content, and that it may have referred to a quadrant electrom-eter, a laboratory instrument used for measuring potential or electrical charges.
These considerations evidence that there is at least a substantial controversy between the parties as to whether the invention which Vree-land asserts he has made is a patentable advance over Fessenden’s disclosure. This may and should be determined in an infringement suit; but in view of the difference in the claims and the considered action of the Patent Office in respect thereto, an interference suit will not be allowed.
As to the transmitter or method patents, Vreeland maintains that his claims 1, 2, and 3 are distinguishable from and patentable over Fessen-den, by reason of their describing as the very essence of the invention, the combination of the current oscillations in the receiver “in a common element in a tuned circuit.” The issues thus raised are substantially the same as those discussed in connection with the receiver patents, and are not, in our judgment, appropriate for decision in an interference suit, under section 4918.
The interference issue raised, as between Vreeland’s transmitter claims 4 to 10 and Fessenden’s transmitter claims 10, 11, 12, 13, and 14, is somewhat different. It may be illustrated by a comparison of Fessenden’s claim 11 with Vreeland’s claim 8. Fessenden’s claim 11 reads:'
“The method of transmitting and receiving sustained alternating signal impulses, which consists in transmitting' a continuous wave train of sustained oscillations, changing the frequency of such continuous wave train to produce signals, combining with such transmitted wave train at the receiver locally generated sustained oscillations and observing the combined effects of such oscillations.”
*473Vreeland’s claim 8 is word for word the same as Fessenden’s claim 11 above cited, except for the addition of the word “abruptly” before .the clause “changing the frequency of such continuous wave train.” The identity of language, but for this one word, is due to the fact that it was Vreeland’s language; Vreeland, not Fessenden, was its author; Fessenden adopted it at the suggestion of the Patent Office on the interference issue, in which he was successful. With this record before it, the Patent Office subsequently allowed Vreeland’s claim with the addition noted, evidently for the reason that it considered the amended claim, read in light of Vreeland’s specifications, not only substantially different from, but a patentable advance over, Fessenden. Both patents involve the variation in pitch of the beat notes through a slight change in the frequency of the signal pulses. But Vreeland claims his invention m the abruptness with which he is able to effect this change by varying the electric constants of the system, and through which he contends increased clarity of audition and sharpness in beat note changes are achieved.
The abrupt character of the frequency changes is not specifically claimed by Fessenden. Plaintiff contends that Fessenden makes his changes abrupt enough for practical purposes, but that would not in itself necessarily invalidate a patent intended to secure abrupt note changes, with increased effectiveness. Plaintiff further maintains that Fessenden did not restrict himself to effective frequency changes, by varying the speed of the mechanical alternator shown in his drawings, but expressly referred to the use of a mercury lamp, and to his patent, No. 706,742, both of which, it contends, should suggest to one versed in the art the variation of wave frequency by a change in the constants of the circuit. Vreeland denies the sufficiency of these references; he points out that patent No. 706,742 relates to “spark signals,” and he maintains that it is in no event the simple equivalent of his contrivance. But the issues raised by these conflicting contentions go, not to the question of interference, but to that of patentable advance; that is, whether or not Vreeland is anticipated by the disclosures of Fessenden and by the prior art.
The trial judge was experienced in the trial of patent cases in this specific art; he heard the entire testimony, and took an active part in the examination of the witnesses; he has stated in his opinion that he was strongly impressed by Vreeland’s testimony. These circumstances and the Patent Office proceedings fortify us in our own conclusions that the decree must be affirmed.