This case is briefed and argued here as though it were a nisi prim proceeding. While this practice is not limited to patent cases, it appears most prevalent in this field of litigation. We are thus prompted to make some observations relative to our function as a reviewing court. In doing so, we think it apparent that there has been a tendency to place the review of patent cases in a category different from other cases. This tendency, we suspect, has developed in large part from the uncertainty and confusion heretofore existing as to whether the answer to the question of patentable invention or infringement is to be characterized as a Finding of Fact or a Conclusion of Law. Obviously, if the answer is treated as a Finding of Fact, it comes within Rule 52(a) and is.binding upon this court “unless clearly erroneous.” This confusion and uncertainty as to what constitutes a Finding of Fact in a patent case has been laid to rest by the Supreme Court in Graver Tank & Mfg. Co., Inc. et al. v. Linde Air Products Co., 336 U.S. 271, 69 S.Ct. 535, 93 L.Ed. 672. (See also the decision in the same case on rehearing, 70 S.Ct. 854.) There, the court, concerning the findings that certain claims were valid, 336 U.S. on page 275, 69 S.Ct. at page 537, 93 L.Ed. 672 stated: “The rule [52(a) ] requires that an appellate court make allowance for the advantages possessed by the trial court in appraising the significance of conflicting testimony and reverse only ‘clearly erroneous’ findings”, and concluded that the findings “are manifestly supported by substantial evidence.” And as to the findings of the trial court that certain of the claims were invalid, the Supreme Court stated 336 U.S. at page 279, 69 S.Ct. at page 539, 93 L.Ed. 672: “The same deference is due to the findings of the trial court which overturn claims as to those which sustain them. * But the record in this case, while not establishing to a certainty that the findings are right, fall far short of convincing us that they are clearly erroneous.”
A rehearing was allowed in the case under discussion upon the question of infringement of the claims the validity of which the court had previously sustained. Related to the issue of infringement was the applicability of the doctrine of equivalence. In a decision rendered May 29, 1950, 70 S.Ct. 854, 857, the court stated (page 4, slip opinion) : “A finding of equivalence is a determination of fact. Proof can be made in any form: through testimony of experts or others versed in the technology; by documents, including texts and treatises; and, of course, by the disclosures of the prior art. Like any other issue of fact, final determination requires a balancing of credibility, persuasiveness and weight of evidence. It is to be decided by the trial court and that court’s decision, under general principles of appellate review, should not be disturbed unless clearly erroneous.”
Thus, there is no room longer to doubt that the issues most prevalent in patent litigation, and particularly those of validity or invalidity, infringement or non-infringement, are issues of fact and that a finding by the trial court on such issues is within the terms of Rule 52(a), which a court of review is not at liberty to set aside unless “clearly erroneous.” Thus, factual issues in a patent case must be tried and decided by the trial judge in precisely the same manner as those in any other kind of a law suit, and the function of this court on review is no different than that in any other kind of a case.
Turning now to the contested issues, we shall first consider Admiral’s charge that there has been such a misuse of patents by Hazeltine as to bar the enforcement of the patent in suit against Admiral. There are two provisions of Hazeltine’s lice.nse agreements principally relied upon in this respect, namely, (1) the exaction of royalty on entirely unpatented products made by plaintiff’s licensees, and (2) the requirement that each licensee mark all his products, whether patented or unpatented, with a notice restricting the uses to which a purchaser may put those products.
This misuse issue, predicated upon the same grounds asserted here, was made against Hazeltine and decided in its favor by the First Circuit. Automatic Radio Mfg. Co., Inc. v. Hazeltine Research, Inc., 176 F.2d 799. Certiorari was allowed by the