mica Co., 266 U. S. 342, 349, is “that an assignor of a patent right is estopped to attack the utility, novelty or validity of a patented invention which he has assigned or granted as against any one claiming the right under his assignment or grant. As to the rest of the world, the patent may have no efficacy and create no right of monopoly; but the assignor can not be heard to question the right of his assignee to exclude him from its use. Curran v. Burdsall, 20 Fed. 835; Ball & Socket Fastener Co. v. Ball Glove Fastening Co., 58 Fed. 818; Woodward v. Boston Lasting Machine Co., 60 Fed. 283, 284; Babcock v. Clarkson, 63 Fed. 607; Noonan v. Chester Park Athletic Co., 99 Fed. 90, 91.”
Respondents, denying that the doctrine of estoppel can rightly be applied to patent assignments, also insist that the present case is not within the scope of the doctrine. Compare Buckingham Products Co. v. McAleer Mfg. Co., 108 F. 2d 192 with Casco Products Corp. v. Sinko Tool & Mfg. Co., 116 F. 2d 119. Both parties rely on the decision of this Court in the Formica case, supra, which, although stating that the assignor cannot deny the novelty and validity of the assigned patented invention, nevertheless held that the claims of a patent may be narrowed by reference to the prior art so as to restrict them to so much of the invention described by the specifications as is not exhibited by the prior art. Klein v. Russell, 19 Wall. 433, 466, 467; Garneau v. Dozier, 102 U. S. 230; Wollensak v. Reiher, 115 U. S. 87; Beidler v. United States, 253 U. S. 447; Mackay Co. v. Radio Corp., 306 U. S. 86, 94. Cf. Hocking & Co. v. Hocking, 4 R. P. C. 255, 434, 6 R. P. C. 69; Clark v. Adie, 2 App. Cas. 423; Crosthwaite v. Steel, 6 R. P. C. 190.
This Court in the Formica case, passing the question, not present here, whether the estoppel of the assignor extends to claims added by the assignee to the application in the Patent Office, held that the estoppel did not, in any