plaintiff which constitute such conduct is, of course, impossible. An estoppel is pre-eminently the creature of circumstances, and only in the light of all those which enter into and surround the given transaction can its character be definitely known. Many of the actions of the plaintiff which might be relied on as resulting in an estoppel have also been regarded by the courts as creating an implied license to practise the invention, and such acts may be taken advantage of either under this or that form of defence. Among the omis

sions of the plaintiff, one derives its character and effect from the express provisions of the law. This consists in the neglect of the owner of the patent for an article to give the public information that the same is patented by stamping the article itself, or the package in which it is contained, with the word "patented," accompanied by the date of the patent. A plaintiff, who omits this duty, is estopped from claiming substantial damages for any infringement committed by the defendant before he receives notice from the plaintiff that his acts are an invasion of the patent. An omission to commence legal proceedings against infringers, within a reasonable time after their infringements became known to the owner of the patent, may work an estoppel in a court of equity.9 Whether it has the same effect in a court of law may well be doubted, except in cases where it is sufficient evidence of an abandonment of the invention to the public.10 But the institution of a single suit against one infringer is notice to all others that the plaintiff intends to vindicate his rights under the patent, and no delay in suing them can then raise an estoppel in their favor." The relation that subsists between

his invention is the same as that covered by his foreign patents, see Commercial Mfg. Co. v. Fairbank Canning Co. (1886), 27 Fed. Rep. 78; 36 O. G. 1473.

7 For a discussion of license by estoppel, see § 834 and notes, ante.

8 For the effect of a failure to stamp patented articles as required by law, see § 628 and notes, ante.

That a mere delay in suing an infringer may work an estoppel in equity,

see §§ 1114, 1194, 1195, and notes, post.

10 That in the absence of a Statute of Limitations a delay in suing an infringer does not work an estoppel, unless the conduct of the patentee is equivalent to an abandonment of the invention to the public, see Ransom v. Mayor of New York (1856), 1 Fisher, 252.

11 That the bringing a suit against one infringer is, in equity, notice to all

a transferor or transferee of any interest in a patented invention is also ground for an estoppel in a court of law, in any case where the transferor is plaintiff, and in his suit he must attack either the existence or validity of the transfer he has made,12

§ 982. Twenty-Fourth Defence: Release.

The twenty-fourth defence consists in an averment that the cause of action formerly existing in favor of the plaintiff against the defendant has been voluntarily extinguished by the plaintiff. A cause of action arising from the infringement of a patent may be destroyed by the owner of the patent in either of two methods: (1) By a surrender of the patent to the government, which terminates alike the existence of the patent and all rights of action based thereon; or, (2) By a release to the infringer, which terminates the cause of action but does not affect the existence of the patent. As the present defence does not attack the validity or existence of the patent, but the cause of action only, it is proper in the single case where the owner of the patent, subsequently to the infringement, has expressly or impliedly released the infringer from his liability therefor.1 Such a release may be in writing under seal, or may arise by presumption of law out of other transactions between the parties. The releasor must have had the legal right to grant it, and the defendant must have received it in good faith

others of their liability, and prevents an estoppel by laches, see § 1114 and notes, post.

12 That a transferor is estopped to deny the validity of the patent or the rights of his transferee, see Birdsall v. Curran (1887), 31 Fed. Rep. 918; 42 O. G. 1167; American Paper Barrel Co. v. Laraway (1886), 28 Fed. Rep. 141; 37 O.G. 674; Alabastine Co. v. Payne(1886), 27 Fed. Rep. 559; 35 O. G. 1438; Parker v. McKee (1885), 32 O. G. 137; 24 Fed. Rep. 808; Underwood v. Warren (1884), 21 Fed. Rep. 573; Thomas v. Quintard (1855), 5 Duer, 80; and §§ 787, 789, and notes, ante.

That a plaintiff cannot deny the ex

istence of a corporation through which he derived title, see Bogart v. Hinds (1885), 33 O. G. 1268; 25 Fed. Rep. 484.

§ 982. 1 That a release is a good defence to an action for infringement, see Goodyear v. McBurney (1853), 3 Blatch. 32.

That a written release under seal of one of two joint infringers is a bar to a suit against the other, though he may still be enjoined from further infringements, see Babcock & Wilcox Co. v. Pioneer Iron Works (1888), 43 O. G. 756.

2 That a release may be implied from circumstances, see 2 Pars. Cont. 715.

and not in fraud of other owners of the patented invention; and if it were conditional, such conditions must have been fulfilled. A plaintiff having given a valid release to the defendant is bound by it, not only as a contract relinquishing his former cause of action, but as an estoppel which prevents him from pursuing any remedy thereon.*

§ 983. Twenty-fifth Defence: Res Adjudicata.

The twenty-fifth defence consists in an averment that whatever cause of action may have once subsisted in favor of the plaintiff against the defendant, it has now been merged in, or extinguished by, a lawful judgment. The doctrine of res adjudicata is fully applicable to cases of infringement. The recovery of a judgment by the plaintiff against the defendant for a given act of infringement changes the character of the plaintiff's claim from tort to contract, and when the judgment has been satisfied destroys it altogether. This defence is, therefore, proper when a second suit is instituted between the same parties on an infringement for which the plaintiff has already recovered a judgment against the defendant.1 A judg

3 That no release is valid unless the releasor had at the time the legal right to grant it, see Goodyear v. McBurney (1853), 3 Blatch. 32.

That where in a suit by a patentee on behalf of a licensee the defendant sets up a release from the patentee, it will not avail him if the license was granted before the release, and this fact will be sufficient upon replication, see Goodyear v. McBurney (1853), 3 Blatch. 32.

That a fraudulent release is invalid, see 2 Pars. Cont. 715.

That an infringer, taking a release from one owner of a patent, receives it with notice of, and subject to, the equities of the other owners, see Kearney v. Lehigh Valley R. R. Co. (1886), 27 Fed. Rep. 699.

That a conditional release is no defence unless the conditions have been performed, see 2 Pars. Cont. 714.

That a release destroys the cause

of action and prevents the application of the remedy, see 2 Pars. Cont. 713.

§ 983. 1 That a former recovery is a bar to a new suit for the same cause of action, see Lyon v. Perin & Gaff Mfg. Co. (1888), 43 O. G. 983; Puetz v. Bransford, (1887), 41 O. G. 353; 32 Fed. Rep. 318; Cromwell v. County of Sac (1876), 94 U. S. 351.

For the effect of a recovery against one joint infringer, see § 948, note 3, ante.

That the wrongful sale of an invention is a tort for which the plaintiff can recover in a tort action, or by waiving the tort in assumpsit for the price received; and in the latter case no one could at any time be sued, if recovery were once had against the seller, see Steam Stone Cutter Co. v. Sheldons (1883), 15 Fed. Rep. 608; 24 O. G. 703; 21 Blatch. 260.

That a recovery from a maker is no

ment in favor of the defendant in a suit for an infringement is equally conclusive on the rights of the parties, and estops the plaintiff from any subsequent assertion of his claim.2 The judgments in both these cases must have been final judgments, rendered on the merits, and covering the same issue of infringement. Interlocutory decisions and judgments in

defence to the vendee unless the judgment against the maker has been satisfied, and included the article sold to the vendee, and a plea not alleging such satisfaction discloses no defence, see Fisher v. Consolidated Amador Mine (1885), 25 Fed. Rep. 201; 11 Sawyer, 190.

That a judgment and payment of nominal damages by one defendant, in a suit brought by the patentee without joining his licensee, for making and selling one machine are no bar to a suit by the patentee and licensee, for the benefit of the licensee, against the vendee of such defendant for using the same machine, see Birdsell v. Shaliol (1884), 112 U. S. 485; 30 O. G. 261.

2 That a decree of invalidity in the Federal courts is conclusive on the parties, see Hawks v. Swett (1875), 4 Hun, 146; 6 Thomp. & C. 529.

That a former judgment on the same title may be a bar if specially pleaded, though some of the parties are different, see Richardson v. Lockwood (1870), 4 Clifford, 128.

That a final decision in an interference is conclusive between the parties until reversed or affected by equity proceedings under Sec. 4915, Rev. Stat., see Peck v. Collins (1877), 70 N. Y. 376.

That a decree by consent on an issue of title is res adjudicata as to all the parties, see Tomkinson v. Willets Mfg. Co. (1884), 31 O. G. 918; 23 Fed. Rep. 895; 32 O. G. 382; Ex parte Pentlarge (1879), 17 Blatch. 306; Bann. & A. 607.

suit between the plaintiff's assignor and the present defendant is res adjudicata, see United States Metallic Packing Co. v. Tripp (1887), 39 O. G. 1554; 31 Fed. Rep. 350.

That a judgment works an estoppel only as to the matters controverted and decided, see Steam Gauge & Lantern Co. v. Meyrose (1886), 36 O. G. 1477; 27 Fed. Rep. 213.

That the judgment of a State court as to the contract relations of the parties is not res adjudicata on questions of title in the Federal courts, see Oliver v. Rumford Chemical Works (1883), 109 U. S. 75; 25 O. G. 784.

3 That a judgment of non-infringe ment is no bar to another action between the same parties for a different infringing act, see Steam Gauge & Lantern Co. v. Meyrose (1886), 27 Fed. Rep. 213; 36 O. G. 1477.

That though the Supreme Court has decided that a machine does not infringe an original patent it may still be an infringement of the re-issue, see Wells v. Jacques (1874), 5 O. G. 364; 1 Bann. & A. 60.

That a judgment is not conclusive on a plaintiff in favor of a licensee under his victorious rival, when afterward sued by him, if the license were granted before the judgment was rendered, see Ingersoll v. Jewett (1879), 16 Blatch. 378; 4 Bann. & A. 361.

That a judgment between two paten. tees on the question of priority affects the title of the junior patentee, but a judgment that the senior patentee was not the first inventor of an invention not That a decree by consent in a former claimed by the junior patent, does not

4

collateral proceedings, although disposing of the suit then pending, do not fall within the reason or the definition of this doctrine, and cannot be available as a defence on the main issues of the suit.1

§ 984. Defendant may Employ all his Defences unless Estopped. Any or all of the foregoing defences may be set up by the defendant in an action for infringement, unless he is himself estopped from urging them. The defendant is bound by his prior conduct equally with the plaintiff, and is not permitted to assume positions inconsistent with those which he has previously occupied and on which the plaintiff has relied in the direction of his own affairs.2 Thus a former owner of the patent, through whom the plaintiff's title was derived, cannot deny its validity when sued for its infringement, although it is