The usual and frequently the only adequate remedy, in case of the invasion of the exclusive rights secured by letters patent, is a suit in equity for an injunction and an accounting of profits.4 Where the patent has expired, however, relief in equity is ordinarily not obtainable; and in any event the patentee may sue the infringer at law as a tort-feasor and recover compensatory damages.1 Since the tort is one which benefits the wrongdoer, it has been supposed that the patentee may elect to sue in assumpsit for restitution.2 But the rights and remedies of a patentee are created and defined by Congress, and the only action at law provided for by the statute is an action on the case for damages.3 Whether this includes an action in assumpsit for restitution may be doubted.4 It may be noted, however, that if an action for restitution is allowable, the true measure of recovery is not the profits actually reaped by the infringer, as in the case of a suit in equity for an injunction and accounting, but the value of the use of the invention - ordinarily determined by reference to the royalty or price paid for such use by licensees. For it is only to the extent of the value of the use that the infringer is benefited at the patentee's expense.

Albright, 1908,14 N. M. 345; 93 Pac. 717, aff. 1910, 216 U. S. 331; 30 S. Ct. 318; Nichols v. MacLean, 1886, 101 N. Y. 526; 5 N. E. 347; 54 Am. Rep. 730'; Hudgens v. Kennedy, 1850, 5 Strob. (S. C.) 44. See Mechem, "Public Officers," Sec. 333, and other cases there cited; 29 Cyc. 1394, n. 74. Contra: Stuhr v. Curran, 1882, 44 N. J. L. 181; 43 Am. Rep. 353.

1 United States v. Addison, 1867, 6 Wall. (U. S.) 291. And see Fitzsimmons v. City of Brooklyn, 1886, 102 N. Y. 536; 7 N. E. 787; 55 Am. Rep. 835. But necessary expenses of maintaining office may be deducted: Sandoval v. Albright, 1908, 14 N. M. 345; 93 Pac. 717, aff. 1910, 216 U. S. 331; 30 S. Ct. 318; Kreitz v. Behrensmeyer, 1894,149 111. 496; 36 N. E. 983; 24 L. R. A. 59; Mayfield v. Moore, 1870, 53 111. 428; 5 Am. Rep. 52.

2 Kreitz v. Behrensmeyer, 1894, 149 111. 496, 503; 36 N. E. 983; 24 L. R. A. 59.

3 Boyter v. Dodsworth, 1796, 6 Term R. 681. 4 U. S. R. S. Sec. 4921.