Opinion of the Court.

ject matter of the first exception, I think the master was right in the conclusion he reached. The defendants were not charged on valves which were subsequently destroyed, or, if so, they were not charged upon the new valves which replaced them. See master's note 29, page 43 of master's report. The master properly disallowed the cost of destroyed valves."

Without going into details, it is sufficient to say that we concur in the conclusion that the defendant was not charged for valves which were subsequently destroyed, or, if so, it was not charged upon the new valves which replaced the destroyed valves.

As for the contention that the destroyed valves ought to form a credit against the profits actually realized by the defendant on other valves, it is sufficient to say that the only subject of inquiry is the profit made by the defendant on the articles which it sold at a profit, and for which it received payment, and that losses incurred by the defendant through its wrongful invasion of the patent are not chargeable to the plaintiff, nor can their amount be deducted from the compensation which the plaintiff is entitled to receive. The Cawood Patent, 94 U. S. 695; Elizabeth v. Pavement Co., 97 U. S. 126, 138; Tilghman v. Proctor, 125 U. S. 136.

The Circuit Court allowed interest on the $40,344.59 from the date of the filing of the master's report. The defendant assigns this as error, and contends that interest should have been allowed only from the date of the decree. In support of this view, the case of Mowry v. Whitney, 14 Wall. 620, 653, is cited. But we regard it as established by the cases of Illinois Central Railroad v. Turrill, 110 U. S. 301, 303, and Tilghman v. Proctor, 125 U. S. 136, 160, that the ruling as to interest made by the Circuit Court is proper. In the latter case, it is said: "By a uniform current of decisions of this court, beginning thirty years ago, the profits allowed in equity, for the injury that a patentee has sustained by the infringement of his patent, have been considered as a measure of unliquidated. damages, which, as a general rule, and in the absence of special circumstances, do not bear interest until after their amount has been judicially ascertained; and the provision introduced

Opinion of the Court.

in the patent act of 1870, regulating the subject of profits and damages, made no mention of interest, and has not been understood to affect the rule as previously announced. Silsby v. Foote, 20 How. 378, 387; Mowry v. Whitney, 14 Wall. 620, 651; Littlefield v. Perry, 21 Wall. 205, 229; Act of July 8, 1870, c. 230, § 55, 16 Stat. 206; Rev. Stat. § 4921; Parks v. Booth, 102 U. S. 96, 106; Railway Co. v. Root, 105 U. S. 189, 198, 200, 204; Illinois Central Railroad v. Turrill, 110 U. S. 301, 303. Nothing is shown to take this case out of the general rule. At the time of the infringement, the fundamental questions of the validity and extent of Tilghman's patent were in earnest controversy and of uncertain issue. Interest should therefore be allowed as in Illinois Central Railroad v. Turrill, just cited, only from the day when the master's report was submitted to the court (which appears, by the terms of his report and of the decree below, to have been October 7, 1884) upon the amount shown to be due by that report and the accompanying evidence."

Delay caused by the court, or not attributable to the plaintiff, in coming to a conclusion on the master's report, where the amount found by that report is confirmed, ought not to deprive the plaintiff of interest on the amount found by the master. Under such circumstances, the account ought to be considered as liquidated on the day when the master's report is filed. This is in analogy to the allowance of interest on the amount of the verdict of a jury from the date of the verdict to the date of the judgment, in accordance with the statutes of many States, and among others of Massachusetts. Pub. Stats. c. 171, § 8.

The decree of the Circuit Court is

Affirmed.

The CHIEF JUSTICE and MR. JUSTICE GRAY were not present at the argument, and took no part in the decision of this case,

Statement of the Case.

MCCREARY v. PENNSYLVANIA CANAL COMPANY

APPEAL FROM THE CIRCUIT COURT OF THE UNITED STATES FOR THE EASTERN DISTRICT OF PENNSYLVANIA.

No. 54. Submitted October 22, 1891.- Decided November 9, 1891.

In estimating, in a suit for the infringement of letters patent, the profits which the defendant has made by the use of the plaintiff's device, where such device is a mere improvement upon what was known before and was open to the defendant to use, the plaintiff is limited to such profits as have arisen from the use of the improvement over what the defendant might have made by the use of that or other devices without such improvement.

n inventor took out letters patent for an invention intended to accomplish a certain result. Subsequently he took out a second patent, covering the invention protected by the first, and accomplishing the same result by a further improvement. While holding both patents, he sued to recover damages for the infringement of the second, without claiming to recover damages for the infringement of the first. Held, that he could recover only for the injuries resulting from use of the further improvement covered by the second letters, and that if no such injury were shown the defendant would be entitled to judgment.

In

THIS was a bill in equity for the infringement of letters patent number 129,844, issued July 23, 1872, and reissued as number 5630, October 28, 1873, to the appellant, John McCreary, for an "improvement in coupling and steering apparatus." the specification of the reissue the patentee stated that his invention related "to certain improvements in devices for steering canal boats," etc., described in letters patent granted to Elijah and John McCreary, April 16, 1872, number 125,684, by means of which two boats are coupled together, and navigated and steered as one boat by means of a single steeringwheel. The invention described in said letters patent consisted, principally, "in coupling two boats together by means of a chain or rope passing around a steering-wheel on one boat, and around a system of sheaves or pulleys, and attached to the other boat, for the purposes of steering said boats as well as of coupling them; and in centring said boats together and form

Statement of the Case.

ing a universal joint between them by means of an overhanging guard or bumper on the stern of the forward boat, with a central notch therein, into which the projecting stem or cutwater of the rear boat fitted." "My improvements," says the patentee, consist, first, in coupling and centring said boats together and forming a universal joint between them by means of a chain, the two ends of which are fastened to opposite points on the stern of the forward boat and the central part to the stem or cutwater, or some central point on the bow of the rear boat, so as to hold its stem or cutwater against the overhanging guard or bumper of said forward boat, said chain serving to centre the boats without the necessity of any notch in the overhanging guard for the stem of the rear boat to fit into, and at the same time coupling and holding the boats together and forming a universal joint between them; second, in attaching the ends of the coupling and steering chains to the boats by means of crow-foot claw-hooks so as to render the chains easily adjustable, as hereinafter shown and described." He claimed as his invention:

"1. The combination of the two boats A and B, the steering. chain a passing around sheaves or pulleys, and around the windlass C, or its equivalent, the overhanging guard or bumper on the stern of the forward boat, and the chain D attached to opposite points on the stern of said boat and to the stem or central part of the bow of the rear boat, so as to form a universal joint between them, and keep them coupled and centred, substantially as shown and described.

"2. In combination with the boats A and B and the coupling and steering mechanism herein described, the claw-hooks hh, for attaching and adjusting the coupling and steering chains, substantially as set forth."

Upon the hearing in the Circuit Court an interlocutory decree was entered in favor of the plaintiff, finding the validity of the patent, and the infringement by the defendant, and ordering a reference to a master for an account of the "profits, gains and advantages which the said defendant has received or made, or which have arisen or accrued to it" from the said infringement, etc., but denying the injunction upon the ground, stated

Opinion of the Court.

in the opinion of the court, McCreary v. Pennsylvania Canal Co., 5 Fed. Rep. 367, that its allowance would cause much greater injury to the defendant than benefit to the plaintiff. A large amount of testimony was taken before the master, who reported that he found no proven profits, savings or advantages to have been received by or accrued to defendant from the manufacture, use or sale of the plaintiff's patented improvements. Exceptions were filed to this report, and upon the hearing of such exceptions a final decree was entered in accordance with the report, and that the plaintiff should recover his costs, except the costs of the accounting before the master, and the costs of the exceptions to the master's report, which were awarded to the defendant. The decree was subsequently amended by ordering that the defendant pay all the costs of the suit. From the decree denying the recovery of profits and damages an appeal was taken to this court.

Mr. Charles Sidney Whitman for appellant.

Mr. S. S. Hollingsworth for appellee.

MR. JUSTICE BROWN, after stating the case, delivered the opinion of the court.

About three months prior to the patent in suit, and on April 16, 1872, another patent, numbered 125,684, was issued to Elijah and John McCreary, for "an improvement in steering devices for canal boats," etc., which covered a similar coupling together of boats, barges and scows by means of a vertical groove formed in the overhanging stern guard or bumper of the forward boat, which groove was entered by the cutwater of the rear boat, a chain being used for connecting the boats, which chain was so connected with a train of gear-wheels placed in the rear boat as to enable both boats to be steered by means of a windlass. The first claim of this patent was as follows:

"1. Two boats or barges, A and B, fitted together by means of a projecting cutwater fitting into a notch in an overhanging guard, as described, and coupled and steered by means of a