Opinion of the Court. the machine passes to the hands of the purchaser it is no longer within the limits of the monopoly. It passes outside of it, and is no longer under the protection of the act of Congress." In Adams v. Burke, 17 Wall. 453, it was held that "where a patentee has assigned his right to manufacture, sell and use within a limited district an instrument, machine or other manufactured product, a purchaser of such instrument or machine, when rightfully bought within the prescribed limits, acquires by such purchase the right to use it anywhere, without reference to other assignments of territorial rights by the same patentee;" and that "the right to the use of such machines or instruments stands on a different ground from the right to make and sell them, and inheres in the nature of a contract of purchase, which carries no implied limitation to the right of use within a given locality." Mr. Justice Bradley, with whom concurred Mr. Justice Swayne and Mr. Justice Strong, dissented, holding that the assignee's interest "was limited in locality, both as to manufacture and use." The right which Hecht had to make and sell the burners in Germany was allowed him under the laws of that country, and purchasers from him could not be thereby authorized to sell the articles in the United States in defiance of the rights of patentees under a United States patent. A prior foreign patent operates under our law to limit the duration of the subsequent patent here, but that is all. The sale of articles in the United States under a United States patent cannot be controlled by foreign laws. This disposes of the second error relied on. This brings us to the consideration of the damages reported. by the master, which report was confirmed by the court; and we are met on the threshold by the objection that the exceptions taken in the Circuit Court were not sufficiently specific to entitle appellants to raise the questions here upon which they submit argument. These exceptions are as follows: "First exception. For that the said master has in and by his said report certified on page six thereof that 'the cap was Opinion of the Court. the essential feature of the Gräff burner. The respondents adopted Gräff's arrangement, and then reduced the price of the burner, forcing Gräff to do the same in order to hold his trade. The evidence shows that the reduction in prices by Gräff was solely due to the respondents' infringement. So far as the evidence shows, the only competitors with Gräff in the use of his cap arrangement during the period covered by the accounting, were the respondents;' whereas the said master ought to have certified that respondents came innocently into possession of the burners by purchase in the ordinary course of business from legitimate manufacturers thereof in Germany, and that immediately upon being notified that they were claimed to be an infringement they ceased to sell the same. The evidence shows that at about the time Gräff made the alleged reduction in the price of his burners there were thrown upon the market lamp-burners of other kinds of equal or greater power, which came directly in competition with the Gräff burner, and that the reduction in price was the result of such competition; that the sale of 14 infringing burners by respondent in the course of three years' trade could not have been a sufficient competition to plaintiff's business to cause him to make a reduction of price, where the testimony shows that during the period from March 1st, 1886, when complainant reduced the price of burners, until October 31st, 1887, he sold about 6000 of said burners. "Second exception. For that the said master hath certified 'that the amount of damages which the complainant has suffered and sustained from and by reason of said infringement is two thousand nine hundred and seventy dollars and fifty cents;' whereas he should have reported nominal damages. "In all which particulars the report of the said master is, as the said respondent is advised, erroneous, and the said respondent appeals therefrom to the judgment of this honorable court." It is conceded that these exceptions raise two points, namely, that the infringement was not wilful, and that the reduction of prices was not caused solely by it. And this, as it seems to us, is quite sufficient to permit the real question Opinion of the Court. involved to be passed upon. The master awarded $2970.50 as damages for the reduction in price, which, he holds, was caused by the respondents' infringement. He says: "After the reduction in his prices, complainant sold, at wholesale, one thousand three hundred and twelve ten-wick burners, at a price twenty-five cents less on each than his orig inal price; four hundred and fifty twelve-wick burners, at fifty cents less; five hundred and ninety-two sixteen-wick burners, at seventy-five cents less; and seven hundred and sixteen twenty-wick burners, at seventy-five cents less; a total difference between the original and the reduced prices of one thousand five hundred and thirty-five dollars and fifty cents. "In addition, he sold at retail, on an average, five burners on each of the five hundred and seventy-four business days between the time when his prices were first reduced and October 31st, 1887; the number of burners thus sold being two thousand eight hundred and seventy, which were sold at a minimum reduction of fifty cents each under original prices a total difference between the original and the new prices of fourteen hundred and thirty-five dollars; which sum, added to the said sum of one thousand five hundred and thirty-five dollars and fifty cents, gives an aggregate amount of two' thousand nine hundred and seventy dollars and fifty cents." The report of a master is merely advisory to the court, which it may accept and act upon in whole or in part, according to its own judgment as to the weight of the evidence. Kimberly v. Arms, 129 U. S. 512, 523. Yet, in dealing with exceptions to such reports, "the conclusions of the master, depending upon the weighing of conflicting testimony, have every reasonable presumption in their favor, and are not to be set aside or modified unless there clearly appears to have been error or mistake on his part." Tilghman v. Proctor, 125 U. S. 136, 149. We think there was error here within that rule. Where the patentee granted no licenses, and had no estab lished license fee, but supplied the demand himself, and was able to do so, an enforced reduction of price is a proper item of damages, if proven by satisfactory evidence. Yale Lock VOL. CXXXII-45 Opinion of the Court. Manufacturing Co. v. Sargent, 117 U. S. 536. The damages must be actual damages, but where the patented feature is the essential element of the machine or article, as in the case just cited, if such damages can be ascertained they may be awarded. When, however, a plaintiff seeks to recover because he has been compelled to lower his prices to compete with an infringing defendant, he must show that his reduction in prices was due solely to the acts of the defendant, or to what extent it was due to such acts. Cornely v. Marckwald, 131 ́U. S. 159. There must be some data by which the actual damages may be calculated. New York v. Ransom, 23 How. 487; Rude v. Westcott, 130 U. S. 152. The master reported "that the number of lamp burners proven to have been sold by respondents, containing the invention claimed in and by the first claim of complainants' letters patent, is fourteen, provided that only the capped burners sold contain said invention, and that the number is one hundred and fourteen, if the half-capped burners so sold are to be held to contain said invention." The evidence established that the first invoice of lamp burners contained fifty 20-wick burners with caps, of which respondents sold four; and fifty 12-wick burners with half caps, of which respondents sold twelve; and fifty 16-wick burners with half caps, of which respondents sold forty-four; and that respondents altered the forty-six remaining 20-wick burners by changing their caps to half caps, and sold forty-four. This makes the one hundred with half caps, referred to by the master. Of the second invoice, the respondents sold four 20wick capped burners and six 16-wick capped burners, making, with four 20-inch burners with caps sold out of the first invoice, the fourteen capped wick burners reported as thus disposed of. The original bill in this case was filed September 17, 1886. It had been preceded by another suit, which had been dismissed. The goods in the second invoice, it is testified, had been ordered before this suit was commenced, but the invoice is dated October 16, 1886. This invoice contained one hundred 20 and one hundred 16-wick burners with caps, of which respondents sold four 20-wick and six 16-wick burners unchanged as before Opinion of the Court. stated. Most of this lot were still on hand at the time the testimony was taken, though some had been altered into what was called the "Boesch burner," which had no caps at all, and sold as such. The evidence tends to establish a profit of $1.85 on the 20-wick burners; $1.50 on the 16-wick; and 75 cents on the 12-wick. This would show a profit of $23.80 on the fourteen capped burners, being eight 20-wick and six 16-wick burners; and a profit of $156.40 on the one hundred half capped burners, being forty-four 20-wick, forty-four 16-wick and twelve 12-wick burners. Respondents had been advised by their counsel that the burners with half caps were not an infringement. The cap was the invention in question. The claim infringed, as already seen, was a combination, with the, guide tubes, of a ring-shaped cap provided with openings for the wicks, said cap being applied to the upper ends of the guide tubes, so as to close the intermediate spaces between the same. The half cap admitted the air directly to each wick, and in that respect differed from the claim of the patent. It is argued, however, with much force on behalf of the appellees, that the difference was a difference in degree and not in kind, as the air reached the wick when the full cap was used, and the functions of the latter as a strengthening band, a protector of the tops of the tubes, and in other particulars, were performed by the half cap; and this position is not resisted by counsel for appellants. But assuming that the sale of one hundred burners with half caps was an infringement, we are not prepared to concede that the sale of one hundred and fourteen burners under the circumstances detailed could have had the effect in compelling a reduction of price which has been ascribed to it. It is remarked by the master that "it is a fact of common knowledge that there is to be found on sale in the market a great variety of lamp burners, among which, as shown by the evidence, have been for many years burners of the same general class as complainants'." This being so, and Boesch & Bauer being dealers in burners generally, it is not to be presumed that Gräff reduced his prices, for nineteen months, |