not sustained." Counsel for respondent do not contend that the Liddell invention is primary within the definition given of that term by petitioner. Their concession is that it is "not basic in the sense of covering the first machine ever produced to make self-opening square bags by machinery." They do contend, however, that it is one of high rank, and if it be given a "fair construction and scope, no matter whether we call it basic, primary or broad, or even merely entitled to be construed as covering obvious mechanical equivalents, the question of infringement of the claims in suit by petitioner's machine becomes mechanically, and from a patent law standpoint, a simple one, in spite of slight differences of operation, and of reversal of some of the moving parts." The lower courts did not designate the invention as either primary or secondary. They did, however, as we shall presently see, decide that it was one of high rank and entitled to a broad range of equivalents. It becomes necessary, therefore, to consider the point of law upon which petitioner contends the question of infringement depends.

The citation is from Cimiotti Unhairing Company v. American Fur Refining Company, 198 U. S. 399, and the Kokomo Fence Machine Case, 189 U. S. 8, was adduced to sustain the proposition. But the whole opinion must be considered, and it will be seen from the language which we shall presently quote that it was not intended to say that the doctrine of equivalents applied only to primary patents.

We do not think it is necessary to follow counsel for petitioner in his review of other cases which, he urges, sustain his contention. The right view is expressed in Miller v. Eagle Manufacturing Company, 151 U. S. 186, 207, as follows: "The range of equivalents depends upon the extent and nature of the invention. If the invention is broad and primary in its character, the range of equivalents will be correspondingly broad, under the liberal construction which the courts give to such inventions." And this was what was decided in Kokomo Fence Machine Case, supra, Cimiotti Unhairing Com

pany v. American Fur Refining Company, supra, and Computing Scale Company v. Automatic Scale Company, 204 U. S. 609. It is from the second of those cases, as we have seen, that the citation is made which petitioner contends the point of law upon which infringement depends is formulated; but it was said in that case: "It is well settled that a greater degree of liberality and a wider range of equivalents are permitted where the patent is of a pioneer character than when the invention is simply an improvement, may be the last and successful step, in the art theretofore partially developed by other inventors in the same field.”

It is manifest, therefore, that it was not meant to decide that only pioneer patents are entitled to invoke the doctrine of equivalents, but that it was decided that the range of equivalents depends upon and varies with the degree of invention. See Ives et al. v. Hamilton, Executor, 92 U. S. 426; Hoyt v. Horne, 145 U. S. 302; Deering v. Winona Harvester Works, 155 U. S. 286; Walker on Patents, § 362; Robinson on Patents, $258.

We start, then, with the proposition that the Eastern Company may invoke for the Liddell patent the doctrine of equivalents, but without deciding now how broadly, we proceed to the consideration of the question of infringement. Invention is conceded to the Liddell machine, as we have seen, by the Continental Company. The concession, however, is qualified by the assertion that it covers only a "margin of differentiation" from the prior art. The Circuit Court and the Circuit Court of Appeals had a higher estimate of it. The Circuit Court said that the nature of its invention "was clear was disconnected from what precedes it by such a hiatus, that, if the claims are as extensive as the invention, there is no difficulty so far as concerns the application to the case of the rules with reference to equivalents." And answering the contention that it was the twentieth in the line of patents in its branch of the arts, and that it should be limited to the details described in its specifications, it was said that there was "such

a hiatus between them and what appears on the face of the Liddell patent, that they have no effect either in narrowing or broadening the alleged Liddell invention." The Circuit Court of Appeals affirmed the decree of the Circuit Court. It was less circumstantial than the Circuit Court in describing the invention. It said, however, after stating the claims, that their breadth "would imperil the patent, were the real invention less broad; but the defendant (the Continental Company) has not pointed out, and we have been unable to find, any operative combination of a rotary cylinder and forming plate oscillating thereon earlier than the patent in suit. If, therefore, the patent is valid, it has a wide scope, and the mechanical arrangement used by the defendant is fairly within its terms." The lower courts, therefore, found that the invention was a broad one and that the machine used by the Continental Company was an infringement. And these were questions of fact upon which, both of the courts concurring, their findings will not be disturbed, unless clearly wrong. See the case of La Bourgogne, ante, p. 95. To decide the question of invention an examination of the prior art was necessary and a consideration of what step in advance of that art, if any, the Liddell patent was. To decide the question of infringement a comparison of the Liddell machine with the machine used by the Continental Company was necessary and a determination of their similarity or difference. What was involved in these inquiries of fact and the conclusions from them is indicated by a record of many hundred pages of expert testimony and exhibits.

We shall proceed, then, to consider upon what grounds the Circuit Court and Circuit Court of Appeals proceeded and their sufficiency to sustain the judgments rendered within the rule announced.

The bill alleges the infringement of claims 1, 2 and 7. The courts below selected claim 1 for consideration, as determinative of the questions arising, as well on the other two claims as on it. In this counsel for the Continental Company ac

quiesced. Claim 1 is as follows: "In a paper bag machine, the combination of a rotating cylinder provided with one or more pairs of side forming fingers adapted to be moved toward or from each other, a forming plate also provided with side forming fingers adapted to be moved toward or from each other, means for operating said fingers at definite times during the formative action upon the bag tube, operating means for the forming plate adapted to cause the said plate to oscillate about its rear edge upon the surface of the cylinder during the rotary movement of said cylinder, the whole operating for the purpose of opening and forming the bottom of the bag tube, and means to move the bag tube with the cylinder.'

"The pith of the invention," the Circuit Court said, "is the combination of the rotary cylinder with means of operating the forming plate in connection therewith, limited, however, to means which cause the plate to oscillate about its rear edge." The court expressed the opinion that the invention extended to every means by which that result could be at

12. In a paper bag machine, the combination of the rotating cylinder provided with one or more pairs of side folding fingers adapted to be moved toward or from each other, a forming plate also provided with side forming fingers adapted to be moved toward or from each other, means for operating said fingers at definite times during the formative action upon the bag tube, operating means for the forming plate adapted to cause the said plate to oscillate about its rear edge upon the surface of the cylinder during the rotary movement of said cylinder for the purpose of opening and forming the bottom of the bag tube, a finger moving with the forming plate for receiving the upper sheet of the tube and lifting it during the formative action, power devices for returning the forming plate to its original position to receive a new bag tube, and means to move the bag tube with the cylinder.

7. In a paper bag machine, the combination of the rotating cylinder for the bag tube provided with one or more pairs of folding fingers adapted to be moved toward or from each other, a forming plate also provided with forming fingers adapted to be moved toward or from each other, means for operating said fingers at definite times during the formative action upon the bag tube, operating means for the forming plate adapted to cause the said plate to oscillate about its rear edge upon the surface of the cylinder during the rotary movement of said cylinder for the purpose of opening and forming the bottom of the bag tube, and connecting mechanism for timing the movements of the rotating cylinder and the forming plate.

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tained, and rejected the contention of the Continental Company that the invention was no broader than the details described in the specification. The court said that it was unable to see upon what the proposition could be based. And further said that there was nothing in the prior art which either broadened or narrowed the Liddell invention. "If any of the nineteen patents which had been put in evidence," the court added, "pointed out any form of combining the forming-plate with a rotating cylinder, they would of course narrow what Liddell could claim; but they have nothing of that kind." And speaking of the claims and their limitation by the description, it was said: "Nothing in the manner in which the claims are expressed adopts as the elements the detailed description contained in the specification. So far as the details of the description are concerned, they come within the ordinary rule of preferable method."

We think it is clear that the court considered that Liddell sought to comply with § 4888 of the Revised Statutes.1 In other words, he filed a description of his invention, explained its principle and the best mode in which he "contemplated applying that principle," and did not intend to give up all other modes of application. An inventor must describe what he conceives to be the best mode, but he is not confined to that. If this were not so most patents would be of little worth. "The principle of the invention is a unit, and invariably the

1 SEC. 4888. Before any inventor or discoverer shall receive a patent for his invention or discovery, he shall make application therefor, in writing, to the Commissioner of Patents, and shall file in the Patent Office a written description of the same, and of the manner and process of making, constructing, compounding, and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art or science to which it appertains, or with which it is most nearly connected, to make, construct, compound, and use the same; and in case of a machine, he shall explain the principle thereof, and the best mode in which he has contemplated applying that principle, so as to distinguish it from other inventions; and he shall particularly point out and distinctly claim the part, improvement, or combination which he claims as his invention or discovery. The specification and claim shall be signed by the inventor and attested by two witnesses.