after stating the facts, delivered the opinion of the court.
The evidence is convincing, as well as undisputed, that the three-wheel combination of the Bates patent achieved success and popularity in the production of barbed wire, with great improvement in the speed and accuracy of the operation, and thus made desirable advance in the barb-wiring art. In reference to the contention that the patent is invalid for want of invention—that it involved “nothing more than mechanical skill” to so improve the two-wheeled combination disclosed in an earlier patent, No. 270,646, issued to Edenbom & Griesche in 1883—it is sufficient to remark that the assumed prototype for the use of two butterfly-wheels was a failure, and Bates was the pioneer in his conception of a three-wheel combination, which solved the problem where other inventors had failed in the quest. Exact measurement of the faculty thus brought to the solution is needless in the face of this undeniable achievement. The combination so devised is both new and useful in “ the sense and within the objects of the patent law, and its patentable novelty is substantially conceded by a leading expert, testifying on behalf of the appellee. That it was patentable subject-matter is undoubted.
In the subsequent device of Fredrich, under which the appellee’s machine is made, three butterfly-wheels are used in a combination, with all the general characteristics and advantages of the Bates three-wheel combination, and differing only in certain details and transpositions, upon which escape from infringement is sought. The facts are neither complicated, nor disputed in any feature deemed material, and solution of the issue of infringement rests on the scope of the invention and claims in suit. The machines are alike in adopting the barbing devices and the twisting and spooling mechanism of the prior art. Both adopt the butterfly-wheel combination for delivering the barbed wire from one to the other of the mechanisms. The combination thus introduced automatically regulates the delivery for twisting and spooling, so that uniform tension is preserved in both operations, while the wire is reeled and accumulating upon the spool. No such effective device appears prior to that of Bates, and the want of it was well recognized as limiting the speed and reliability of the operation. With the Bates device the production was increased about 50 per cent., and the machines under the patent came into extensive use and popularity.
In the Bates machine the upper wheel, C°, is an oscillating wheel, mounted on a swinging arm, C2, oscillated by the crank, roller, C. The middle wheel, C8, has stationary bearings and is “the positively-driven wheel,” while the lower wheel, E, is an idler mounted on a yielding arm, E1, provided with a spring, V1, so that it will yield to and fro as the wire passes to the twister. In the appellee’s machine the three wheels are alike in general location, aside from individual function— 'the upper wheel oscillating, the middle wheel on stationary bearings, and the lower wheel on a yielding arm provided with a spring—with like' function of the combination in conveying the barbed wire to the twister and spooler. The • departures from the patent specifications, upon which the defense relies, are these: (1) Instead of driving the *121middle wheel, the power is applied to the lower wheel, so that it becomes “the positively-driven wheel,” and in this view it is mounted on a swinging arm attached above the wheel, instead of below, with the spring transposed accordingly, while the middle wheel is made the idler, which is, in the language of the appellee’s brief, “exactly the reverse of the case of the Bates patent”; and (2) while the lower wheel of Bates serves as an indicator of the tension for the operator to make adjustment with the friction brake, the appellee attaches the cord of the brake to the yielding arm, so that the motion of the arm automatically effects the adjustment.
1. The first-mentioned transposition of the functions of middle and lower wheels plainly evades the specific form of the combination described in the patent. It is true, as urged on behalf of the appellee, that it has “no middle positively-driven stationary” wheel, “no lower yieldingly mounted idler” wheel, and “no yielding butterfly-wheel arranged' between the positively-driven wheel and the spooler.” With the power transferred to the lower wheel and the middle wheel used as the idler, these descriptions are, of course, inapplicable, except in like reverse order, though the several elements and advantages of the patent combination are substantially appropriated. Obviously this change involves mere mechanical rearrangement of the driving means and yielding arm, and no difference in principle or result of the combined means and operation. The contentions that the alleged infringement is not an adaptation of the Bates three-wheeled combination, but is founded! upon and follows the teachings of the two-wheeled-combination of the prior Edenbom & Griesche patent (No. 270,646), and that it is, substantially, a new two-wheeled.combination, are without merit. True it is that the unsuccessful device of Edenbórn & Griesche shows two butterfly-wheels, one of which oscillates and the other is stationary and positively driven; but the third wheel of Bates’ device with its yielding-arm provision and results—conceded by the appellee’s expert to be novel and “substantive improvement”—neither appears nur is suggested in that patent. This essential element of the combination is equally distinguishable in the appellee’s machine for like effect, and is plainly derived from Bates. The three wheels are actually used in the alleged infringing machines, as equivalent means for equivalent objects, so that it is unnecessary to consider whether its idler wheel can be taken out and leave the machine operative, minus the function of the idler. If infringement thus appears, the owner of the patent cannot be denied relief, though protection may be limited by the terms of the claims to such three-wheel form. Du Bois v. Kirk, 158 U. S. 58, 66, 15 Sup. Ct. 729, 39 L. Ed. 895.
The conception of Bates was not pioneer invention in the broad sense of the term, and the mechanism described in the patent was merely an improvement upon old wire-barbing machines. Nevertheless the invention was meritorious—a marked advance in that art, and of unquestionable utility—so that the patentee is not only entitled to protection of his monopoly against colorable evasions, but, for such protection, is entitled as well to the benefit of the doctrine of equivalents, commensurate with the invention disclosed, though not of the broad range which is accorded *122an invention of primary character. Miller v. Eagle Manufacturing Co., 151 U. S. 186, 207, 14 Sup. Ct. 310, 38 L. Ed. 121, 12 Notes U. S. Rep. 487; Bundy Manufacturing Co. v. Detroit Time-Register Co., 94 Fed. 524, 540, 36 C. C. A. 375; National Hollow Brake Beam Co. v. Interchangeable B. B. Co., 106 Fed. 693, 710, 45 C. C. A. 544.
We are of opinion that the means thus transposed in the appellee’s machine, if not within the definition of colorable evasions which infringe the patent in any view of its scope, are plain appropriations of the essence of the Bates conception by equivalent means, and infringements of the patent within the well settled rule referred to. All the elements of the patent combination are employed with substantial identity in their use, and departure appears from the letter of the claims only, in the arrangement of these elements, without substantial difference in the principle of operation. The policy and rules of the patent law require that the patentee be protected against such evasions of the wording of a claim in form or nonessential details, when the substance of the invention is thus used and is unmistakably shown in the specifications and claims. Winans v. Denmead, 15 How. 330, 343, 14 L. Ed. 717, 5 Notes U. S. Rep. 331; Ives v. Hamilton, 92 U. S. 426, 431, 23 L. Ed. 494; Machine Co. v. Murphy, 97 U. S. 120, 125, 24 L. Ed. 935; and 9 Notes U. S. Rep. 533; Elizabeth v. Paving Co., 97 U. S. 126, 137, 24 L. Ed. 1000; Hoyt v. Horne, 145 U. S. 302, 308, 12 Sup. Ct. 922, 36 L. Ed. 713 ; Westinghouse v. Boyden Power Brake Co., 170 U. S. 537, 568, 18 Sup. Ct. 707, 42 L. Ed. 1136; International Mfg. Co. v. H. F. Brammer Mfg. Co. (C. C. A.) 138 Fed. 396, 400.
The form in which the middle and lower wheels respectively are arranged for use in the combination is not of the essence of the invention. Patentability resides in the combined use of the wheels, and to adapt one or the other to be driven, for the object in view was incidental only—a matter of mere mechanical choice and skill. To change the driving function from the stationary (middle) wheel to the yielding (lower) wheel corresponding changes of equipment to that end were, of course, needful, as exemplified in the appellee’s structure; but there is no substantial departure in principle or idea of means for the combination. With such “necessary rearrangement of the driving mechanism,” it is admitted in the testimony of the appellee’s expert that the yielding wheel of the Bates device can be made the driven wheel (while the middle wheel becomes the idler), and thus “operate as well as in the construction shown in the patent,” and that no reason appears why the “defendant’s machine would not operate perfectly” with the middle wheel “made the positively-driven wheel.”
Interchangeability is referred to in Miller v. Eagle Mfg. Company, supra, and other cases cited in the argument on behalf of the appellee, as an “important test in determining the question of infringement,” and it is contended that the interchangeability of parts and functions thus conceded does not meet the requirements for such test, upon the assumption that the interchange involves substantial reorganization of one and the other structure. This contention is without force, under our conclusion that these deviations are plain equivalents within the scope of the patent, and do not depart substantially from the invention. If the test *123is applicable to such cases of recombination, the corresponding arrangement of means is essential for its application, and in that view interchangeability appears for any value it may have in solving the issue. While the middle wheel is deprived of its function as a driven wheel, in the changed structure, it retains the function of regulating the tension of the wire in connection with the action of the top (oscillating) wheel, and is so employed in the alleged infringement. It is immaterial whether this benefit is of less importance in the appellee.’s structure, or whether the machine can be made operative without this wheel (Du Bois v. Kirk, supra), as difference in the degree of benefit will not authorize such use nor establish want of identity, in the sense of the patent law, of the means so combined. Moreover, in the Fredrich patent (No. 711,303), under which justification is sought for its use, this wheel is made an element of the claim and described as “a fixed intermediate guide-wheel over which the barb-wire travels for intermittently feeding the wire.”
The further argument that noninfringement must be presumed from the grant of the above-mentioned Fredrich patent is equally unsound upon the foregoing view of substantial identity in fact. Any inference so arising is, of course, rebuttable, and is rebutted in the present instance, as we believe, not only by the evidence referred to, but in the fact that subordination to the patent in suit appears to be expressly, recognized in the proceedings upon the Fredrich application, as shown in the file contents in evidence. On rejection of the original broad claims in that application, for conflict with the Bates patent, such claims were amended upon representation that the invention “was an improvement over the construction of Bates.”
2. The remaining contention, that the appellee’s device escapes infringement through its additional means and function in the automatic regulation of tension, does not impress us as tenable, under our conclusion that the three-wheel combination of the patent is appropriated, with all its results, as an entirety. In the testimony of one of the experts for the appellee the sole distinction between the devices in this feature is stated in plain terms. After mentioning the difficulties which had arisen in making barbed wire from want of uniformity in tension as the spooling progressed, the witness states: These evils “are corrected in the Bates machine” by “a rope, b1, which passes to the friction brake, x1, and is operated by the workman, in accordance with the indication afforded by the movement of the swinging spring-held arm which carries the third butterfly wheel”; while in the appellee’s machine “these same evils are corrected by a like rope which passes to the friction break,” and instead of operation by the workman, upon the indication given by the swinging arm, such arm “not only indicates the difference in tension, but automatically, with such indication, pulls the rope.” This is a mere •addition to the patented machine, supplementing the function of one element, without changing the co-operative function of the wheels in their combination. So, assuming that it is an important improvement (which is disputed in the appellant’s testimony), and patentable as an improvement, its association with the means of the prior patent is unauthorized without license from such patentee. Cochrane v. Deener, 94 U. S. 780, 787, 24 L. Ed. 139; Cantrell v. Wallick, 117 U. S. 689, 694, 6 Sup. Ct. *124970, 29 L. Ed. 1017; Hoyt v. Horne, 145 U. S. 302, 309, 12 Sup. Ct. 922, 36 L. Ed. 713; Walker on Patents (3d Ed.) § 347.
The alleged improver may have a valid patent for his new means, and is entitled to its exclusive use; but the prior patent equally excludes him. from the use of the prior invention, with or without his improvement. As expressed by Mr. Justice Bradley, in Cochrane v. Deener, supra, he cannot appropriate the earlier invention, “even though supplemented by and enveloped in very, important and material improvements” of his own. Each has the right to enjoy the monopoly awarded by his patent, but cannot be permitted to invade the limits of the other’s invention and patent privilege. The object of the law authorizing the grant is to stimulate invention by this reward to the inventor. It must be administered-in conformity with this liberal policy, as a wise exception from the common-law rule against monopolies. So the exclusive privilege of the patentee must be protected to the full extent of his invention and grant, while its limitations are to be strictly observed, to prevent interference, beyond the fair scope of valid grant, with improved means or other inventions, the promotion of which is the constant view of the patent policy. Within such limitations, however, the exclusion applies equally against the improver and the general public, and we are of opinion that the alleged improvement does not escape the patent.
The decree of the Circuit Court is reversed accordingly, with direction to enter a decree in favor of the appellant in conformity with this-opinion.