clogging the machine. The sets of rollers were so arranged by appellant that the lead line, in converging and ascending, pressed only against the side on which there was contact, and was held in place and operative by this one-sided pressure against the rollers, as points of contact. Is the inventor of such a decided improvement in the art entitled to the protection of the doctrine of mechanical equivalents, though the result is accomplished by a combination of elements, all of which are old, and the patent is a secondary rather than a primary one in the art?
In the case of National Hollow Brakebeam Co. v. Interchangeable Brakebeam Co., 106 Fed. 693, 45 C. C. A. 544, the Circuit Court of Appeals for the Eighth Circuit said:
“One who invents and secures a patent for a machine or combination, which first performs a useful function, is thereby protected against all machines and combinations which perform the same function by equivalent mechanical devices ; but one who merely makes and secures a patent for a slight improvement on an old device or combination, which performs the same function after as before the improvement, is protected against those only who use the very device or improvement he describes or mere colorable evasions thereof. In other words, the term ‘mechanical equivalent,’ when applied to the interpretation of a pioneer patent, has a broad and generous signification, while its meaning is very narrow and limited when it conditions the construction of a patent for a slight and almost immaterial improvement. Adams Electric R. Co. v. Lindell R. Co., 77 Fed. 432, 440, 23 C. C. A. 223, 231, 40 U. S. App. 482, 498; Stirrat v. Manufacturing Co., 61 Fed. 980, 981, 10 C. C. A. 216, 217, 27 U. S. App. 13, 42; McCormick v. Talcott, 20 How. 402, 405, 15 L. Ed. 930; Railway Co. v. Sayles, 97 U. S. 554, 556, 24 L. Ed. 1053; Brill v. Car Co., 90 Fed. 666, 33 C. C. A. 318, 62 U. S. App. 276.
“But-the great majority of patents falls between these two extremes. They are neither for pioneer inventions nor for improvements so slight as to be almost immaterial. While they do not evidence the first or the last step in the progress of the art to which they relate, they often mark signal advances and protect useful improvements. The doctrine of mechanical equivalents conditions the construction of all these patents, and in determining questions concerning them the breadth of the signification of the term is proportioned in each case to the character of the advance or invention evidenced by the patent under consideration, and is so interpreted by the courts as to protect the inventor against piracy and the public against unauthorized monopoly. Schroeder v. Brammer (C. C.) 98 Fed. 880; McSherry Mfg. Co. v. Dowagiac Mfg. Co., 41 C. C. A. 627, 101 Fed. 716, 721; Bundy Mfg. Co. v. Detroit Time-Register Co., 94 Fed. 524, 36 C. C. A. 375; Miller v. Manufacturing Co., 151 U. S. 186, 207, 14 Sup. Ct. 310, 38 L. Ed. 121; Penfield v. Chamber’s Bros. Co., 92 Fed. 639, 647, 34 C. C. A. 579, 587; McCormick Harvesting Machine Co. v. Aultman, Miller & Co., 69 Fed. 371, 16 C. C. A. 259, 37 U. S. App. 299; Muller v. Tool Co., 77 Fed. 621, 630, 23 C. C. A. 357, 366, 47 U. S. App. 189, 204.
“The doctrine of mechanical equivalents is governed by the same rules and has the same application when the infringement of a patent for a combination is in question as when the issue is over the infringement of a patent for any other invention. Schroeder v. Brammer (C. C) 98 Fed. 880; Imhaeuser v. Buerk, 101 U. S. 647, 653, 25 L. Ed. 945; Griswold v. Harker, 62 Fed. 389, 391, 10 C. C. A. 435, 437, 27 U. S. App. 122, 150; Thomson v. Bank, 53 Fed. 250, 253, 3 C. C. A. 518, 521, 10 U. S. App. 500, 509; Seymour v. Osborne, 11 Wall. 516, 542, 548, 20 L. Ed. 33; Gould v. Rees, 15 Wall. 187, 189, 21 L. Ed. 39; Fay v. Cordesman, 109 U. S. 408, 420, 3 Sup. Ct. 236, 27 L. Ed. 979; Water-Meter Co. v. Desper, 101 U. S. 332, 25 L. Ed. 1024; Gage v. Herring, 107 U. S. 640, 2 Sup. Ct. 819, 27 L. Ed. 601; Machine Co. v. Murphy, 97 U. S. 120, 24 L. Ed. 935; National Cash-Register Co. v. American Cash-Register Co., 53. Fed. 367, 373, 3 C. C. A. 559, 565, 3 U. S. App. 340, 357; Belding Mfg. Co. v. Challenge Corn-Planter Co., 152 U. S. 100, 14 Sup. Ct. 492, 38 L. Ed. 370.
“Mere changes of the form of a device or of some of the mechanical elements