Where the question of patentable novelty in a device was by no means free from doubt, the court, in view of the extensive use to which the patent had been put by manufacturers of wagons, resolved the doubt in favor of the patentee and sustained the patent ; Topliff v. Topliff, 145 U. S. 156, 12 Sup. Ct. 825, 36 L. Ed. 658. While the utility of a contrivance, as shown by the general public demand for it when made known, is not conclusive evidence of novelty and inven tion, it is nevertheless highly persuasive in that direction, and in the absence of pretty conclusive evidence to the contrary, will gen erally exercise controlling influence; Hill v. Biddle, 27 Fed. 560; in doubtful cases only; Voigtmann v. Cornice Co., 148 Fed. 848, 78 O. C. A. 533 ; in case of doubt it will turn the scale; Krementz v. S. Cottle Co., 148 U. S. 556, 13 Sup. Ct. 719, 37 L. Ed. 558 ; it is better evidence of invention than the opinion of an expert or the intuition of a judge; Palmer v. Johnston, 34 Fed. 336; but not where public •acceptance is the plain result of successful business methods in creating a market for the article. And not when the popularity is not due to any patentable fea ture. The fact that a patented device went into immediate use, and supplanted all oth ers, cannot be attributed to artful advertis ing, in the case of an article such as an electric heater for railway cars, which is sold, not to the public, but to mechanicians of skill in their art; Consolidated C. H. Co. v. Heating Corp., 82 Fed. 993. But extensive use has been said to be an unsafe criterion of patentability; McClain v. Ortmayer, 141 U. S. 419, 12 Sup. Ct. 76, 35 L. Ed. 800. When, in a class of machines widely used, it appears that at least, after repeated and futile attempts, a machine has been con trived which accomplishes the result desired, and when a patent has been granted to the successful inventor, the courts should not be ready to adopt a narrow or astute construc tion, fatal to the grant; Keystone Mfg. Co. v. Adams, 151 U. S. 139, 14 Sup. Ct. 295, 38 L. Ed. 103.
Simplicity in the device is itself a merit ; 2 Webst. Pat. Cas. 113. Mere suggestions from others do not negative the existence of patentable invention, unless they cover the entire invention ; Hubbell v. U. S., 5 Ct. of Cl. 1. The suggestion by others of a part of a device does not show the absence of inventive skill as to the whole ; Worden v. Fisher, 11 Fed. 505. Where inventive skill was necessary in addition to suggestions of others, the inventor is entitled to a patent ; Union Paper-Bag Mach. Co. v. Pultz & Walk ley Co., 15 Blatcbf. 160, Fed. Cas. No. 14, 392; Alden v. Dewey, 1 Sto. 336, Fed. Cas. No. 153; O'Reilly v. Morse, 15 How. (U. S.) 62, 14 L. Ed. 601. To suggest that a cer tain result may be obtained, but without in dicating how, is not an invention; Graham v. Gammon, 'T Biss. 490, Fed. Cas. No. 5,668. Mere experiment 'is not invention; Many v. Sizer, 1 Fish. 17, Fed. Cas. No. 9,056.
The simplicity of a device and its apparent obviousness after the event, ought not to de tract from its meritoriousness. That it had never been suggested or thought of before, and effectually supplied the one thing neces sary to bring success, when before there had been nothing but failure, is sufficient within the meaning of the patent law ; McKay & C. L. Mach. Co. v. Dizer, 61 Fed. 102, 9 C. C.
A. 382. "The apparent •simplicity of a new device often leads an inexperienced person to think that it would have occurred to any one familiar with the subject ; but the deci sive answer that with dozens and perhaps hundreds of others laboring in the same field, it had never occurred to any one be fore. The practised eye of an ordinary me chanic may be safely trusted to see what ought to be apparent to every one." Potts v. Creager, 155 U. S. 597, 15 Sup. Ct. 194, 39 L. Ed. 275.
A "double use" may involve invention if the second use is an art remote from the former use; otherwise, if the new use is such that it would occur to a person of ordinary mechanical skill ; much depends upon the nature of the changes required to adapt the device to its new use ; id.
Study, effort, and experiment are not alone enough to constitute inventive skill; Butler v. Steckel, 27 Fed. 219. Nor is the exercise of good judgment; Estey v. Burdett, 109 U. S. 633, 3 Sup. Ct. 531, 27 L. Ed. 1058. Nor the exercise of the reasoning process ; Wat son v. Ry. Co., 23 Fed. 443. Inventive skill requires thought, while mechanical skill does not; Butler v. Bainbridge, 24 Blatch. 163, 29 Fed. 142. Small discoveries may involve in ventive skill; Hobbie v. Smith, 27 Fed. 656. If it exist in some degree, the courts will not measure it by an exacting standard ; Valvona v. D'Adamo, 135 Fed. 544.
The exercise of mechanical skill must be considered as it existed at the date of the invention ; Wilcox v. Bookwalter, 31 Fed. 224.
A mechanical equivalent exists where one device may be adopted instead of another by a person skilled in the art, from his knowl edge of the art; Johnson v. Root, 1 Fish. 351, Fed. Cas. No. 7,411. Equivalents have been said to be "obvious and customary" in terchanges; Smith v. Downing, 1 Fish. 64, Fed. Cas. No. 13,036.. It is a question of fact depending on the opinion of experts and on an inspection of the machine ; Foss v. Her , bert, 2 Fish. 31, Fed. Cas. No. 4,957. It is a question of use, not of name ; Graham v. Mason, 5 Fish. 1, Fed. Cas. No. 5,671. Equiva lents may differ in shape ; Graham v. Mfg. Co., 11 Fed. 148; a substitute in a combina tion does not cease to be an equivalent be cause, in addition, it does something more and better ; Atlantic Giant Powder Co. v. Goodyear, 3 B. & Ard. 161, Fed. Cas. No. 623. Only those things can be considered equiva lents for the elements of a manufacture which perform the same function in substantially the same way ; Goodyear Dental Vulcanite Co. v. Davis, 102 U. S. 222, 26 L. Ed. 149.
The test of equivalency is whether the sub stituted element operates in substantially the same way to produce substantially the same result ; Palmer v. Mach. Co., 186 Fed. 496. The docttine of equivalency may be invoked for other than pioneer patents, the range depending upon and varying with the degree of invention ; Continental Paper Bag Co. v. Paper Bag Co., 210 U. S. 405, 28 Sup. Ct. 748, 52 L. Ed. 1122. Where no inventive skill is shown in the substitute, it is an equiva lent ; Crouch v. Roemer, 10 U. S. 797, 26 L. Ed. 426.