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$ 48. What is infringement. Since the Patent Act gives to the patentee, his heirs and assigns, during the life of the patent, the exclusive right to make, use and vend the invention or discovery throughout the United States and the territories thereof (1), any unauthorized making, using or vending of the patented invention in the United States or its territories, during such time, is an infringement of the patent (2).

Wherever it is clear that the device or process used by the defendant in an infringement suit is the identical device or process described and claimed in the patent, the question of infringement is of course free from doubt, but in several other cases, which will be discussed below, it has been determined that the defendant has used the patented invention, and infringement has been found, although his device or process was not identically the same as that described and claimed in the patent.

§ 49. Colorable deviation. It is infringement to use a mere colorable variation of the patented device or process. Whether or not an alleged infringing device is merely a colorable variation, or is so substantially different from

(1) U. S. R. S., § 4884.
(2) Goodyear Shoe Mach. Co. y. Jackson, 112 Fed. 146.

the patentee's device as to be outside the scope of his claims, is a question of fact to be determined in each


If the mode of operation of an alleged infringing device or process is essentially different from that claimed in the patent, there is no infringement (3); but if the mode of operation is the same, there may or there may not be infringement, according to the determination of several other facts.

In the case of the Cawood patent (4), the complainant's machine for mending railroad rails consisted of an anvil having one of its end faces so shaped as to provide one of the jaws of a vice, between which and a movable jaw, the rail could be rigidly clasped and solidly supported. One of the alleged infringing machines (5) was provided with a pair of jaws similar to the Cawood jaws, but did not support the rail upon the anvil; and another (6) supported the rail upon the anvil but did not clasp it between vice-jaws, it being provided with two jaws which rested in a V-shaped notch in the anvil and were forced together by reason of their weight. Both of these machines were held to differ from the patented machine in their mode of operation, and to escape infringement on that ground. In this case the court used the following language: “To the inquiry, what constitutes an infringement, ... it is indispensable to keep in mind what the invention pat

(3) Walker on Patents, 8 341.

(4) Turrill V. Railroad Co., 1 Wall. 491; Cawood Patent, 94 U. S. 695.

(5) Id. at p. 705. (6) Id. at p. 706.

ented is. It is not ... any mode by which the result sought and obtained is secured but a machine that attains the desired end by means of described agencies, combined in a described manner and operating in a described way." And the alleged infringing machines in question were held not to operate in the way described in the patent.

§ 50. Substitution of equivalents. It is infringement to substitute for the elements of a machine, or of a process, their mechanical equivalents. An equivalent has been defined as something which performs the same function in the same manner, as the thing of which it is alleged to be an equivalent (7). It is such as a mechanic of ordinary skill, in the construction of similar machinery, having the plaintiff's specification and machine before him, could substitute in the place of the mechanism described without the exercise of the inventive faculties (8).

Examples are found in Whitney v. Mowry (9), where it was held that placing red-hot car wheels in a pit with alternate layers of charcoal, which was ignited thereby, for the purpose of annealing, was equivalent to placing the wheels in a previously heated furnace; and in Tilghman v. Morse, (10), where a patented process for engraving stone, metal, glass, etc., by a sand blast, the sand being impelled against the surface being treated by mechanical means, was held infringed by a similar process wherein the sand was impelled by gravity; and in

(7) Walker on Patents, Sec. 354. See § 15, above. (8) Burden v. Corning, Fed. Cas. No. 2143. (9) Fed. Cas. No. 17592. (10) Fed. Cas. No. 14044.

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Gibson v. Harris (11), where it was held that in a planing machine, two smooth plates of iron, operated on by a screw and spring, to keep the board on its bed, were the equivalents of the patentee's pressure rollers; and in Atlantic Giant Powder Co. v. Goodyear, (12), it was held that an explosive compound consisting of a combination of nitro-glycerine with infusorial earth was infringed by one in which the nitro-glycerine was mixed with a mealed powder composed of nitrate of soda, charcoal and sulphur, it appearing that the powder, as an ingredient, was substantially the same as the infusorial earth in function and effect, although possessed of additional advantageous qualities as well.

The last case above also affirmed the rule that when a substitute is used for one ingredient in a patented combination, which has every property, and performs every function of the original in the combination, it does not cease to be an equivalent because, in addition, it does something more, and does it better.

§ 51. Same (continued). The true criterion of mechanical equivalence is identity of purpose, and not of form or name; and this is a question of fact to be judged of on inspection; or on the testimony of experts. It is an inference to be drawn from all the circumstances by. attending to the consideration whether the contrivance used by one party is used for the same purpose, performs the same duties, or is applicable to the same object as the contrivance of the other party (13).

(11) Fed. Cas. No. 5396.
(12) Fed. Cas. No. 623.
(13) In re Boughton, Fed. Cas. No. 1696.

In invoking the doctrine of equivalents, a patentee who has made a primary invention is entitled to a more liberal application of the test of equivalency, than one who has made a secondary invention. A primary invention is one which performs a function never performed by any earlier invention; while a secondary invention is one which performs a function previously performed by some other invention, but which performs that function in a substantially different way from any that preceded it (14). Inventions of the latter kind are merely improvements over the devices or processes which pre ceded them.

In two cases laying down the rule of the preceding paragraph, it was said: “If the patentee be the original inventor of the device or machine called the divider, he will have a right to treat as infringers all who make dividers operating on the same principle, and performing the same function by analogous means or equivalent combinations, even though the infringing machine may be an improvement of the original, and patentable as such. But if the invention claimed be itself but an improvement on a known machine by a mere change of form or combination of parts, the patentee cannot treat another as an infringer who has improved the original machine by use of a different form or combination performing the same functions. The inventor of the first improvement cannot invoke the doctrine of equivalents to suppress all other improvements which are not mere colorable invasions of the first” (15). And: “In such cases, if

(14) Walker on Patents, Sec. 359.
(15) McCormick v. Talcott, 20 How. 405.

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