The operation of this device is best shown by the foregoing skeleton drawings.

The auxiliary reservoirs are charged by air under pressure,*entering from the train pipe, raising and passing through the feeding-in valve piston, 26, and flowing slowly into and through the passage, A, to the auxiliary reservoir, until such reservoir is filled. In this condition the brake cylinder is emptied and opened to the atmosphere through the exhaust passage, G.

In order to apply the brakes gradually, so as to slacken speed or made an ordinary stop, air pressure in the train pipe is reduced slightly (say from 3 to 5 pounds) by action of the engineer's valve, and the reduction of pressure on the right side of the piston, 29, causes the piston to make what is termed a "preliminary traverse" to the position shown in diagram "Service Application." Such preliminary traverse pulls the stem slide valve, 18, to the right, and opens the apertures, i, j, and k (one of these apertures being to the right, and the other to the left, of valve 22), and through these apertures air rushes from the auxiliary reservoir to the brake cylinder; but the poppet valve, 22, still remains upon its seat.

If quick action be required, the pressure in the train pipe is suddenly lowered to the extent of 15 or 20 pounds, and the traveling piston, 29, instead of making a preliminary traverse to the intermediate position shown in the "Service Application," makes a full traverse to the extreme right, the effect of which is that the valve, 22, is pulled off its seat by the collar, M, and a large passage is opened to the brake cylinder under the valve, 22, and around the stem, 18. The result is, as shown in the last diagram, that not only does the air in the auxiliary reservoir escape in full volume to the brake cylinder, but air from the train pipe rushes directly to the brake cylinder through the large passage, F, into the chamber, C, and under valve, 22.

The argument of the defendants in this connection is that in this device there is no auxiliary valve or by-passage, but the quickaction result is effected simply by proportioning the ports and passages of the old triple valve, and using a fixed partition, 9, to divide the piston chamber, D, from the main-valve chamber, C; that it is this partition which produces the quick action, and that such partition is not a valve, nor the mechanical equivalent of a valve, but merely a metal ring screwed immovably into the triple-valve casing, and serving to divide the piston chamber from the main-valve chamber; that this partition was a new element, never before found in triple valves, and introduced a new principle and mode of operation, totally different from anything ever Invented by Mr. Westinghouse or any other inventor; and that its effect is to make valve, 22, termed by them the "main valve," admit the train-pipe air to the brake cylinder at 18 S.C.-46

the same time that it admits the auxiliary air thereto.

It is claimed that, in embodying this new principle, Mr. Boyden adopted the form of triple valve shown in the expired Westinghouse patent, No. 141,685 (1873), in which the main valve, 22, is of the poppet form, and the separate valve, 17, controlled by a rod sliding through the main valve, is employed for releasing the brakes. For charging the auxiliary reservoir, he adopted, from the expired Westinghouse patent, No. 144,006 (1873), a check-valved feed passage through the triple-valve piston, but arranged the feed passage and its check valve, 26, in a tubular extension, F, of the piston, and substantially in the form shown in Boyden patent, No. 280,285 (1883). He also provided a sensitive graduating valve, similar in results to the graduating valve, é, of the Westinghouse patent No. 220,556 (1879), by so arranging a small passage, 40, in the sliding stem, which actuates the release valve, that such passage will be opened and closed by the sliding of such stem through the main valve, 22. As thus constructed, the triple valve operates much the same as that of patent No. 220,556, and, like the latter, is incapable of quick action.

In both the complainants' and defendants' devices there is (1) a feeding-in valve to charge the auxiliary reservoir; (2) a valve, which complainants call their “main valve," and which the defendants denominate a "graduating valve," which is opened by the preliminary traverse of the piston to admit reservoir air to the brake cylinder; (3) a release valve which discharges air from the brake cylinder to the atmosphere; and (4) a quick-action valve,-41 in the complainants' patent, and 22 in the defendants',which is opened by the further traverse of the piston to admit train-pipe air to the brake cylinder. In defendants' patent it may also be used to admit auxiliary reservoir air to the brake cylinder.

*

One of the main controversies in the case turns upon the construction and operation of the poppet valve, 22, called by the defendants their "main valve." Complainants insist that the office of their main valve is performed by the stem slide valve, 18, of defendants' patent, and by its apertures, 1, j, and k, through which air passes from the auxiliary reservoir to the brake cylinder, and that the poppet valve, 22, is only called into action in emergency cases, when a large quantity of air is suddenly withdrawn from the train pipe, and the valve is unseated by the traverse of the piston to the extreme right.

There is no doubt that the function of admitting air from the auxiliary reservoir to the brake cylinder, which is performed in the Westinghouse patent by what the complainants term the "main valve" (aided, however, by the graduating valve) is, in ordinary cases, performed principally, if not

*565

*567

altogether, by the stem slide valve, 18, and Its three ports, i, j, k, of the Boyden patent, which defendants term their "graduating valve." It is equally clear that in emergencies, where quick action is required, air, which in the Westinghouse patent passes through auxiliary valve, 41 (opened by the further traverse of the piston), in the Boyden patent finds its way through the poppet valve, 22, which has also been lifted from its seat by the further traverse of the piston.

One of the mair, differences between the two devices is this: That in the preliminary traverse of the piston of the Westinghouse patent there is a movement first of the graduating valve to open its port from the auxiliary reservoir, and then of the main valve, carrying the graduating valve, also, with it, to open a passage to the brake cylinder, while in the Boyden patent it is only the graduating valve which is opened by the preliminary traverse of the piston. In doing this, the graduating valve moves through the poppet valve, but does not lift it from its seat. In emergency cases not only do the graduating valve and the main valve of the Westinghouse patent move as before, but by the extreme traverse of the piston the auxiliary valve, 41, is shoved from its seat, and a separate *passage is opened for the air from the train pipe to the brake cylinder. In the Boyden patent, however, the extreme traverse of the piston lifts the poppet valve from its seat, and opens a wide passage to the brake cylinder, not only for the air from the auxiliary reservoir, but, through the peculiar operation of the partition, 9, and its aperture, B, directly from the train pipe. As the graduating valve of the Boyden patent practically does all the work in ordinary cases, and the poppet valve is only called into action in emergency cases, the latter is practically an auxiliary valve, by which we understand, not necessarily an independent valve, nor one of a particular construction, but simply a valve which in emergency cases is called into the assistance of the graduating valve. In this particular the poppet valve of the Boyden device performs practically the same function as the slide valve, 41, of the Westinghouse. It is not material in this connection that it is a poppet valve, while the other is a slide valve, since there is no invention in substituting one valve or spring of familiar shape for another (Imhaeuser v. Buerk, 101 U. S. 647, 656); nor that in one case the piston pushes the valve off its seat, and in the other pulls it off; nor is it material that this poppet valve may have been used in prior patents to perform the function of a main valve, so long as it is used for a different purpose here. Indeed, this valve seems to have been taken bodily from Westinghouse patent No. 141,685, where it was used as a main valve, and the stem valve, 18, with its ports, i, j, k, added for ordinary uses, and

the poppet valve thus converted from a main valve to an auxiliary valve.

We have not overlooked in this connection the argument that the poppet valve, 22, is also sometimes used for graduating purposes; but it is not commonly so used, and appears to be entirely unnecessary for that purpose. It seems to be possible to move the piston, 29, to its extreme traverse so slowly, and hence to open valve, 22, so gradually, that the pressure in the chamber, C, will be reduced so slightly that the trainpipe air will not have sufficient force to throw open the check valve, 26; and hence in such case no train-pipe air will be admitted directly to the brake cylinder, which will be filled with*auxiliary reservoir air only. But, as a matter of fact, this seldom or never takes place in the practical operation of the device, and is an unnecessary and wholly unimportant incident, and for all practical purposes valve, 22, is solely a quick-action valve. As this valve is actuated by the piston of the triple valve, and in such action is independent of the main valve, it meets the demand of the first claim of the patent; and as it is actuated by the piston-stem, and controls communication between passages leading to connections with the main air pipe and with the brake cylinder, it seems also to be covered by the fourth claim.

But, even if it be conceded that the Boyden device corresponds with the letter of the Westinghouse claims, that does not settle conclusively the question of infringement. We have repeatedly held that a charge of infringement is sometimes made out, though the letter of the claims be avoided. Machine Co. v. Murphy, 97 U. S. 120; Ives v. Hamilton, 92 U. S. 431; Mory v. Lockwood, 8 Wall. 230; Elizabeth v. Pavement Co., 97 U. S. 137; Sessions v. Romadka, 145 U. S. 29, 12 Sup. Ct. 799; Hoyt v. Horne, 145 U. S. 302, 12 Sup. Ct. 922. The converse is equally true. The patentee may bring the defendant within the letter of his claims, but if the latter has so far changed the principle of the device that the claims of the patent, literally construed, have ceased to represent his actual invention, he is as little subject to be adjudged an infringer as one who has violated the letter of a statute has to be convicted, when he has done nothing in conflict with its spirit and intent. "An infringement," says Mr. Justice Grier in Burr v. Duryee, 1 Wall. 531, 572, "involves substantial identity, whether that identity be described by the terms, 'same principle,' same 'modus operandi,' or any other.

The argument used to show infringement assumes that every combination of devices in a machine which is used to produce the same effect is necessarily an equivalent for any other combination used for the same purpose. This is a flagrant abuse of the term 'equivalent.'"

We have no desire to qualify the repeated expressions of this court to the effect that, where the invention is functional, and the defendant's device differs from that of the patentee* only in form, or in a rearrangement of the same elements of a combination, he would be adjudged an infringer, even if, in certain particulars, his device be an improvement upon that of the patentee. But, after all, even if the patent for a machine be a pioneer, the alleged infringer must have done something more than reach the same result. He must have reached it by substantially the same or similar means, or the rule that the function of a machine cannot be patented is of no practical value. To say that the patentee of a pioneer invention for a new mechanism is entitled to every mechanical device which produces the same ⚫ result is to hold, in other language, that he is entitled to patent his function. Mere variations of form may be disregarded, but the substance of the invention must be there. As was said in Burr v. Duryee, 1 Wall. 531, 573, an infringement "is a copy of the thing described in the specification of the patentee, either without variation, or with such variations as are consistent with its being in substance the same thing. If the invention of the patentee be a machine, it will be infringed by a machine which incorporates in its structure and operation the substance of the invention; that is, by an arrangement of mechanism which performs the same service or produces the same effect in the same way, or substantially the same way. * That two machines produce the same effect will not justify the assertion that they are substantially the same, or that the devices used are therefore mere equivalents for those of the other."

*

Not only is this sound as a general principle of law, but it is peculiarly appropriate to this case. Under the very terms of the first and fourth claims of the Westinghouse patent, the infringing device must not only contain an auxiliary valve, or its mechanical equivalent, but it must contain the elements of the combination, "substantially as set forth." In other words, there must not only be an auxiliary valve, but substantially such a one as is described in the patent, i. e. independent of the triple valve. Not only has the Boyden patent a poppet instead of a slide valve, a matter of minor importance,-but it performs a somewhat different function. In the Westinghouse patent the valve is not in the line of travel between the* auxiliary reservoir and the brake cylinder, and admits train-pipe air only. In the Boyden patent it is in the line of travel, both from the auxiliary reservoir and from the train pipe, and admits both currents of air to the brake cylinder. The by-passage, to which the auxiliary reservoir is merely an adit, is wholly wanting in the Boyden device; both currents of air uniting in chamber, C, and passing to

the brake cylinder together, through the poppet valve.

But a much more radical departure from the Westinghouse patent is found in the partition, 9, separating the valve chamber, C, from the piston chamber, D. This partition has an aperture, B, the capacity of which is less than that of the large passage, A, and intermediate in size between that of the graduating passage, 40, and that of the port covered by the valve, 22. The office of this partition is thus explained by the defendants iL their briefs: When the engineer's valve is thrown wide open, the poppet valve is lifted from its seat by the extreme traverse of the piston, and a new action takes place. "The port of the main valve, 22, is so much larger than the passage, B, that the pressure in the main valve chamber, C, is instantly emptied into the brake cylinder; and as the passage, B, cannot supply air so fast as the mainvalve port can exhaust it, the pressure in the main valve chamber suddenly drops to about five pounds. Meanwhile the passage, A, leading from the auxiliary reservoir to the inner end of the piston chamber, is so much larger than the passage, B, leading from the piston chamber to the main valve chamber, that full reservoir pressure is maintained in the piston chamber between the partition, 9, and the inner side of the piston, thereby holding the piston back firmly at its extreme traverse. But the feed valve, 26, is now exposed on the one side to a train-pipe pressure of about fifty-five pounds, and on the other side to a main valve chamber pressure of only about five pounds; and therefore valve, 26, is instantly forced open by the greater train-pipe pressure, which then vents freely through the said feed valve port into the main valve chamber, C, where it commingles with the auxiliary reservoir air passing through said chamber, and both airs pass together through the port opened by the main valve, 22,*to the brake cylinder. The whole operation is substantially instantaneous, and the result is that the train pipe is freely vented at each car, the time of serially or successively applying the brakes of the several cars from one end of the train to the other is reduced to a minimum, and the train is quickly stopped without shock,—a result which Mr. Westinghouse did not attain with the device of patent No. 360,070, nor did he attain it until he had invented his later apparatus, of patent No. 376,837, not here in suit."

In a word, this partition maintains upon the outside of valve, 26, a much higher pressure than upon the inside, the effect of which is to open feed valve, 26, and admit a full volume of train-pipe air upon the brake cyl inder.

Conceding that the functions of the two devices are practically the same, the means used in accomplishing this function are so different that we find it impossible to say,