with whom concurred Me. Justice Beewee, dissenting.
I am unable to concur in the reasoning and conclusion of the court, and shall briefly state my views. •
The history of the art discloses that the patent in suit.was what is called a “ pioneer invention.”' Jn it, for the .first time, ivas brought to light a method or process which, by the cooperation of the air from the train-pipe with that from the car reservoir, created the “quick action” brake. The'patent,in its specification and claims, clearly described a machine or mechanical combination whereby'the invention was exemplified or rendered operative.
It is not an unwarrantable extension of the term to speak of this invention in suit as a. pioneer, since it is practically conceded in this case, and justly observed by the court below, *574“one of the highest value to the public,” and conspicuously one “ which entitles the proprietor to a liberal protection from the courts in construing the claim.” The very fact that this invention resulted in placing it within the piower of an engineer, running a long train, to stop in about half the time and half the distance within which any similar train had been stopped, is certainly deserving of recognition. The claims of such patents have from time out of mind been allowed a liberal construction, and considered as entitled to the fullest benefit of the doctrine of mechanical equivalents.
It in nowise detracts from the merit of this invention that later devices have been adopted which render its practical operation more efficient. The very term, “ pioneer patent,” signifies that the invention has been followed by others. A pioneer patent does not shut, but opens the door for subsequent invention.
The particular patent in suit was, as I understand it to be admitted, an entire success in supplying passenger trains and short freight trains with a “ quick action ” brake; but while it enabled even the longest freight trains to stop in half the time and half the distance previously occupied, there remained difficulties which required further devices to give to the invention the perfect success which it has now attained.
Being of the character so described as a pioneer, the patent in suit is .entitled to a broad or liberal construction. In other words, the invention is not to be restricted narrowly to the mere details of the mechanism described as a means of carrying the invention into practicable operation.
I cannot assent to what is, perhaps, rather intimated than decided in the opinion of the court that what is called a “process in order to be patentable must involve a chemical or other similar elemental action.” The term “ process ” or “method,” as describing the subject of a patent, is not found in the statutes. No reason is given in the authorities, and I can think of none in the nature of things^ why a new process or method may not be patentable, even though a mechanical device or a mechanical combination may be necessary to render the new process practicable. It seems to be used by the courts *575as descriptive of an invention which, from its novelty and priority in the art to which it belongs, is not to be construed as inhering only in the particular means described, in the letters patent, as sufficient to exemplify the invention and bring it into practical use."
Thus in the case of Winans v. Dormead, 15 How. 330, 341, the patent was.for a new form of the body of a car for the transportation of coal, thus avoiding certain practical difficulties-or disadvantage's in such cars as previously made. To the argument on behalf of the infringer, that the claim of the patent was confined to a single form, and only through and by that form to the principle which it embodies, this court said, per Mr. Justice Curtis:
“ It is generally true that when a patentee describes a machine, and then claims it as described, he is understood to intend to claim, and does by law actually cover, not only the precise form he has described,- but all other forms which embody: his invention ; it being a familiar rule that to copy the principle or mode of- operation described is an ^infringement, although such copy should be totally unlike the original in' form or proportions. . . . It is not sufficient to distinguish this case to say that here the invention consists in % change óf form, and the patentee has claimed one form only. Patent-', able improvements in machinery are almost always made by changing some one or more forms, of one or more parts, and thereby introducing some mechanical principle or mode of action not previously existing in the machine, and so securing a new or improved result. And in the numerous cases in which it has been held that to copy the patentee’s mode of operation was an infringement, the infringer had got forms and proportions not described, and not in terms claimed. If it were not so, no question of infringement could arise. If the machine-, complained of were a copy, in form, of the machine described in the specification, of course, it would be at once seen to be an . infringement. It could be nothing else. It is only ingenious diversities of form and proportion, presenting the appearance of something unlike the thing patented, which give rise to questions.;- and the property of inventors would be valueless *576if it were enough for the defendant to say: Your-improvement consisted in a change of formyou describe and claim but one form; I have not taken that, and so have not infringed.
“The answer is: My infringement did -not consist in a change of form, but in the new employment of principles or powers, in a new mode of operation, embodied in a form by means of which a new or better result is produced; it was this which constituted my invention ; this you have copied, changing only the form. . . . Where form and substance are inseparable it is enough to look at the form only. Where they are separable — where the whole substance of the invention may be copied in a different form, it is the duty of courts and juries to look through the form for the substance of the -invention-— for that which entitled the inventor to his patent, and which the patent was designed to secure; where that is found there is an infringement; and it is not a defence that it is embodied in a form not described and in terms' claimed by the patentee. Patentees sometimes add to their claims an express declaration to the effect that the claim extends to the thing patented, however its form or proportions may be varied. But ■ this is unnecessary. The law so interprets the claim without the addition of these words.”
McCormick v. Talcott, 20 How. 402, 405, was also a case of a mechanical patent, and it was said by Mr. Justice Grier, who delivered the opinion of the court: If the patentee “ be the original inventor of the device or machine, called the divider, he will have a right to treat as inMngers all who make dividers operating on the same principle and performing the same functions by analogous means or. equivalent combination, even though the infringing machine may be an improvement of the original and patentable as such.”
In Morley Sewing Machine Co. v. Lancaster, 129 U. S. 263, there was also a question of an alleged invention of a primary character, and wherein the' invention was embodied in a mechanical combination; and it was held that, in-a pioneer patent,- such as that of Morley, the patentee, the special devices set forth by Morley were not necessary constituents *577of the claims; that his patent was to receive a-liberal construction, in view of the fact that he was a pioneer in the construction of an automatic button sewing machine, arid that his patent was not to be limited to the particular devices or instrumentalities described by him.
In that case extended and approving reference was made to the case of Proctor v. Bennis, 36 Ch. Div. 740, which was a case of an invention embodied in a mechanical contrivance; and the following language of Lord Justice Bowen Avas quoted:
“ Now I think it goes to the root of this case to remember that this is, as Avas described by one of the counsel, really a pioneer, invention, and it is by the light of that, as it seems to me, that Ave ought to consider the question whether there have been variations, or omissions, and additions, which prevent the machine which is complained of from being an infringement of the plaintiff’s. . . . With regard to the additions and omissions,- it is obvious that additions may be an improvement,, and that omissions may be an improvement, but the mere fact that there is an addition, or the mere fact that there is an omission, does not enable you to take the substance of the plaintiff’s patent. The question is not Ayhether the addition is material, or whether the omission is material, but Avhether what has been taken is the substance and essence of. the invention.”
These were cases Avherein the discovery or invention Avas made effective through machines or mechanical combinations, and wherein it was held that the merit of the. process or method was not to be- confined, in the case of a pioneer patent, to the mere form described in the specification as sufficient to make the invention practically operative.
Neilson’s patent, Web. P. C. 275, Avas a noted case, in which the' true distinction Avas drawn between a mere principle, as the subject of a patent, and a process by which a'principle is applied to effect a new and useful result. The Court of Exchequer, in answering the objection that Neilson’s patent Avas for a principle, said:
“ It is very difficult to distinguish it from the specification *578of a patent for a principle, and this at first created in the minds of some of the court much difficulty; but after full consideration, we think the plaintiff does not merely claim a principle, but a machine embodying a principle, and a very . valuable one. We think the case must be considered as .if the principle being well known, the. plaintiff had first-invented a mode of applying it by a mechanical apparatus to furnaces; and his invention consists in this — by interposing a receptacle for heated air between the blowing apparatus and the furnace. In this receptacle he directs the air to be h'eated by the application of heat externally to the receptacle, and thus he accomplishes • the object of applying the - blast, which was before of cold air, in a heated state to the furnace.”
And when the case came before the House of Lords, Lord Campbell said:
“ After the construction first, put upon the patent by the learned judges of the-Exchequer, .' . .. I think the patent must be taken to extend to all machines, of whatever construction, whereby the air is heated intermediately between the blowing apparatus and the blast furnace. That being so, ‘ the learned judge was perfectly justified-in telling the jury that- it was unnecessary for them to compare one apparatus with another, because, confessedly, that S3rstem .of conduit pipes was a mode of heating air by an intermediate vessel between the blowing apparatus and the blast furnace, and, therefore, it was.an infringement of the .patent.” Web. Pat.Cas. 715.
"Very applicable to the present case is the doctrine of Tilghman v. Procter, 102 U. S. 707. It was there held, overruling the case of Mitchell v. Tilghman, 19 Wall. 287, .that, a patent ma3r be validly granted for carrying a principle into effect ; and if the patentee suggests and discovers not only the principle, but suggests and invents how it may be applied to a practical result by • mechanical contrivances and apparatus, and shows that he is aware that no particular sort or. modification of form of apparatus is essential to obtain benefit from the principle, then he may take his patent for. the mode *579of carrying it into effect, and is not under .the necessity of confining himself to one form of apparatus.
Having discussed the previous cases, particularly that of Neilson and of O'Reilly v. Morse, 15 How. 62, Mr. Justice Bradley said:
“‘Whoever discovers that a certain useful result will be produced in any art by the use of certain means is entitled to a patent for it, provided he specifies the means.’ But everything turns on the force and meaning'of the word‘means.’ It is very certain that the means need' not be a machine,- or an apparatus; it may, as the court says, be a process. A machine is a thing. A process is an act, or a mode of acting. The one is visible to the eye —an object .'of perpetual observation. The other is a conception of the mind, seen only by its effects when being executed or performed. Either may be the means of producing a useful result. . . . Perhaps the process is susceptible of be.ing applied in many modes and by the use of many forms of apparatus. The inventor is not bound to describe them all in order to secure to himself the exclusive right to the process, if he is .really its inventor or discoverer. But he must describe.some particular mode, or-some apparatus, by which the process can be applied with at least some beneficial result, in order to show that it is capable of being exhibited and performed in actual experience.”
The Telephone cases, 126 U. S. 1, 532, 533, 535, contain an apt illustration of these principles. Mr. Chief Justice Waite in discussing the case, said :
“ In this art, or, what is the same thing under the patent law, this process, this way of transmitting speech, electricity, one of the forces of nature, is employed ; but electricity, left to itself, will not do what is wanted. The art consists in so controlling the force as to make it accomplish the purpose. It had long been believed that if the vibrations of air caused by the voice in speaking could be reproduced at a distance by means of electricity, the speech •• itself would be reproduced and understood. How to do it was the question. Bell discovered that" it edtdd be dong by gradually changing, the intensity of a continuous electric current, so as to make it *580correspond exactly to the changes in the density of the air caused by the sound of the voice. This was his art. He then devised a way in which these changes of density could be made and speech actually transmitted. Thus his art was put in a condition for practical use. In doing this, both discovery and invention, in the popular sense of those terms, were involved; discovery in finding the art, and invention in devising the means of making it useful. For such discoveries and such inventions the law has given the discoverer and •inventor the right to a patent — -as discoverer, for .the-useful art, process, method of doing a thing he has found; and as inventor, for the means he has devised to make the discovery one of actual value. . . . The patent for the art does not necessarily involve a patent for the particular means employed for using it. Indeed, the mention of any means, in the specification or descriptive portion of the patent, is only necessary to show that the art can be used ; for it is only useful arts — arts which may be used to advantage — that can be made the subject of a patent. The language of the statute is thát ‘ any person who has invented or discovered any new and useful art; machine, manufacture or composition of matter,’ may obtain a patent therefor. Rev. Stat. § 4886. Thus, an art — a process— which is useful, is as much the subject of a patent, as a machine, manufacture or composition of matter. . . . But it is insisted that the claim cannot be sustained, because when the patent was issued Bell had 'not in fact completed his discovery. While it is conceded that he was acting on the right principles, and had adopted the true theory, it is .claimed that the discovery lacked that practical 'development Avhich was necessary to make it patentable. In the language-of counsel, ‘there was still work-to be done, and work calling for the exercise of the utmost ingenuity, and calling for the very highest degree of practical invention.’ It is quite true that when Bell applied for his patent he had never actually transmitted telegraphically spoken words so that they could .be distinctly heard and understood at the receiving end of his line, but in his specification he did describe, accurately and with admirable clearness, his process, that is to say, the *581exact electrical condition that must be created to accomplish his purpose, and- he also described with sufficient precision to enable one of ordinary skill in such matters to make a form of apparatus which, if used in the way pointed out, would produce the required effect, receive the words, and carry them to and deliver them at the appointed place. The particular instrument which he had and which he used in his experiments did not, under- the circumstances in which it was tried, reproduce the words spoken so that they could be clearly' understood, but the proof is abundant and of the most convincing character that other instruments, carefully constructed and made exactly in accordance with the specification, without any additions whatever, have operated and will operate successfully. . . . The law does not require that a discoverer or inventor, in order to get a patent for a process, must have succeeded in bringing his art to the highest degree of perfection. It is enough if he describes his method with sufficient clearness and precision to enable those skilled in the matter to understand what the process is, and if he points out some practicable way of putting it into' operation. , . . Surely a patent for such a discovery is not to be confined to the mere means he improvised to prove the reality of his conception.”
The conclusion justified by the authorities is that whether you'óall Westinghouse’s discovery, that “quick action” may be accomplished by the cooperation of the main pipe air and that from the car reservoir, a process, or a mode of operation, yet if he was the first to disclose it and to describe-a mechanical means to give practical effect to the invention, he must be regarded as a pioneer inventor, and as entitled to protection against those who, availing themselves of the discovery, seek to justify themselves by pointing to mere differences in form in the mechanical devices used.
Much stress was laid in the argument on an alleged disclaimer by the patentee while the application was pending in the Patent Office, whereby it is said Westinghouse must be understood to have abandoned the second claim, or, at any rate, to have consented that that claim should be interpreted *582by the courts as if it contained an auxiliary valve as a material element in the claim.
There are cases, no doubt, in’which it has been held that when a claimant has, under objection in the Patent Office, withdrawn certain claims, or has modified them by adding or striking out terms or phrases, and accepts a patent which does not grant the abandoned or unmodified claims, he cannot be heard to insist upon such a construction of the allowed claims as would cover what had been previously rejected. Shepard v. Carrigan, 116 U. S. 593; Roemer v. Peddie, 132 U. S. 313; Corbin Cabinet Lock Co. v. Eagle Lock Co., 150 U. S. 38.
An examination of.the cited cases, however, will disclose, as I think, that they turned upon matters of construction. In other words, tvere cases where it was questionable what the patent, as actually granted,' meant. In such cases, as in other cases of ambiguity, it may be allowable to consult the application and'file wrapper, and possibly written communications, which may throw light upon claims that are ambiguous or capable of different constructions.
But where the claims allowed are not uncertain or ambiguous, the courts should be slow to permit their construction of a patent, actually granted and delivered, to be affected or controlled by alleged interlocutions between the officers in -the Patent Office and the claimant. No doubt, in proceedings to revoke or cancel a patent granted by inadvertence or by fraudulent representations, it would be competent to show what had taken place in the Patent Office pending the application. But when we consider that often the employes in the Patent Office are inexperienced persons, and that the mass of the business is so vast that it is impossible for the Commissioner or the Chief Examiner to review it, except in a perfunctory way, it can be readily seen how dangerous it would be to modify or invalidate a patent, clear and definite in its terms, by resorting to such uncertain sources of information.
However this may be, I do not perceive that the matters alleged in the present case are entitled to any weight in the construction of the patent. Even if the letter of the claimant’s attorney, written on January 19, 1887, can be looked to *583as helping us to understand the meaning of a patent granted on March 29,1887, it only appears to be an argument as to the meaning or legal effect of the language used in the claims, and does'not amount to a withdrawal or modification of them. .
Accordingly the second claim of the patent is before us •for construction on its own terms, and, to avoid protracting this discussion, the opinion of Judge Morris in the Circuit Court is referred to and adopted as a sound construction of that claim. 66 Fed. Rep. 997. This claim is not, as I read it,- open to the objection that it aims to patent a principle. . It sets forth the discovery that by a cooperation of the air from the auxiliary reservoir and that from the rnain air-pipe, the action of the brakes is quickened and the air vented from the main-air-pipe directly to the brake-cylinder.
But, even if the second claim must, as argued in the'Opinion of the court, be read, by reáson of the letter of the claimant’s attorney, as if it called for the auxiliary valve described in the first and fourth claims,-and .even if, when not so read, it can be regarded as void because simply for a function or principle, nevertheless the- invention, as described in the other claims' and specifications, is clearly set forth, and, under the evidence as to the.state of the art, is entitled to be regarded as a pioneer. Regarding the second claim as a' mere statement’ of the idea or "invention and the other claims as describing a form or combination of mechanism which embodies the invention and renders it operative, all the requisites of the law are sufficiently complied with: .
The only remaining question is that of the infringement, .and that is readily disposed of. For it is conceded in the opinion of the majority of the court that, if the patent in suit is entitled to. a broad construction as a pioneer, embodying a new mode of operation, not limited to the particular means described in. the specification, then the defendant’s “device' is an adoption of the idea or ’ principle'of the Westinghouse patent -with a mechanical equivalent or substitute for the auxiliary valve.
Upon the whole I am of the opinion that .the decree of the *584Circuit Court of Appeals should be reversed and that the cause should be remanded with directions to restore the decree of the Circuit Court.
Mr. Justice Gray and Mr. Justice McKenna also dissented from the opinion and from the decision of the court.