U.S. Supreme Court Westinghouse v. Boyden Power Brake
Co., 170
U.S. 537 (1898) Westinghouse v. Boyden Power Brake
Company Nos. 116, 99 Argued March 10-11,
1898 Decided May 9, 1898 170
U.S. 537 CERTIORARI TO THE CIRCUIT
COURT OF APPEALS FOR THE FOURTH
CIRCUIT Syllabus The Boyden device for a fluid-pressure break is not an
infringement of patent No. 360,070 issued to George Westinghouse,
Jr., March 29, 1887, for a fluid-pressure automatic-brake
mechanism.

															This was a writ of certiorari to review a decree of the circuit
court of appeals reversing a decree of the Circuit Court for the
District of Maryland, which had sustained in part a bill filed by
Westinghouse against the Boyden Power-Brake Company for the
infringement of patent No. 360,070, and from which decree both
parties had taken an appeal to the circuit court of appeals.

															The patent in suit, which was issued March 29, 1887, to George
Westinghouse, Jr., is for a fluid-pressure automatic brake
mechanism, the object of which is said in the specification Page 170 U. S. 538 to be

															"to enable the application of brake shoes to car wheels by fluid
pressure, to be effected with greater rapidity and effectiveness
than heretofore, more particularly in trains of considerable
length, as well as to economize compressed air in the operation of
braking, by utilizing in the brake cylinders the greater portion of
the volume of air which in former practice was directly discharged
into the atmosphere."

															"To this end, my invention, generally stated, consists in a
novel combination of a brake pipe, an auxiliary reservoir, a brake
cylinder, and a triple-valve device, governing, primarily,
communication between the auxiliary reservoir and the brake
cylinder, and secondarily communication directly from the brake
pipe to the brake cylinder."

															There follows here a description of the Westinghouse automatic
brake as theretofore used, its mode of operation, and the defects
or insufficiencies which attended its application to long trains,
in the following language:

															"In the application of the Westinghouse automatic brake, as
heretofore and at present commonly in use, each car is provided
with a main air pipe, an auxiliary reservoir, a brake cylinder, and
a triple valve; the triple valve having three connections, to-wit,
one to the main air-brake pipe, one to the auxiliary reservoir, and
one to the brake cylinder. The main air pipe has a stopcock at or
near each of its ends, to be opened or closed as required, and is
fitted with flexible connections and couplings for connecting the
pipes from car to car of a train so as to form a continuous line
for the transmission of compressed air from a main reservoir
supplied by an air pump on the engine. When the brakes are off or
released, but in readiness for action upon the wheels of the train,
the air which fills the main reservoir and main air pipes has a
pressure of from sixty-five to seventy-five pounds to the square
inch, and by reason of the connections referred to, the same
pressure is exerted in the casings of the triple valves on both
sides of their pistons, and in the auxiliary reservoirs connected
therewith. At the same time, passages called 'release ports' are
open from the brake cylinders to the atmosphere. When it is desired
to apply the brakes, air is Page 170 U. S. 539 allowed to escape from the main air pipes through the engineer's
valve, thereby reducing the pressure in the main air pipes,
whereupon the then higher pressure in the auxiliary reservoirs
moves the pistons of the triple valves, so as to first close the
passages from the triple valves to the brake pipe, and at the same
time close the release ports of all the brake cylinders, and then
open the passages from the auxiliary reservoirs to the brake
cylinders, the pistons of which are forced out by the compressed
air thereby admitted to the brake cylinders, applying the brakes by
means of suitable levers and connections, all of which mechanism is
fully shown in various letters patent granted to me."

															"The application of the brakes with their full force has
heretofore required a discharge of air from the main pipe
sufficient to reduce the pressure in said pipe below that remaining
in the auxiliary reservoir after the brakes have been fully
applied, and it has been found that, while the brakes are
sufficiently quick in action on comparatively short trains, their
action on long trains of from thirty to fifty cars, which are
common in freight service under present practice, is, in a measure,
slow, particularly by reason of the fact that all the air required
to be discharged from the main pipe to set the brakes must travel
from the rear of the train to a single discharge opening on the
engine. This discharge of air at the engine has not only involved a
serious loss of time in braking, but also a waste of air. Under my
present invention, a quicker and more efficient action of the
brakes is obtained, and air which has been heretofore wasted in the
application of the brakes is almost wholly utilized to act upon the
brake pistons."

															After a detailed description of the invention, an important
feature of which is a triple valve (hereinafter more fully
explained in the opinion), with references to the accompanying
drawings, the specification proceeds to state that,

															"so far as the performance of its preliminary function in
ordinary braking is concerned (that is to say, effecting the
closure of communication between the main air pipe and the
auxiliary reservoir, and the opening of communication between the
auxiliary Page 170 U. S. 540 reservoir and the brake cylinder in applying the brakes, and the
reverse operations in releasing the brakes), the triple valve, 10,
accords substantially with that set forth in letters patent of the
United States No. 220,556, granted and issued to me October 14,
1879, and is not therefore saving as to the structural features by
which it performs the further function of effecting the direct
admission of air from the main air pipe to the brake cylinder, as
presently to be described, claimed as of my present invention.
Certain of its elements devised and employed by me prior thereto
will, however, be herein specified in order to render its
construction and operative relation to other members of the brake
mechanism fully intelligible."

															After a further reference to the drawings, he again states
that,

															"so far as hereinbefore described, the triple valve accords in
all substantial particulars with, and is adapted to operate
similarly to, those of my letters patent Nos. 168,359, 172,064, and
220,556; and, in order that it may perform the further functions
requisite in the practice of my present invention, it is provided
with certain additional members, which will now be described."

															These additional members, which are said to be for the purpose
of effecting the admission of air directly from the main air pipe
to the brake cylinder when it is desired to apply the brakes with
great rapidity and full force, consist of (1) a passageway through
which air can be admitted directly from the main air (or train)
pipe to the brake cylinder without passing through the auxiliary
reservoir, and (2) an auxiliary valve in connection with such
passage, that, when the triple-valve piston makes a short or
preliminary movement, the passageway direct from the train-pipe to
brake cylinder, controlled by said valve, will not be opened, while
in the event of a long or full movement of the piston, or "further
traverse," as it is called, such direct passageway will be thrown
wide open to the admission of train-pipe air, and the brake
cylinder will be rapidly filled thereby.

															After describing the auxiliary sliding valve, 41, and its
connections, as well as the operation of the device in ordinary
(nonemergency) cases of checking the speed of or stopping trains,
already fully provided for in previous patents, he proceeds Page 170 U. S. 541 to state its operation in cases of emergency which the patent
was specially designed to cover, as follows:

															"In the event, however, of its becoming necessary to apply the
brakes with great rapidity and with their greatest available force,
the engineer, by means of the valve at his command, instantly
discharges sufficient air from the front end of the main air pipe
to effect a sudden reduction of pressure of about twenty pounds per
square inch therein, whereupon the piston, 12, of the triple valve,
is forced to the extreme limit of its stroke in the direction of
the drain cup, 19, carrying with it the stem, 36, and auxiliary
slide valve, 41, which instantly uncovers the port, 42, and
discharges air from the main air pipe through the opening of the
check valve, 49, and the passages, 46 and 48, to the brake
cylinder; and, each car being provided with one of these devices,
it will be seen that they are successively moved with great
rapidity, there being, practically, on a train of fifty cars, fifty
openings for discharging compressed air from the main pipe, instead
of the single opening heretofore commonly used. Not only is there a
passage of considerable size opened from the brake pipe on each
car, whereby the pressure is more quickly reduced, but the air so
discharged is utilized in the performance of preliminary work, it
being found in practice that the air so taken from the pipe will
exert a pressure of about twenty-five pounds in the brake
cylinders. When the piston, 12, arrives at the extremity of its
stroke as above specified, the supplemental port, 35, of the slide
valve, 14, is brought into communication with the port, 33, and
passages, 22 and 16, which serves to discharge the reservoir
pressure into the brake cylinder, thereby augmenting the pressure
already exerted in the brake cylinder by the air admitted from the
main air pipe. Upon the reduction of the pressure in the main air
pipe below that in the brake cylinders, as by the breaking in two
of the train, the check valve, 49, closes communication between the
passages, 46 and 18, thereby preventing the return of the air from
the brake cylinder to the main air pipe. The feed opening for the
admission of air from the auxiliary reservoir to the brake cylinder
is purposely made of comparatively small diameter, it having been
determined Page 170 U. S. 542 by experiment that the initial application of the brakes should
not be made with maximum force, and this opening may be made of
such size as to apply the brakes exactly in accord with the
requirements of the most efficient work."

															"In using the terms 'triple valve' and 'triple-valve device,' I
refer to a valve device, however specifically constructed, having a
connection with the main air or brake pipe, another with an
auxiliary reservoir or chamber for the storage of power, and
another with a brake cylinder, or its equivalent, for the
utilization of the stored power, and with a release or discharge
passage for releasing the operative power from the brake cylinder,
whether the valves governing these passages or connections are
arranged in one or more cases, and are moved by a piston, or its
equivalent, or by a series of pistons, or their equivalents; there
being numerous examples in the art of constructions varying
materially in appearance, whereby these functions are performed,
both in plenum and vacuum brake mechanisms."

															image:a

															The above drawings are somewhat clearer than those annexed to
the patent, and exhibit the triple valve and its connections in
three positions, viz.: No. 13, released, or "brakes off;" No. 14,
ordinary service application, and No. 16, "quick action"
position.

															The only claims of the patent alleged to have been infringed are
the first, second, and fourth, which read as follows:

															"1. In a brake mechanism, the combination of a main
air-pipe, Page 170 U. S. 543 an auxiliary reservoir, a brake cylinder, a triple valve, and an
auxiliary valve device, actuated by the piston of the triple valve,
and independent of the main valve thereof, for admitting air in the
application of the brake directly from the main air pipe to the
brake cylinder, substantially as set forth."

															"2. In a brake mechanism, the combination of a main air pipe, an
auxiliary reservoir, a brake cylinder, and a triple valve having a
piston whose preliminary traverse admits air from the auxiliary
reservoir to the brake cylinder, and which by a further traverse
admits air directly from the main air pipe to the brake cylinder,
substantially as set forth."

															"4. The combination, in a triple-valve device, of a case or
chest, a piston fixed upon a stem, and working in a chamber
therein, a valve moving with the piston stem, and governing ports
and passages in the case leading to connections with an auxiliary
reservoir and a brake cylinder, and to the atmosphere,
respectively, and an auxiliary valve actuated by the piston stem,
and controlling communication between passages leading to
connections with a main air pipe and with the brake cylinder,
respectively, substantially as set forth."

															The joint and several answer of the Boyden Brake Company and the
individual defendants admitted that such company was engaged in
manufacturing and selling a fluid-pressure brake, but denied that
the same was an infringement upon complainants' patent, and also
denied that Westinghouse was the original inventor of the mechanism
covered by the patent, and alleged that an apparatus substantially
identical in character had been previously granted Westinghouse,
March 5, 1872 (No. 124,404), and that a like apparatus was
previously described in the following patents issued to
Westinghouse, viz.: No. 138,827, May 13, 1873; No. 144,006, October
28, 1873; No. 168,359, October 5, 1875; No. 172,064, January 11,
1876; No. 220,556, October 14, 1879,-and also in three patents to
other parties, not necessary here to be specifically mentioned.

															The answer further denied any infringement of the first, fourth,
and fifth claims of the patent sued upon (No. 360,070), and, with
respect to the second claim, averred the same to be Page 170 U. S. 544 invalid because the combination of parts therein named is
inoperative to perform, and incapable of performing, the function
set forth in said claim, and that, if the said claim be considered
merely as the combination of parts therein set forth, and without
reference to the function described as performed by it, it is
invalid for the reason that the same combination of parts is shown
in most of the prior patents above cited, and has been publicly
used by the complainants for a long time prior to the date of the
said letters patent No. 360,370.

															The answer further averred the claim to be uncertain and
ambiguous, and, if the functions recited by it are construed as
amplifying the description of the combination to distinguish this
combination from that shown in the prior patents,

															"then the defendants say that the said claim is anticipated by
the prior letters patent issued to George A. Boyden on June 26,
1883, for the reason that air-brake valves made in accordance with
the last-mentioned patent embody the same combination of parts, and
will perform the same functions, and operate in substantially the
same manner, as stated in said second claim."

															Upon a hearing in the circuit court upon the pleadings and
proofs, that court was of opinion that the second claim was valid,
and had been infringed, but that defendants had not infringed
claims 1 and 4, and as to those the bill was dismissed. 66 F. 997.
From the decree entered in pursuance of this opinion, both parties
appealed to the Court of Appeals for the Fourth Circuit, which
affirmed the action of the circuit court with respect to the first
and fourth claims, but reversed it with respect to the second
claim, and dismissed the bill. 70 F. 816. Whereupon complainants
applied for, and were granted, a writ of certiorari.

															Full copies the principal Westinghouse patents are printed in Westinghouse Air-Brake Co v. New York Air-Brake Co., 63 F.
962, and of the Boyden patents in the report of this case in 73 F.
816. Page 170 U. S. 545 MR. JUSTICE BROWN, after stating the facts in the foregoing
language, delivered the opinion of the court.

															The history of arresting the speed of railway trains by the
application of compressed air is one (to which the records of the
Patent Office bear frequent witness) of a gradual progress from
rude and imperfect beginnings, step by step, to a final
consummation, which, in respect to this invention, had not been
reached when the patent in suit was taken out, and which, it is
quite possible, has not been reached to this day. It is not
disputed that the most important steps in this direction have been
taken by Westinghouse himself.

															The original substitution of the air brake for the old hand
brake was itself almost a revolution, but the main difficulty seems
to have arisen in the subsequent extension of that system to long
trains of freight cars, in securing a simultaneous application of
brakes to each of perhaps forty of fifty cars in such a train, and
finally in bringing about the instantaneous as well as simultaneous
application of such brakes in cases of emergency, when the
speediest possible stoppage of the train is desired to avoid a
catastrophe.

															Patent No. 88,929, issued April 13, 1869, appears to have been
the earliest of the Westinghouse series. This brake, known as the
"straight air brake," consisted of an air-compressing pump,
operated by steam from the locomotive boiler, by which air was
compressed into a reservoir, located under the locomotive, to a
pressure of about 80 pounds to the square inch. This reservoir,
being still in use, is now known as the "main reservoir." From this
reservoir an air pipe, usually called the "train-pipe," led into
the cab, where the supply of air was regulated by an "engineer's
valve," and thence down and back under the tender and cars, being
united between the cars by a flexible hose with metal couplings,
rendering the train-pipe continuous. These couplings were
automatically Page 170 U. S. 546 detachable -- that is, while they kept their grip upon each
other under the ordinary strains incident to the running of the
train, they would readily pull apart under unusual strains, as when
the car coupling broke and the train pulled in two.

															From the train-pipe of each car a branch pipe connected with the
forward end of a cylinder called the "brake cylinder," which
contained a piston, the stem of which was connected with the brake
levers of the car. This piston was moved and the brakes applied by
means of compressed air admitted, through the train-pipe and its
branches, into the forward end of the brake cylinder. When the
brakes were to be applied, the engineer opened his valve, and
admitted the compressed air into the train-pipes and brake
cylinders, whereby the levers were operated and the brakes applied.
To release the brakes, he reversed the valve, whereby the
compressed air escaped from the brake cylinders, and flowed forward
along the train-pipe to the escape port of the engineer's valve,
and thence into the atmosphere. Upon the release of the compressed
air, the pistons of the brake cylinders were forced forward again
by means of springs, and the brake shoes removed from the wheels.
By means of this apparatus, the train might be wholly stopped or
slowed down by a full or partial application of the brakes. As
between a full stop and a partial stop, or slow speed, there was
only a question of the amount of air to be released from the main
reservoir. The validity of this patent was sustained by the Circuit
Court for the Northern District of Ohio (Mr. Justice Swayne and
Judge Welker sitting) in Westinghouse v. Air-Brake Co., 9
Official Gazette 538. The court said in its opinion that while
Westinghouse was not the first to conceive the idea of operating
railway brakes by air pressure, such fact did not detract at all
from his merits or rights as a successful inventor; that the new
elements introduced by him "fully substantiated his pretensions as
an original and meritorious inventor, and entitled him, as such, to
the amplest protection of the law," and that it appeared from the
record and briefs that he was the first to put an air brake into
successful actual use.

															While the application of this brake to short trains was Page 170 U. S. 547 reasonably successful, the time required for the air to pass
from the locomotive to the rear cars of a long train (about one
second per car) rendered it impossible to stop the train which the
requisite celerity, since in a train of ten cars it would be ten
seconds before the brakes could be applied to the rear car, and to
a freight train of fifty cars nearly a minute. While the speed of
the foremost car would be checked at once, those in the rear would
proceed at unabated speed and, in their sudden contact with the
forward cars, would produce such shocks as to often cause damage.
As a train moving at the rate of fifty miles an hour makes over
seventy feet per second, a train of fifty cars would run half a
mile before the brakes could be applied to the rear car. So too, if
the rear end of the train became detached from the forward end by
the rupture of the train-pipe or couplings, the brakes could not be
applied at all, since the compressed air admitted to the train-pipe
by opening the engineer's valve would escape into the atmosphere
without operating the brakes, or, if the brakes were already
applied, they would be instantly released when such rupture
occurred.

															The first step taken towards the removal of these defects
resulted in what is known as the "automatic brake," described first
in patent No. 124,404 in a crude form, and, after several
improvements, finally culminating in patent No. 220,556 of 1880.
The salient features of this brake were an auxiliary reservoir
beneath each car for the reception and storage of compressed air
from the main reservoir, and a triple valve, so called,
automatically controlling the flow of compressed air in three
directions, by opening and closing at the proper times, three ports
or valve openings, viz.: 1. a port or valve, known as the
"feeding-in valve," from the train-pipe to the auxiliary reservoir,
allowing the auxiliary reservoir to fill so as to be ready when the
brakes were applied, 2. a port or valve from the auxiliary
reservoir to the brake cylinder, which allowed a flow of compressed
air to apply the brakes, and was called the "main valve," 3. a port
or valve from the brake cylinder to the open air, denominated the
"release valve," to be opened when it was desired to release the
brakes. Page 170 U. S. 548 The operation of these valves was as follows: before the train
starts, compressed air from the main reservoir is permitted to flow
back through the train-pipe, and through valve No. 1, for the
purpose of charging the auxiliary reservoir beneath each car with a
full working pressure of air. When it is desired to apply the
brakes, the engineer's valve is shifted, and the air in the
train-pipe is allowed to escape into the atmosphere at the engine.
Thereupon the compressed air in the auxiliary reservoir closes
valve No. 1, leading to the train-pipe, and opens the main valve,
No. 2, from the auxiliary reservoir to the brake cylinder, whereby
the piston of that cylinder operates upon the brake levers and
applies the brakes. By this use of the auxiliary reservoirs, a
practically simultaneous application of the brakes is secured for
each car. This application of the brakes is secured, not by direct
application of compressed air from the engine through the
train-pipe, but by a reverse action, whereby the air is allowed to
escape from the train-pipe towards the engine, the pressure being
applied by the air escaping from the auxiliary reservoirs. It also
results that, if a train should pull in two, or a car become
detached, the same escape of air occurs, the same action takes
place automatically at the broken part, and the same result follows
by the escape of the compressed air through the separated
couplings. When it is desired to release the brakes, the engineer's
valve is again shifted, and the compressed air not only opens valve
No. 1, from the train-pipe to the auxiliary reservoir, but valve
No. 3, from the brake cylinder to the open air, which allows the
air from the brake cylinder to escape, and thus release the
brake.

															From this description it will be seen that the action of the
automatic brake was in fact the converse of the straight air brake,
and that the result was to obviate the most serious defects which
had attended the employment of the former.

															This automatic brake appears, in its perfected form, in patent
No. 220,556, although this patent was but the culmination of a
series of experiments, each successive step in which appears in the
prior patents. Thus, in patent No. 124,404 (1872) Page 170 U. S. 549 is introduced the auxiliary reservoir beneath each car, in
connection with a double line of brake pipes and a single cock,
with suitable ports for charging the reservoir and for operating
the brakes -- a device which was obviously the foundation of the
triple valve which first made its appearance in patent No. 141,685
(1873), in which the main valve, which admitted air from the
auxiliary reservoir to the brake cylinder, was of the poppet form,
and, as a poppet valve can govern only one port, separate valves
had to be provided for feeding in the air from the train-pipe to
the auxiliary reservoir, and for discharging the air from the brake
cylinder to release the brakes. In subsequent patents, No. 144,006
(1873) and No. 163,242 (issued in 1875 to C. H. Perkins, and
assigned to Westinghouse), Mr. Westinghouse improved upon his prior
devices by substituting a sliding-piston valve for the poppet form
of main valve previously used by him. This enabled the piston to
perform the feed-valve function of admitting air from the
train-pipe to the auxiliary reservoir, the main-valve function of
admitting air from the auxiliary reservoir to the brake cylinder to
apply the brakes, and the release-valve function of discharging the
air from the cylinder to release the brakes. In patent No. 168,359
(1875) a piston actuating a slide valve was substituted for the
piston valve, and after a series of experiments, which did not seem
to have been successful, he introduced into patent No. 217,828 the
idea of venting the train-pipe not only at the locomotive, but also
under each car, in order to quicken the application of the brakes.
Prior to this time,

															"when the engineer desired to apply his brakes with full force,
he operated the valve at the engine and opened the port wide,
letting the compressed air out of the train-pipe at the locomotive,
then its only vent. The air, as before said, had to travel from the
rear cars along the cars forward to the engine before it could
lessen the pressure of the train-pipe air, . . . and before the
brake cylinder could be operated with air from the auxiliary
reservoirs. In a train of fifty cars, it would have to travel
nearly half a mile to get out at the engine."

															He embodied in patent No. 220,556 (1879) the most complete form
of the automatic brake. As stated by the Page 170 U. S. 550 court below, the ordinary work of braking was performed by a
partial traverse of its chamber by the triple-valve piston,
graduated, according to the purpose desired at the will of the
engineer, and emergency work was done by an extreme traverse of the
piston to the end of its chamber.

															While the automatic brake had thus obviated the most important
defects of the old or straight air brake, and came into general use
upon passenger trains throughout the country, it was found, in
practice, upon long freight trains, that the air from the auxiliary
reservoirs did not act with sufficient promptness upon the brakes
of the rear cars, where a particularly speedy action was required,
and that it would be necessary to devise some other means for cases
of special emergency. In the business of transporting freight over
long distances, the tendency has been in the direction of
increasing the load by using stronger and heavier cars and larger
locomotives. Upon a long train of this kind, composed of thirty to
fifty cars, a demand was made for quicker action in cases of
emergency than had yet been contemplated, although, for ordinary
work, such as checking the speed of a train while running, holding
it at a slow speed on a down grade, and also for making the
ordinary station stops, the automatic brake was still sufficient,
and produced satisfactory results, even in the equipment of long
and heavy trains. But, however effective for ordinary purposes, the
automatic brake did not sufficiently provide for certain
emergencies, requiring prompt action, and therefore failed in a
single important particular.

															Upon examination of these defects, it was found that they could
only be remedied by securing (1), in cases of emergency, a more
abundant discharge of compressed air into the brake cylinder, and
(2) an escape of air near to each triple valve without requiring
the escaping air to travel all the way back to the engine. The
latter device having been already embodied in patent No. 217,838,
these features Mr. Westinghouse introduced into the patent in suit,
by which a passage was opened directly from the train-pipe, filled
from the main reservoir on the engine, to the brake cylinder,
through which, in cases of emergency, the train-pipe air, instead
of being discharged Page 170 U. S. 551 into the atmosphere, could pour directly from the train-pipe
into the brake cylinder. This operation resulted in charging the
brake cylinder and applying the brakes more quickly than before,
and also, by reason of the fact that the filling of the brake
cylinder from the train-pipe on one car made what was, in effect, a
local vent for the release of pressure sufficient to operate the
valve on the next car behind, each successive valve operated more
quickly than when a diminution of pressure was caused by an escape
of air only at the locomotive. The direct passage of the air from
the train-pipe to the brake cylinder was effected by a valve, 41,
colored red in the above diagrams, which is never opened except in
cases of emergency. In ordinary cases, when the brakes are desired
to be applied, sufficient air is released from the train-pipe to
open the passage from the auxiliary reservoir to the brake cylinder
by what is called a "preliminary traverse" of the piston, 12; but,
when a quick action is required, sufficient air is drawn from the
train-pipe not only to open this passage, but, by a further
traverse of the piston, to shove valve 41 off its port, and
introduced air directly from the train-pipe to the brake cylinder,
as shown in the third drawing above set forth.

															image:b

															In the foregoing skeleton drawings, from which all details of
construction and all figures of reference not necessary for a clear
understanding of the structure are omitted, the Page 170 U. S. 552 essential parts are colored, so that their changes of position
in the different stages of action can be easily followed.

															The access of train-pipe air is shown located at the right end
of the structure, instead of the left, as in the patent drawings,
simply for greater clearness. Its course from the train-pipe to the
auxiliary cylinder is through the small port above the upper arm of
the piston, 12.

															The main valve of the triple is black. Its office is to
admit auxiliary reservoir air to brake cylinder.

															The quick action valve is colored red. Its office is to
admit train-pipe air to brake cylinder.

															The release port is colored green. Its office it to
discharge air from brake cylinder, in releasing the brakes.

															There is also shown, in yellow, what is known as the
"graduating valve," the function of which will be hereafter
explained. As at present used, the triple valve is in reality a
quadruple valve.

															The flow or movement of air in the several positions of the
structure is also shown by colored lines and arrows, viz.: Air released from brake cylinder to open air by green arrow.

															Air flowing from auxiliary reservoir to brake cylinder, in
"service" application of the brakes, by red line, and air
flowing from train-pipe to brake cylinder in "quick action"
application, by blue line.

															This patent, although it introduced a novel feature into the
art, does not seem to have been entirely successful in its
practical operation, since in October of the same year, an
improvement was patented, No. 376,837, with the object of still
further increasing the rapidity of action. As observed by the
district judge in this connection,

															"the success of this improved device, No. 376,837, has
demonstrated that the invention, by which the further traverse of
the triple-valve piston beyond the extent of the traverse required
for the ordinary application of the brakes is made to admit a large
volume of train-pipe air directly to the brake cylinder, was one of
great importance. The proofs show that a quick action automatic
brake, which would give the results which this brake has
accomplished, was eagerly Page 170 U. S. 553 sought after by inventors and car builders, and all had failed
until Westinghouse discovered that it could be done by this mode of
operation."

															We are now in position to take up the several claims of the
patent in suit, and their defenses thereto. It may be stated
generally that the position of complainants in this connection is
that the novel feature of this patent, in respect to which they are
entitled to be protected, is the opening of a passage directly from
the train-pipe to the brake cylinder, without passing through the
auxiliary reservoir and without reference to the means by which
such passageway is controlled. Defendants' theory is that they are
limited to such passageway when governed by the auxiliary valve,
41, a device which, although of no utility as arranged in the
patent in suit, became afterwards exceedingly useful when further
combined with the supplementary piston shown in patent No. 376,837.
The further inference is that, as they do not use the auxiliary
valve of this patent, they cannot be held liable as infringers.

															Complainants' case must rest either upon the theory that the
admission of compressed air directly from the train-pipe to the
brake cylinder is patentable as a function or that the means
employed by the defendants for that purpose are a mechanical
equivalent for the auxiliary valve, 41, described in the
patent.

															1. The first theory is based upon the second claim, which
is:

															"In a brake mechanism, the combination of a main air pipe, an
auxiliary reservoir, a brake cylinder, and a triple valve, having a
piston, whose preliminary traverse admits air from the auxiliary
reservoir to the brake cylinder, and which, by a further traverse,
admits air directly from the main air pipe to the brake cylinder,
substantially as set forth."

															In the construction of this claim, the district judge was of
opinion that it was broad enough to cover other devices in which
air was admitted directly from the train-pipe to the brake cylinder
by the further traverse of the piston actuating a valve admitting
such air, and that the defendants could not exculpate themselves
from the charge of infringement from the fact that, in their
device, the train-pipe air was admitted Page 170 U. S. 554 through the triple-valve chamber, and not through a by-passage,
nor by the fact that in their device the further traverse of the
piston opens the main valve in a special manner which produces the
same result, but does not make use of a separate auxiliary
valve.

															Upon the other hand, the circuit court of appeals held that "the
transmission of train-pipe air and auxiliary reservoir air
simultaneously to the brake cylinder is a result of [or] function,
and is not patentable;" that

															"the means by which this or any other result or function is
accomplished may be many and various, and if these several means
are not mechanical equivalents, each of them is patentable."

															It was of opinion that when the second claim,

															"in its language describing the action of that device, failed to
describe any means by which the extreme traverse of the piston
produced it, declaring merely that the piston, 'by a further
traverse, admits air directly from the main air pipe to the brake
cylinder,' it was fatally defective; claiming only a result, which
is public property, and not identifying the specific means (his own
property) by which the result is achieved."

															It is true, as observed by the court of appeals, that the
further traverse of the piston for use in cases of emergency had
been shown in prior patents, but it had never been employed for the
purpose of admitting air directly from the main air pipe to the
brake cylinder until the patent in suit was taken out.

															The claim in question is, to a certain extent, for a function, viz., the admission of air directly from the train-pipe to
the brake cylinder, and is only limited to such function when
performed by the further traverse of the piston of the triple
valve. This limitation, however, does not obviate the objection
that the means are not fully and specifically set forth for the
performance of the function in question.

															The difficulty we have found with this claim is this, that if it
be interpreted simply as a claim for the function of admitting air
to the brake cylinder directly from the train-pipe, it is open to
the objection (held in several cases to be fatal) that the mere
function of a machine cannot be patented. Page 170 U. S. 555 This rule was clearly laid down in the leading case of Corning v.
Burden , 15 How. 252, in which Mr. Justice Grier,
delivering the opinion of the Court, drew the distinction between
such processes as were the result or effect of "chemical action, by
the operation or application of some element or power of nature, or
of one substance to another," and the mere result of the operation
of a machine, with regard to which he says:

															"It is for the discovery or invention of some practicable method
or means of producing a beneficial result or effect that a patent
is granted, and not for the result or effect itself. It is when the
term 'process' is used to represent the means or method of
producing a result that it is patentable, and it will include all
methods or means which are not effected by mechanism or mechanical
combinations."

															"But the term 'process' is often used in a more vague sense, in
which it cannot be the subject of a patent. Thus we say that a
board is undergoing the process of being planed; grain, of being
ground; iron, of being hammered or rolled. Here, the term is used
subjectively or passively, as applied to the material operated on,
and not to the method or mode of producing that operation, which is
by mechanical means, or the use of a machine, as distinguished from
a process."

															"In this use of the term, it represents the function of a
machine, or the effect produced by it on the material subjected to
the action of the machine. But it is well settled that a man cannot
have a patent for the function or abstract effect of a machine, but
only for the machine which produces it."

															In the subsequent case of Burr v.
Duryee , 1 Wall. 531, 68 U. S. 570 ,
Mr. Justice Grier laid down the same principle, as follows:

															"The patent act grants a monopoly to anyone who may have
discovered or invented any new and useful art, machine,
manufacture, or composition of matter. . . . The law requires that
the specification"

															"should set forth the principle and the several modes in which
he has contemplated the application of that principle, or character
by which it may be distinguished from other inventions, and shall
particularly point out the part, improvement, or combination which
he claims as Page 170 U. S. 556 his own invention or discovery."

															"We find here no authority to grant a patent for a 'principle,'
or a mode of operation, or an idea, or any other
abstraction. A machine is a concrete thing, consisting of parts or
of certain devices and combination of devices. The principle of a
machine is properly defined to be its mode of operation, or that
peculiar combination of devices which distinguish it from other
machines. A machine is not a principle or an idea. The use of ill
defined, abstract phraseology is the frequent source or error. It
requires no great ingenuity to mystify a subject by the use of
abstract terms of indefinite or equivocal meaning. Because the law
requires a patentee to explain the mode of operation of his
peculiar machine which distinguishes it from others, it does not
authorize a patent for a 'mode of operation as exhibited in the
machine.' Much less can any inference be drawn from the statute
that an inventor who has made an improvement in a machine, and thus
effects the desired result in a better or cheaper manner than
before, can include all previous inventions, and have a claim to
the whole art, discovery, or machine which he has improved. All
others have an equal right to make improved machines, provided they
do not embody the same, or substantially the same, devices, or
combination of devices, which constitute the peculiar
characteristics of the previous invention."

															So, also, in Fuller v. Yentzer, 94 U. S.
288 , this Court, speaking through Mr. Justice Clifford,
also said:

															"Patents for a machine will not be sustained if the claim is for
a result, the established rule being that the invention, if any
within the meaning of the patent act, consists in the means or
apparatus by which the result is obtained, and not merely in the
mode of operation, independent of the mechanical devices employed.
Nor will a patent be held valid for a principle or for an idea, or
any other mere abstraction."

															Most or the prior authorities upon this subject are reviewed in
the recent case of Locomotive Works v. Medart, 158 U. S. 68 , in
which it was also held that a valid patent could not be obtained
for a process which involved nothing more than the operation of a
piece of mechanism, or the function Page 170 U. S. 557 of a machine. See also, to the same effect, Wicke
v. Ostrum, 103 U. S. 461 , 103 U. S. 469 .
These cases assume, although they do not expressly decide, that a
process, to be patentable, must involve a chemical or other similar
elemental action, and it may be still regarded as an open question
whether the patentability of processes extends beyond this class of
inventions. Where the process is simply the function or operative
effect of a machine, the above cases are conclusive against its
patentability; but where it is one which, though ordinarily and
most successfully performed by machinery, may also be performed by
simple manipulation -- such, for instance, as the folding of a
paper in a peculiar way for the manufacture of paper bags, or a new
method of weaving a hammock -- there are cases to the effect that
such a process is patentable though none of the powers of nature be
invoked to aid in producing the result. Eastern Paper Bag Co.
v. Standard Paper Bag Co., 30 F. 63; Union Paper Bag
Machine Co. v. Waterbury, 39 F. 389; Travers v. Am.
Cordage Co., 64 F. 771. This case, however, does not call for
an expression of our opinion upon this point, nor even upon the
question whether the function of admitting air directly from the
train-pipe to the brake cylinder be patentable or not, since there
is no claim made for an independent process in this patent, and the
whole theory of the specification and claims is based upon the
novelty of the mechanism.

															But if the second claim be not susceptible of the interpretation
that it is simply for a function, then the performance of that
function must be limited to the particular means described in the
specification for the admission of air from the train-pipe to the
brake cylinder. This we understand to be the theory of the
defendants, and this raises the same question which is raised under
the first and fourth claims -- whether defendants' device contains
the auxiliary valve of the Westinghouse patent, or its mechanical
equivalent.

															In this view, it becomes unnecessary to express an opinion
whether the second claim be valid or not, since, in the aspect of
the case most favorable to the complainants, it is necessary to
read into it something which is not found there, or, in the Page 170 U. S. 558 language of complainants' brief,

															"to refer back to the specification -- not, it is true, for a
slavish adoption of the identical instrumentalities therein
described, but for the understanding of the essential and
substantial features of the means therein illustrated."

															In thus reading the specification into the claim, we can adopt
no other construction than to consider it as if the auxiliary valve
were inserted in the claim in so many words, and then to inquire
whether the defendants make use of such valve, or its mechanical
equivalent.

															There are two other facts which have a strong bearing in the
same connection and preclude the idea that this can be interpreted
as a claim for a function without reading into it the particular
device described in the specification.

															One of these is that the claim is for a triple-valve device,
etc., for admitting air from the main air pipe to the brake
cylinder, "substantially as set forth." These words have been
uniformly held by us to import into the claim the particulars of
the specification, or, as was said in Seymour v.
Osborne , 11 Wall. 516, 78 U. S.
547 :

															"Where the claim immediately follows the description of the
invention, it may be construed in connection with the explanations
contained in the specifications, and where it contains words
referring back to the specifications, it cannot be properly
construed in any other way."

															In that case, it was held that a claim which might otherwise be
bad as covering a function or result, when containing the words
"substantially as described" should be construed in connection with
the specification, and, when so construed, was held to be valid. To
the same effect is the Corn-Planter
Patent , 23 Wall. 181, 90 U. S.
218 .

															Again, it appears from the file wrapper and contents that in his
original application, Mr. Westinghouse made a broad claim for the
admission of air directly from the main air pipe to the brake
cylinder, which was rejected upon reference to a prior patent to
Boyden, No. 280,285, and that on January 19, 1887, his attorney
wrote the Patent Office in the following terms:

															"It is respectfully submitted that while the Boyden patent, No.
280,285, referred to, shows that what the inventor terms Page 170 U. S. 559 'an always-open one-way passage,' by which communication may be
established under certain conditions between the main air pipe or
train-pipe, and hence might be held to meet the terms of the claim
as originally broadly drawn, yet it fails to embody a device which
in structure or function corresponds with the auxiliary valve of
applicant, which in no sense relates to 'an always-open one-way
passage.' This amended claim, above submitted, prescribes a valve
device, actuated by the piston of the triple valve, for admitting
air to the brake cylinder in the application of the brake, while
Boyden's check valve, d, is not actuated by the piston,
and is designed to recharge the auxiliary reservoir and brake
cylinder while the brakes are on. It is submitted as to claim 2
that a piston, which by its preliminary traverse admits air from
the auxiliary reservoir to the brake cylinder and by its further
traverse admits air directly from the main air pipe to the brake
cylinder, as set forth in said claim, is not found in the Boyden
patent, the check valve, d, of which is described as
actuated by the manipulation of the cock, q, on the
locomotive, to 'recharge and continue charging the reservoir and
brake cylinder while the brakes are applied.' . . . It is to be
understood that applicant does not seek to broadly claim a
device for admitting air directly from the main air pipe to the
brake cylinder, as the four-way cock long heretofore employed
by him (similar to the cock, K, of the Boyden patent) would be a
structure of such character. When, however, the triple valve is
provided with an auxiliary valve, operated by its piston, which
performs a new function additional to that of the triple valve
as previously employed, it is believed that such combination is wholly novel."

															So, too, in the specification, it is stated:

															"So far as the performance of its preliminary function in
ordinary braking is concerned -- that is to say, effecting the
closure of communication between the main air pipe and the
auxiliary reservoir and the opening of communication between the
auxiliary reservoir and the brake cylinder in applying the brakes,
and the reverse operations in releasing the brakes -- the triple
valve, 10, accords substantially with that set forth in letters
patent of the United States No. 220,556, granted and Page 170 U. S. 560 issued to me October 14, 1879, and is not therefore saving as to
the structural features by which it performs the further
function of effecting the direct admission of air from the main air
pipe to the brake cylinder, as presently to be described, claimed
as of my present invention."

															Apparently, too, in consequence of the above letter of January
19, 1887, the patentee erased from his original specification the
following sentence:

															"Further, while, in the specific construction described and
shown, the function of admitting air from the main pipe is
performed by a valve separate from that which effects the
preliminary admission of reservoir pressure to the cylinder, a
modification in which the same office is performed by a valve
integral with the main valve and formed by an extension thereof
would be included in and embody the essential operative features of
my invention,"

															and inserted in its place the following:

															"I am aware that a construction in which 'an always-open one-way
passage' from the main air pipe to the brake cylinder is uncovered
by the piston of the triple valve simultaneously with the opening
of the passage from the auxiliary reservoir to the brake cylinder
has been heretofore proposed, and such construction, which involves
an operation different from that of my invention, I therefore
hereby disclaim."

															We agree with the defendant that this correspondence, and the
specification as so amended, should be construed as reading the
auxiliary valve into the claim, and as repelling the idea that this
claim should be construed as one for a method or process. Language
more explicit upon this subject could hardly have been
employed.

															While it is true that no claim is formally made for the
admission of train-pipe air directly to the brake cylinder as a
method or process, a construction is given by the complainants and
the circuit court to the second claim which eliminates the
mechanical features described, and one which could only be
supported upon the theory that the claim was for a method or
process. If the mechanism described by Westinghouse, and
particularly the auxiliary valve, be not essential to the validity
of the second claim, then it could only be supported Page 170 U. S. 561 upon the theory that it was for the process of admitting
train-pipe air directly to the brake cylinder.

															2. The first and fourth claims of this patent are as
follows:

															"1. In a brake mechanism, the combination of a main air pipe, an
auxiliary reservoir, a brake cylinder, a triple valve, and an
auxiliary valve device, actuated by the piston of the triple valve,
and independent of the main valve thereof, for admitting air in the
application of the brake directly from the main air pipe to the
brake cylinder, substantially as set forth."

															"4. The combination, in a triple-valve device, of a case or
chest, a piston fixed upon a stem and working in a chamber therein,
a valve moving with the piston stem, and governing ports and
passages in the case leading to connections with an auxiliary
reservoir and a brake cylinder and to the atmosphere, respectively,
and an auxiliary valve actuated by the piston stem and controlling
communication between passages leading to connections with a main
air pipe and with the brake cylinder, respectively, substantially
as set forth."

															These two claims are practically little more than different
expressions of one and the same invention. In both of them, there
is a main air pipe, an auxiliary reservoir, a brake cylinder, a
triple valve and piston, described in the fourth claim as "fixed
upon a stem and working in a chamber" in a case or chest, and an
auxiliary valve, and in the fourth claim, also, a case or chest,
which contains the whole device, and is immaterial.

															In both of these claims, an auxiliary valve is named as an
element. In the first, it is described as "actuated by the piston
of the triple valve, and independent of the main valve thereof,"
and in the fourth as "actuated by the piston stem, and controlling
communication between passages leading to connections with the main
air pipe and with the brake cylinder."

															To what liberality of construction these claims are entitled
depends, to a certain extent, upon the character of the invention
and whether it is what is termed, in ordinary parlance, a
"pioneer." This word, although used somewhat loosely, is commonly
understood to denote a patent covering a function Page 170 U. S. 562 never before performed, a wholly novel device, or one of such
novelty and importance as to mark a distinct step in the progress
of the art, as distinguished from a mere improvement or perfection
of what had gone before. Most conspicuous examples of such patents
are the one to Howe, of the sewing machine; to Morse, of the
electrical telegraph, and to Bell, of the telephone. The record in
this case would indicate that the same honorable appellation might
be safely bestowed upon the original air brake of Westinghouse, and
perhaps also upon his automatic brake. In view of the fact that the
invention in this case was never put into successful operation, and
was to a limited extent anticipated by the Boyden patent of 1883,
it is perhaps an unwarrantable extension of the term to speak of it
as a "pioneer," although the principle involved subsequently, and
through improvements upon this invention, became one of great value
to the public. The fact that this invention was first in the line
of those which resulted in placing it within the power of an
engineer, running a long train, to stop in about half the time and
half the distance within which any similar train had stopped, is
certainly deserving of recognition, and entitles the patent to a
liberality of construction which would not be accorded to an
ordinary improvement upon prior devices. At the same time, as
hereinafter observed, this liberality must be exercised in
subordination to the general principle above stated -- that the
function of a machine cannot be patented, and hence that the fact
that the defendants' machine performs the same function is not
conclusive that it is an infringement.

															The device made use of by the defendants is exhibited in patents
No. 481,134 and No. 481,135, both dated August 16, 1892, and both
of which were granted after the commencement of this suit. There
are two forms of this patent, one of which, illustrated in patent
No. 481,135, is here given in its three positions -- of
release(20), service application (21), and quick action (22).

															In this device there is found a main air pipe, an auxiliary
reservoir, a brake cylinder, a triple, or rather, a quadruple,
valve and piston, 29, with three ports -- first, for the
admission Page 170 U. S. 563 image:c

															of air from the train-pipe to the brake cylinder through the
feeding-in valve, 26; second, for the passage of air from the
auxiliary reservoir to the brake cylinder through the apertures, i, j, k, in the stem slide valve, 18; and, third, for the
release of air from the brake cylinder to the exhaust port by means
of valve, 17, colored green. Whether this device has an auxiliary
valve or not is one of the main questions in the case,
complainants' theory being that poppet valve, 22, is an auxiliary
valve, while defendants' claim is that it is in reality the main
valve.

															image:d

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

															The auxiliary reservoirs are charged by air under pressure, Page 170 U. S. 564 entering from the train-pipe, raising and passing through the
feeding-in value 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
value, and the reduction of pressure on the right side of the
piston, 29, causes in 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
quick action 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 Page 170 U. S. 565 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 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, e, 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 value
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 value," 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 Page 170 U. S. 566 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, i, 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 value) is, in ordinary
cases, performed principally, if not 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 value, 22, which has
also been lifted from its seat by the further traverse of the
piston.

															One of the main 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 Page 170 U. S. 567 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 , 101 U. S. 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 train-pipe 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 Page 170 U. S. 568 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 ; Morey v.
Lockwood , 8 Wall. 230; Elizabeth v. Pavement
Company, 97 U. S. 137 ; Sessions v. Romadka, 145 U. S. 29 ; Hoyt v. Horne, 145 U. S. 302 . 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, 68 U. S.
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 Page 170 U. S. 569 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, 68 U. S. 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 Page 170 U. S. 570 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 in 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 main valve 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, Page 170 U. S. 571 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 cylinder.

															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, even in favor of a
primary patent, that they are mechanical equivalents. While the
poppet valve, which, for the purposes of this case, we may term the
auxiliary valve, is, in its operation, independent of the main
valve, the word "independent" in the claims of the Westinghouse
patent evidently refers to a valve auxiliary to the triple valve,
and independently located as well as operated. The difference is
that in one case, the air from the train-pipe is introduced into
the brake cylinder separately and independently from the air from
the auxiliary reservoir, while in the other case, they unite in the
chamber, C, and pass through the same valve to the brake cylinder.
In the Westinghouse patent, there is one valve operated by the
direct thrust of the piston, opening a by-passage; in the other,
there is a poppet valve also opened by the piston, and another
valve, 26, opened by the pressure maintained upon the outside of
the partition, 9.

															It is claimed, however, by the complainants that Boyden was not
the inventor of the differential pressure theory; that there is
such a differential pressure in their own patent, caused by the
fact that the air from the auxiliary reservoir in passing to the
brake cylinder travels through a restricted port, 35, and, as the
entrance to the brake cylinder is through a much larger port, the
air is taken up by it much more rapidly than it is Page 170 U. S. 572 supplied by the restricted port, which reduces the pressure in
the by-passage so much that, when the quick action valve, 41, is
opened, the pressure from the train-pipe air is sufficient to open
the valve, 49, and admit a full volume of train-pipe air at a
pressure of 55 pounds, to the brake cylinder. The fact, however,
that no suggestion is made in the patent of such a function of the
restricted port, 35, indicates either that none such had been
discovered or that it was not considered of sufficient importance
to mention it. Indeed, it seems to have been an afterthought,
suggested by the necessity of an answer to defendants' argument,
based upon their partition 9. That when the auxiliary valve is
opened there must be a difference in pressure above and below the
check valve, 49, in order to open it is manifest, yet this is
rather an incident to the Westinghouse device than the controlling
feature that it is made in the Boyden patent. There is no
partition, in the proper sense of the word -- certainly none
located as in the Boyden device -- between the chambers, D and C,
and no aperture in such partition opened for the express purpose of
maintaining this differential pressure. If such differential
pressure existed to the extent claimed in the Westinghouse patent,
it certainly was not productive of the results flowing from the
same device in the Boyden patent.

															We are induced to look with more favor upon this device not only
because it is a novel one, and a manifest departure from the
principle of the Westinghouse patent, but because it solved at
once, in the simplest manner, the problem of quick action, whereas
the Westinghouse patent did not prove to be a success until certain
additional members had been incorporated into it. The underlying
distinction between the two devices is that, in one, a separate
valve and separate by-passage are provided for the train-pipe air,
while in the other, the patentee has taken the old triple (or
quadruple) valve, and by a slight change in the functions of two of
its valves and the incorporation of a new element (partition 9),
has made a more perfect brake than the one described in the
Westinghouse patent. If credit be due to Mr. Westinghouse for
having invented the function, Mr. Boyden has certainly
exhibited Page 170 U. S. 573 great ingenuity in the discovery of a new and more perfect
method of performing such function. If his patent be compared with
the later Westinghouse patent, No. 376,837, which appears to have
been the first completely successful one, the difference between
the two, both in form and principle, becomes still more apparent,
and the greater simplicity of the Boyden patent certainly entitles
it to a favorable consideration. If the method pursued by the
patentee for the performance of the function discovered by him
would naturally have suggested the device adopted by the
defendants, that is, in itself, evidence of an intended
infringement; but, although Mr. Boyden may have intended to
accomplish the same results, the Westinghouse patent, if he had had
it before him, would scarcely have suggested the method he adopted
to accomplish these results. Under such circumstances, the law
entitles him to the rights of an independent inventor.

															Upon a careful consideration of the testimony, we have come to
the conclusion that the Boyden device is not an infringement of the
complainants' patent, and the decree of the circuit court of
appeals is therefore Affirmed. MR. JUSTICE SHIRAS, with whom concurred MR. JUSTICE BREWER,
dissented, and filed the following opinion:

															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." In it for the first time was
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, Page 170 U. S. 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 power 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 no wise 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 Page 170 U. S. 575 as 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, the patent was for a new form
of the body of a car for the transportation of coal, thus avoiding
certain practical difficulties or disadvantages 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, that 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 a change of form, and the patentee has claimed one form
only. Patentable 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 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 rise to
questions, and the property of inventors would be valueless Page 170 U. S. 576 if it were enough for the defendant to say: 'Your improvement
consisted in a change of form. You 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 of 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 defense 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 those words." McCormick v.
Talcott , 20 How. 402, 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, he will have a right to treat as infringers all who make
machines 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 Page 170 U. S. 577 of 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, and 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 was quoted:

															"Now I think it goes to the root of this case to remember that
this is, as was described by one of the counsel, really a pioneer
invention, and it is by the light of that, as it seems to me, that
we ought to consider 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 whether the addition is
material or whether the omission is material, but whether what has
been taken is the substance and essence of the invention."

															These were cases wherein the discovery or invention was 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, was a noted case in
which the true distinction was 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 was for a
principle, said:

															"It is very difficult to distinguish it from the
specification Page 170 U. S. 578 of 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 heated 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 system 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. 284) that a patent may 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 Page 170 U. S. 579 of 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 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 being 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 , 126 U. S. 533 ,
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 could be done by gradually changing the
intensity of a continuous electric current so as to make it Page 170 U. S. 580 correspond 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 invention 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 that 'any person who has invented or
discovered any new and useful art, machine, manufacture, or
composition of matter' may obtain a patent therefor. 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 which 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 Page 170 U. S. 581 exact 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 it 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 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
call 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 Page 170 U. S. 582 by 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, were 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
employees 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 Page 170 U. S. 583 as 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
F. 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 main 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 reason 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 defendants' 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 Page 170 U. S. 584 circuit 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 BREWER concurred in the dissenting opinion.

															MR. JUSTICE GRAY and MR. JUSTICE McKENNA also dissented from the
opinion and from the decision of the Court.

Summary: The U.S. Supreme Court case of Westinghouse v. Boyden Power Brake Company (1898) dealt with a patent infringement dispute between George Westinghouse, Jr. and the Boyden Power-Brake Company over fluid-pressure brake mechanisms for trains. Westinghouse's patent, issued in 1887, described a system that used compressed air to apply brake shoes to wheels more quickly and effectively, especially for long trains. The Boyden device was found not to infringe on Westinghouse's patent. The Court's decision focused on the interpretation of Westinghouse's patent claims and the state of the art at the time. Dissenting opinions highlighted the potential dangers of modifying or invalidating a clear and definite patent based on uncertain sources of information.