This is an appeal from a decree of the circuit court dismissing a bill brought for infringement, of letters patent No. 463,569, issued November 17, 1891, to the American Bell Telephone Company as assignee of Emile Berliner. A caveat describing the invention was filed April 14, 1877, and the application for the patent June 4, 1877. The patent is for a battery telephone transmitter of the variable resistance type.
A battery transmitter is one in which a battery or strong current is utilized for the transmission of speech, as distinguished from a magneto transmitter, in which only a feeble current is generated by *894induction. It requires a battery current to transmit speech long distances. The variable resistance type of transmitter utilizes a battery current for the transmission of speech by varying the electrical resistance in the circuit. Variable resistance means simply variable obstruction to the passage of the current. Variable resistance changes the strength or intensity of the current, and, if these changes correspond to the changes in the density of the air caused by sound waves, we have a current whose electrical undulations or vibrations are similar in form to sonorous vibrations or sound waves, and which will transmit speech. In a telephone transmitter variable resistance refers to the changes in resistance which take place at the contact between the two conductors or electrodes, produced by the vibrations of the diaphragm caused by the sound waves.
The Berliner transmitter, covered by his patent in suit, utilizes a battery current for the transmission of speech by varying the electrical resistance in the circuit. The following drawing from the patent shows the Berliner telephone, in which Fig. I is the transmitter in controversy, and Fig. 2 the receiver:
threaded rod, B, which is supported by the bar, d. The pressure of the ball, C, against the plate, A, can be regulated by turning the rod, B. The ball and plate are included in cir.cuit with an electric battery, so that they form electrodes, the current passing from one of them to the other. By making the plate vibrate, the pressure at the point of contact becomes weaker or stronger as often as vibrations occur, and the strength of the current is thereby varied accordingly. *895By placing another instrument capable^ of acting as a telephonic receiver, as shown in Fig. 2, in the same electric circuit, sound uttered against the plate of Fig. 1 will be reproduced by the plate of Fig. 2; for, as the vibrations of the transmitter diaphragm caused by the sound will alternately weaken and strengthen the current as many times as vibrations occur, the diaphragm of the receiver will be caused by these electrical vibrations to vibrate at the same rate and measure. The latter vibrations being communicated to .the surrounding air, the same kind of sound as uttered against the transmitter, Fig. 1, will be reproduced at the receiver, Fig. 2. It is not essential that the plate should be of metal. It may be of any material able to vibrate, if only at the point of contact suitable arrangement is madé so that the current passes through that point. It may be of any shape or size, or other suitable vibratory medium may be used; for example, a wire. ' Any other metallic point, surface, or wire may be substituted for the ball.
From this description in the patent we find that the Berliner transmitter consists of a battery circuit with two electrodes in constant contact. One electrode is composed of a diaphragm or plate of metal or other vibratory material, and the other electrode of a metallic ball or point. Sound uttered against the diaphragm causes it to vibrate. These vibrations vary the pressure between the electrodes at the point of contact so as to strengthen and weaken the contact, and thereby vary the electrical resistance of the circuit.
The following claims are in issue:
“(1) The method of producing in a circuit electrical undulations similar In form to sound waves by causing the sound waves to vary the pressure between electrodes in constant contact so as to strengthen and weaken the contact and thereby increase and diminish the resistance of the circuit, substantially as described.
“(2) An electric speaking telephone transmitter operated by sound waves, and consisting of a plate sensitive to said sound waves, electrodes in constant contact with each other, and forming part of a circuit which includes a battery or .other source of electric energy and adapted to increase and decrease the resistance of the electric circuit by the variation in pressure between them caused by the vibrational movement of said sensitive plate.”
These claims must be- read in connection with the disclaimer of the patent, which declares that the patentee does not claim to be “the first inventor of the art of transmitting vocal and other sounds telegraphically by causing electrical undulations similar in form to the sound waves accompanying said sounds,” nor to be “the first who caused such electrical undulations by varying the resistance of an electric circuit in which a current was passing.”
In view of this disclaimer, the first claim covers only the particular method described for varying the resistance in the circuit to produce electrical undulations similar in form to sound waves, and the second claim covers only the instrument or transmitter which embodies this method.
The complainant mainly relies on the first or method claim. It is contended that the invention covered by this claim was first disclosed by Berliner in his caveat of April 14, 1877. This invention was the method of varying resistance in the circuit by varying the pressure at the point of contact between solid electrodes in constant *896•contact. This way of varying the resistance, it is said, is the same as that disclosed by Prof. Hughes a year later, on May 9, 1878, in a paper read before the Royal Society of London. Hughes called his instrument the microphone. The complainant rests its' case upon the identity of the Berliner and the Hughes methods of varying the •resistance, and upon the priority of invention by Berliner. In the language of complainant’s brief: “It cannot be seriously denied, and none of the witnesses deny, that the Hughes article and the caveat describe the same invention.” “The complainant stakes its case upon the proposition, firmly established by the testimony, that Emile Berliner was the original and first inventor of the microphone.” This position of the complainant is necessary in order to make out infringement. The defendant’s transmitters use carbon electrodes, and, unless Berliner first discovered and disclosed the microphonic method •of varying resistance, his patent must be limited to the metallic electrodes describes in the specification, and the defendants do not infringe. The issue here raised can be more intelligently considered if we briefly review the state of the art at the time Berliner made his invention.
The speech transmitting telephone presents the problem of the reproduction, by means of an electric current, of a succession of vibrations on the receiving diaphragm which shall exactly correspond to the vibrations of the transmitting diaphragm caused by the air vibrations, or sound waves, produced by the voice in speaking. The problem was rendered more difficult for the reason that the air vibrations caused by the vocal organs in articulate speech are very complex in form. •
On March 7, 1876, a little more than a year before the Berliner ■caveat appeared, Bell’s basic patent was issued, disclosing his art of transmitting speech by creating changes of intensity in a continuous ■current of electricity exactly corresponding to changes of density in the air caused by the vibrations which accompany vocal sounds. This is known as Bell’s undulatory current, which simply means an electric current whose undulations are similar in form to sound waves.
The prior current in the Reis telephone would only reproduce musical tones. It would not reproduce the finer and more complex sonorous vibrations upon which depends the quality of sound which •characterizes the human voice. This was because the current was intermittent. Bell discovered that the current must be continuous in order to impress'upon it changes which correspond to the form of sound waves.
The Bell patent also disclosed several ways of utilizing his undulatory current. One way is known as the “magneto method,” in which the current is induced or generated from the magnetic field surrounding an electro-magnet by the movements of the diaphragm caused by sound waves. These movements, by altering the condition of the magnetic field, produce a current which corresponds in form to the sound waves. An undulatory current of this kind, generated by the transmitter itself by means of the slight movements of the diaphragm, is necessarily feeble, and can only transmit speech short distances. Nevertheless, this instrument was the first practical speech transmitter, and the only commercial transmitter in use until it was *897supplanted by the carbon variable resistance transmitter. The instrument is illustrated in the following figure taken from the Bell patent:
In this drawing, a soft-iron armature, c, is caused to vibrate in front of the pole of an electro-magnet, b, by means of a membrane diaphragm, a, moved by the sound waves, to which diaphragm the armature is attached. This induces or generates an undulatory current in the coil of the electro-magnet, which current passes through another electro-magnet, f, in the same circuit, and causes its armature, h, to perform like movements to those of the armature of the transmitter, whereupon the diaphragm, i, attached to the second armature, reproduces the same sounds as are uttered into the transmitter. Bell subsequently took out a patent for an improved form of this transmitter, in which the diaphragm itself was of metal, instead of being a membrane with an,armature attached to it.
Another way of utilizing Bell’s undulatory current disclosed in his 1876 patent was by varying the resistance in a battery circuit. This is made the subject of claim 4, which is for “the method of producing undulations in a continuous voltaic current by gradually increasing and diminishing the resistance of the circuit.” The specification refers to this method and apparatus as follows:
“The external resistance may also be varied. For instance, let mercury or some other liquid form part of a voltaic circuit, then the more deeply the conducting wire is immersed in the mercury or other liquid the less resistance does the liquid offer to the passage of the current. Hence the vibration of the conducting wire in mercury or other liquid included in the circuit occasions undulations in the current.”
The art, as it was left by Bell’s primary patent, may be thus summarized: There existed the undulatory current, the only known current which will transmit speech. There existed one form of its application, known as the “magneto transmitter” or “magne.to telephone,” which went into extensive use for several years, but which would transmit speech only a short distance, owing to the feebleness of the current. There existed also another way of utilizing the undulatory current by varying the resistance in a battery circuit at the contact between electrodes in constant contact, those electrodes being a solid and a liquid. The instrument embodying this method is known as the “mercury transmitter.”
After these disclosures in the Bell patent, the problem which remained was the invention of a practical transmitter which would utilize the undulatory current by varying the resistance in a battery circuit, and so transmit speech long distances. Bell had supplied the *898current, and had shown that it could be utilized by varying the resistance in a battery circuit, and what remained was to devise a better way of varying the resistance than was pointed out by Bell. This problem was solved by two discoveries which are now embodied in every commercial transmitter. The first was the discovery of the peculiar properties of carbon in varying electrical resistance, and the second was the discovery of the remarkable effects of sound waves in varying resistance at a loose contact between solid electrodes. Edison made the first discovery, and the fundamental question for our determination in the case at bar is whether Berliner or Hughes first made the second discovery. The instrument which utilizes both these discoveries is called a “microphone transmitter.” Every microphone transmitter, as commonly understood in the telephonic art, is an instrument having carbon electrodes in loose or feeble contact. But a transmitter may still be a microphone without having carbon electrodes, provided the electrodes are of solid material, and so capable of embodying microphonic action. It is not pretended that Berliner discovered the carbon electrode, but it is maintained that he was the first to discover microphonic action, and to embody that principle in an operative speech-transmitter. If this be true, the complainant may well insist that the claims of the Berliner patent are not limited to metallic electrodes, bút cover the microphonic process or art for the reproduction of sound by varying the electrical resistance in a circuit at a loose contact between solid .electrodes in constant contact.
Before the consideration of the microphonic method, and Berliner’s priority of invention over Hughes, it may help to1 throw some light on the subject if, at this stage of our inquiry, we briefly trace the development of the variable resistance transmitter. •
After Bell’s great contribution to the telephonic art in 1876, the thoughts and efforts of inventors were largely turned in the direction of material and structure, rather than to the discovery of new methods. The only two transmitters then known which used a battery current were the Reis transmitter and the Bell mercury transmitter, and inventors naturally looked for the solution of the variable resistance transmitter problem along the lines of these instruments. A brief reference to these instruments and those which followed, until we reach the commercial carbon transmitter, will prove instructive.
The Reis transmitter employed a battery current. There was a diaphragm set in motion by sound waves, and there were two metallic electrodes in loose inconstant contact in the circuit. This instrument would transmit musical sounds, bqt not articulate speech, because at every full vibration of the diaphragm the electrodes separated, thereby interrupting the current. In structure this instrument is substantially like the Berliner transmitter. Reis failed because he had not discovered that a continuous current, which requires a constant contact between the electrodes, was essential to transmit speech. In spite of this failure, it has been truly said that the telephonic art owes much to Reis.
The next battery instrument was Bell’s mercury transmitter, described in his 1876 patent, in connection with his undulatory current. *899This instrument was operative, but not practical. A sketch, in an exaggerated form, is here given:
In this drawing A is the diaphragm, B the wire attached thereto, D the mercury or other liquid, and X and Y the circuit connections. As the diaphragm vibrates, the point E moves down and up in the mercury, thereby causing electrical undulations similar in form to sound waves. Here we have a diaphragm set in motion by sound waves, and a metallic electrode and a liquid electrode in constant contact. As the vibrations of the diaphragm cause the metal point to be immersed in the liquid, the less resistance there is to the passage of the current. The way or method of varying the resistance in this transmitter is by varying the area of contact between the two electrodes.
In February, 1877, 11 months after Bell’s patent disclosed his mercury transmitter, Edison invented what is known as the “plumbago film transmitter.” This instrument utilized Bell’s undulatory current in a battery circuit by varying the resistance between solid electrodes in constant contact. It was an operative instrument, but not practical. A sketch of the instrument is here reproduced:
JUdi&on/ B-ll.
*900This drawing represents a disk of hard rubber coated with plumbago, which presses against the tinfoil sheet on the diaphragm. One of the line wires is connected to the disk at its upper edge, and the other to the tinfoil sheet on the diaphragm. This sketch was the original from which was made the application for patent No. 474,230. In this instrument we have a diaphragm set in motion by sound waves, and two solid electrodes in constant contact. The vibrations of the diaphragm due to the sound waves caused it to come into greater or less contact with the disk, and so varied the resistance in the circuit. The thin film of plumbago on the disk being a poorer conductor than the metal diaphragm, the movements of the diaphragm cut in and out the resistance of the circuit. The way or method of varying the resistance in this transmitter would seem to be by varying the extent or area of contact surface between the electrodes caused by the vibrations of the diaphragm1, although the patent also speaks of the vibrations as causing an increase and decrease of electric energy according “to the intimacy of contact between the vibrating diaphragm and the surface of the adjacent disk.”
We come next to Edison’s plumbago cylinder transmitter, which bears the date of April 1, 1877, and which is described in its final form in patent No. 474,231. This instrument also utilized Bell’s undulatory current in a battery circuit by varying the resistance between solid electrodes in constant contact. It was an operative speech transmitter, but not practical. A sketch of this instrument is here given:
Edison/ S&-22*
This apparatus comprised a diaphragm in contact with a series of plumbago cylinders mounted on stiff springs, which held them in a state of contact. The diaphragm was in constant contact with the plumbago at one end of the series, and by its vibrations varied the resistance in the circuit. In this instrument we have a diaphragm set in motion by sound waves, and' solid electrodes in constant contact. The vibrations of the diaphragm compressed the mass of plumbago, which caused variations of resistance in the circuit. The way or method of varying the resistance in this transmitter is by varying the compression of the mass of plumbago caused by the vibrations of the diaphragm. There would seem to be little doubt that microphonic *901action would be present in this transmitter, provided the adjustment between the diaphragm and the plumbago cylinders were such as to make a loose initial contact between them.
Next in the order of time is the Berliner transmitter in suit, described in his caveat of April 14, 1877. This instrument, as we have seen, also utilizes Bell’s undulatory current in a battery circuit by varying the resistance between solid electrodes in constant contact. It was an operative speech transmitter. It never went into use, however, as it was not a practical instrument. For the sake of clearness, the drawing of the transmitter is again reproduced:
In this instrument we have a diaphragm set in motion by sound waves, and two metallic electrodes in constant contact. The vibrations of the diaphragm vary the pressure at the point of contact, and thereby vary the resistance in the circuit. The way or method of varying the resistance in this transmitter is by varying the pressure at the point of contact, and so varying the intimacy of contact between the electrodes. When the electrodes in this instrument are so adjusted as to be in loose contact we have present microphonic action, and the instrument becomes a microphone transmitter. It may here be observed, however, that our inquiry is not whether the Berliner instrument became a microphone when properly adjusted, but whether Berliner first discovered the microphonic way of varying resistance, and made it ’known to the world in his caveat.
This brings us to Edison’s carbon transmitter, which was invented in the fall of 1877, and is found in patent No. 203,016, dated April 30, 1878. The instrument utilizes Bell’s undulatory current in a battery circuit by varying the resistance between two solid electrodes, one of which is carbon. The accompanying figure show's the commercial instrument:
*902In this figure, D is the metal diaphragm resting by means of the small brass tube, A, upon a disk of hard rubber, G, beneath which is a thin plate of platinum foil, P, connected with the battery. Beneath this platinum foil is a button of soft carbon, C, made of highly compressed lampblack, and beneath this is another thin plate of platinum foil, which is connected to the line through the frame of the instrument. The carbon button, with its inclosing plates, was so mounted as to be capable of adjustment by means of a screw. In this instrument we have a diaphragm set in motion by sound waves, and two solid electrodes in constant contact, one of the electrodes being composed of carbon. “The vibrations of the diaphragm,” in the words of the patent, “subject the carbon to different pressures, according to the amplitude of motion resulting from the sound waves, and this difference of pressure varies the resistance offered by the carbon to the passage of the current, and produces a rise and fall of electric tension.” • The way or method of varying the resistance in this transmitter is by varying the pressure at the contact, and so varying the intimacy of contact between two solid electrodes. In this instrument Edison disclosed to the world his discovery of the special properties of carbon in varying resistance in a telephone transmitter. When the electrodes in this instrument are adjusted in feeble contact, it becomes a microphone.
The Edison carbon transmitter was the first practical long-distance speech transmitter which utilized Bell’s undulatory current in a battery circuit by varying the resistance in the circuit. The commercial art passes at once from Bell’s magneto transmitter to Edison’s carbon transmitter. In December, 1879, there were 34,000 magneto transmitters in use, and 18,000 variable-resistance carbon transmitters. Subsequently the use of the magneto transmitters declined, and they were supplanted by the carbon transmitter. All variable resistance transmitters commercially used have carbon electrodes in loose contact. The alleged infringing transmitters in the case at bar are mere improvements in the structure, form, or adjustment of the Edison carbon transmitter, invented by him in the fall of 1877.
We now pass to the crucial point upon which the complainant rests its case. The complainant’s position on this point may be stated as follows:
Berliner first discovered the microphonic method of varying resistance, and first disclosed this method, and an operative instrument embodying it, in his caveat of April 14, 1877. In other words, Berliner first invented the microphone. Bell’s mercury transmitter and Edison’s plumbago film and plumbago cylinder transmitters are not anticipations, because they do not operate by the microphonic method. They are not microphones. On the other hand, Edison’s carbon transmitter and the two carbon transmitters made or used by the defendants infringe the Berliner patent, because they employ the microphonic method, and are microphones. The microphonic method is not limited to the use of the carbon electrode, but only to the use of solid electrodes, or hard and unyielding electrodes'; and therefore the carbon electrode, when there is microphonic action, is within the microphonic method, and infringes the Berliner patent. The *903microphonic method was disclosed to the scientific world by Professor Hughes in May, 1878, and was regarded as a wonderful discovery. Hughes called his instrument a microphone, from analogy to the microscope, since he believed it would magnify small sounds. The microphonic method of varying resistance, disclosed by Hughes in 1878, was the same as the microphonic method of varying resistance disclosed by the Berliner caveat in 1877. To be sure, the Hughes instrument, which he was the first to term' a microphone, was constructed of carbon electrodes; but this is immaterial, because he states that the best material for the electrodes has not yet been discovered, and because his discovery resides in the method of varying the resistance, and not in the materials composing the electrodes. The disclosure by Berliner of the Hughes method of varying resistance is found by the complainant in the following passages from Berliner's patent, which also appear in substantially like form in his caveat:
“It is a fact that if at a point of contact between two conductors forming part of an electric circuit and carrying an electric current the pressure between both sides of the contact becomes weakened the current passing becomes less intense; as, for instance, if an operator on a Morse instrument does not press down the key with a certain firmness the sounder at the receiving instrument works much weaker than if the full pressure of the hand had been used. Based on this fact, I have constructed a simple apparatus for transmitting sound along a line of an electric current in the following manner:
“In Figures 1 and 2 of the drawings, A is a metal plate well fastened to the wooden box or frame, but able to vibrate if sound is uttered against it or in the neighborhood of said plate. Against the plate and touching it is the metal ball, 0, terminating the screw-threaded rod, B, which is supported by the bar or stand, d. The pressure of the ball, O, against the plate, A, can be regulated by turning the rod, B. * * * By making the plate vibrate the pressure at the point of contact, a, becomes weaker or stronger as often as vibrations occur, and the strength of the current is thereby varied accordingly, as already described.”
The Berliner invention above described consists in the method of varying the resistance by variation of pressure at the point or points of contact between solid electrodes in constant contact.
To determine whether this invention is the same as the Hughes method of varying resistance, it is necessary to have a clear understanding of the nature of the discovery which he revealed to the world on May 9, 1878.
Such portions of the Hughes article as seem material may be summarized as follows:
The introduction of the telephone led Prof. Hughes to investigate the effect of sonorous vibrations upon the electrical behavior of matter. Sir William Thompson and others had shown that resistance to the passage of currents afforded by wires is affected by their being placed under strain, and, inasmuch as the conveyance of sonorous vibrations induced rapid variations in the strain at different points of a wire, Prof. Hughes believed that the wire would vary in its resistance when it was used to convey sound. To investigate this he made a rough telephone receiver or “sound detector,” which he connected in line with a battery current in a closed circuit. The apparatus or materials experimented upon were used in the same way as the trans*904mitter of the speaking telephone of Bell. The following is a sketch of his apparatus:
In this drawing, B is the battery, S the source of sound or material examined, and T the telephone. He then proceeds:
"I Introduced into the circuit at S a strained conductor,-a stretched wire,listening attentively with the telephone to detect any change that might occur when the wire was spoken to, or set into transverse vibrations by being plucked aside. Gradually, till the wire broke, the strain was varied, but no effect whatever was remarked except at the moment when the wire broke. The effect was but momentary, but invariably, at the moment of breaking, a peculiar `rush' or sound was heard. I then sought to imitate the condition ot the wire at the moment of rupture, by replacing the broken ends, and pressing them together with a constant and varying force by the application of weights. It was found that if the broken ends rested upon one another with a slight pressure, of not more than hone ounce to the square inch on the joints, sounds were distinctly reproduced, although the effects were very imperfect."
Prof. Hughes had now discovered microphonic action, or the mode of operation of the instrument which he calls the microphone, and all that follows in his paper is only the further development of this principle. He sought to investigate the effect of sonorous vibrations or sound waves upon the electrical behavior of matter, and he began his investigation with the belief that such vibrations wouid vary the electrical resistance of wire under strain. He found no marked effect until the moment when the wire broke or parted contact, when he detected a peculiar "rush" or sound. He then imitated the condition of the wire at the moment of rupture by replacing the broken ends in the apparatus, and pressing them together with a constant and varying force by the application of weights. He discovered that, if the broken ends rested together with a slight pressure of not more than one ounce to the square inch on the joints, sounds were distinctly reproduced. Thus Prof. Hughes, by a process of deduction and experiment, and advancing step by step, made his great discovery of the effects of sonorous vibrations in varying electrical resistance at a feeble or loose contact between two electrodes. When Prof. Hughes placed the two ends of the ruptured wire in contact, he had not discovered micro-phonic action. When the ends were pressed together with considerable pressure, he had not discovered microph9nic action. When the ends were in a very loose contact, he had not discovered microphonic action. But when, after repeated experiments with different degrees of pressure, the broken ends rested upon one another with a slight or feeble contact, his hopes were realized. Hughes did not, like Bell, discover a new current, but he did make known the close affinity between sound waves and an electric current at what electricians were *905accustomed to term a “bad joint” in an electric circuit. He discovered the sensitiveness, the adaptability, of the current at a loose or light contact to vary its resistance in conformity with the vibrations of the air produced by sound waves. He discovered a new way of varying resistance which has proved of great utility in the telephonic art. Unless anticipated by Berliner, he was the first to disclose this new way, although previously it may have been present in telephone transmitters without the knowledge of the inventors. Prof. Hughes’ discovery lay in loose initial contact between the electrodes. This is the essence of the microphone. With loose initial contact there is microphonic action; without loose initial contact there is no efficient microphonic action. When the contact between the electrodes is greater or less than a feeble contact, such action is either greatly impaired or ceases altogether. Microphonic action, or the microphonic method, or the microphonic process or art, discovered by Prof. Hughes, is simply the effects of sonorous vibrations in varying resistance at a feeble or loose contact between solid electrodes in constant contact, whereby sound is reproduced at the receiver. Microphonic action is dependent upon three simple conditions,—atmospheric vibrations produced by sound waves, two solid electrodes in feeble contact in a line circuit, and a sound-receiving instrument in the circuit. What produces these effects is unknown. Prof. Hughes believed the effects were “due to a difference of pressure at the different points of contact,” and that they were “dependent for the perfection of action upon the number of these points of contact.” Prof. Bell doubted this, and attributed the effects to “a variation in the amount of contact” .supplemented by the heat produced at the point of contact. But what causes these effects is immaterial. What we know is that the phenomenon exists, and was disclosed by Prof. Hughes in this article.
It may here be observed that the discovery of Prof. Hughes relates to the direct effect of the sonorous vibrations upon a loose contact, and that it is not essential to use a diaphragm. , The introduction of a diaphragm merely signifies that the sonorous vibrations produce corresponding vibrations in the diaphragm which affect the resistance at the loose contact exactly the same as the direct impact of the sound waves.
We will now resume the consideration of the article from the point where Prof. Hughes discovered microphonic action.
He found it was not necessary to join two wires endwise together to reproduce sound, but that any portion of an electric conductor would do so even when fastened to a board or to a table, and no matter how complicated the structure upon this board, or the materials used as a conductor, “provided one or more portions of the electrical conductor were separated, and only brought into contact by a slight but constant pressure.” If the ends of the wire, terminating in two common French nails laid side by side and separated from each other by a slight space, were electrically connected by laying a similar nail between them, sound could be reproduced. “Up to this point,” he continues, “the sound or grosser vibrations were alone produced; the finer inflections were missing, or, in other words, the ‘timbre’ of the Poice was wanting; but in the following experiments the ‘timbre’ became more and more perfect, until it reached a perfection leaving *906nothing to be desired. I found that a metallic powder, such as the white powder—a mixture of zinc and tin—sold in commerce as ‘white bronze,’ and fine metallic filings, introduced at the point of contact, greatly added to the perfection of the result. At this point, articulate speech became clearly and distinctly reproduced, together with its timbre; and I found that all that now remained was to discover the best material and form to give to this arrangement its maximum effect.” The paper then proceeds with a description of his experiments with the best material and form to give the maximum effect. He found carbon an excellent material, but he obtained the best results from mercury in a finely divided state. He refers to the fact that in his experiments the diaphragms of Reis, Edison, and Bell have been “altogether discarded,” and that “the variations in the strengths of the currents flowing are produced simply and solely by the direct effect of the sonorous vibrations.”
After describing the instrument which he calls a microphone, he says:
“The best form and material for this instrument, however, have not yet been fully experimented on. Still, in its present shape, it is capable of detecting very faint sounds made in its presence. If a pin, for instance, be laid upon or taken off a table, a distinct sound is emitted; or, if a fly be confined under a table glass, we can hear the fly walking, with a peculiar tramp of its own. The beating of a pulse, the tick of a watch, the tramp of a fly, can thus be heard at least a hundred miles distant from the source of sound.”
He further says:
“It is quite evident that these effects are due to a difference of pressure at the different points of contact, and that they are dependent for the perfection of action upon the number of these points of contact. Moreover, they are not dependent upon any apparent difference in the bodies in contact, but the same body, in a state of minute subdivision, is equally effective.”
The instrument he devised is described as follows:
“The microphone, in its present form, consists simply of a lozenge-shaped piece of gas carbon, one inch long, quarter inch wide at its centre, and one eighth of an inch in thickness. The lower pointed end rests as a pivot upon a small block of similar carbon. The upper end, being made round, plays free in a hole in a small carbon block, similar to that at the lower end. The lozenge stands vertically upon its lower support. The whole of the gas carbon is tempered in mercury, in the way previously described, though this is not absolutely necessary. The form of the lozenge-shaped carbon is not of importance, provided the weight of this upright contact piece is only just sufficient to make a feeble contact- by its own weight. Carbon is used in preference to any other material, as its surface does not oxidize. A platinum surface in a finely divided state is equal, if not superior, to the mercurized carbon, but more difficult and costly to construct. I have also made very sensitive ones entirely of iron.”
A Hughes microphone is shown in the following sketch:
*907In this figure, B and D are two pieces of wood fastened together, with their planes at right angles to each other. Attached to B are two small blocks of carbon, C, C. Between these a light rod, A, of carbon, is supported on small cups in C, C. If this microphone is joined in circuit with a telephone and a small battery, the vibrations produced by a fly walking on the base, D, can be distinctly heard in the telephone.
Another sketch of a Hughes microphone is also reproduced:
In this drawing, the pointed piece of carbon, C, sets loosely in the notches of two pieces of carbon, A, B. If we place our ear at the telephone, T, we shall hear distinctly not only the ticking of the watch, but the friction of the wheels.
Prof. Hughes’ article was regarded by the scientific world as disclosing a remarkable discovery. The Journal of the Franklin Institute of June 19, 1878, said:
“Prof. Hughes * * * discovered that when two or more electrical conductors rested lightly upon each other, the variation in the force of contact, caused by exceedingly feeble sonorous vibrations, would so vary the electrical resistance as to take up and transmit these vibrations to the distant telephone with great force and distinctness.”
The Russian Messenger, in describing Hughes’ discovery, said:
“It occurred to Hughes to investigate whether the transmission of sound waves by a wire had any influence on its ability to conduct a galvanic current. If so, then the change of strength of current ought to act on the telephone, and the latter ought to transmit to us the sound. For a long time Hughes’ experiments with a tightly drawn wire were without success; but fortunately, because of its great tension, the wire broke. Not wishing to stop his experiment, Hughes temporarily tied the ruptured ends, and to his astonishment he noticed that after the rupture of the wire the telephone began to transmit sounds much better. Minutely investigating this phenomenon he soon convinced himself that the transmission of sounds by telephone is best accomplished when the ends of the wire touch each other lightly, or, better still, when they are at a certain distance from each other, and between them, in light contact with them, there is another body of good electric eonductibility; for example, an iron or brass plate or a piece of carbon. The slightest sound or noise produced near that piece of carbon naturally causes the latter to vibrate. In consequence of these vibrations there is a greater or lesser contact of the conductors of the current, and therefore the latter meets in the circuit a varying resistance, and consequently its strength also varies.”
It will be impossible, in our opinion, to find in the Berliner caveat or patent any conception of Hughes’ discovery. It would seemingly *908appear that Berliner had not advanced so far in his conception of microphonic action as Hughes at the moment he heard a “rush” or sound when the ends of the wire parted contact. It will certainly be made plain that Berliner’s conception extended no further than the time when Hughes placed the broken ends of the wire in contact, and began his experiments on the effect of sonorous vibrations at different degrees of constant pressure, which finally led to his discovery of microphonic action.
Always keeping in mind that microphonic action involves the conception of sonorous vibrations and loose contact between electrodes, let us turn to Berliner’s conception and invention.
Berliner, as appears from his testimony, having already become familiar with Bell’s 1876 patent, commenced in January, 1877, “making experiments” in “the speaking telephone.” “Some time,” he says, “during that month, one of -the operators in the fire-alarm office in Washington, in showing me about the use of the Morse key, explained the importance of pressing the key down firmly upon its rest or base in order to insure the operation of the sounder promptly. He explained that if the key was not firmly pressed down the sounder might fail to respond promptly, and that was a reason why female operators were often objected to because they did not have sufficient strength to give a good contact between the key and its rest. It immediately occurred to me that, if a variation of contact pressure between the circuit-closing key and its rest could produce a variation in the current, then a varying pressure between the points of contact could be obtained by the vibration of one or both of them imparted to them by sounds or sound waves in the air in their neighborhood.”
Manifestly, the conception here given is not Hughes’ conception; because the essence of microphonic action, which resides in loose contact, is entirely wanting. When the operator told Berliner that the more firmly the fire-alarm key was pressed down the more promptly the sounder operated, he was merely stating a scientific fact, then well known, that the closer the contact ends of a wire in an electric circuit are pressed together the less the resistance, and consequently the greater the strength of the current. . Acting upon this information, Berliner says it occurred to him that, if a variation of contact pressure between the circuit-closing key and its rest could produce a variation in the current, then a varying pressure between the points of contact could be obtained by the vibration of one or both of these electrodes, imparted by sound waves in their neighborhood. Berliner’s conception of a telephonic transmitter was .this: Starting with the electrodes, in contact, he conceived that a varying pressure between the. points of contact, and a consequent varying of the strength of the current, could be obtained by the vibration of one or both of the electrodes caused by sound waves. This conception does not reach to the character of the initial contact, and therefore does not even approach microphonic action.
Suppose Prof. Hughes had stopped his experiments when he had' placed the ends of the severed wire in contact, he would riot have discovered microphonic action. Or suppose, after the wire broke, he had said, “I then placed the two ends of the wire in contact, and found that *909the sonorous vibrations would vary the pressure at the points of contact, and so vary the strength of the current, whereby sound was_ reproduced,” he would have made no discovery of microphonic action. If, however, Hughes had embodied this conception in a telephone transmitter, he would have made an invention, in that he had discovered that the minute atmospheric vibrations due to sound waves would sometimes so vary the pressure between the points of contact of metallic electrodes as to strengthen and weaken the current, and so reproduce sound. And this is exactly the scope of the Berliner con-, ception, and of his invention. His conception, by reason of the absence of any comprehension of microphonic action, when embodied^ in a transmitter, produces an instrument which is sometimes operative and sometimes not. If, by accident, the electrodes are adjusted in loose initial contact, or microphonic contact,, the instrument may be operative, while, if not so adjusted, it is inoperative.
But while Prof. Hughes, under such circumstances, would have made an invention, he could not have seriously asserted that he had discovered microphonic action; because we know that, when he placed the ends of the wire in contact, he had not made his discovery, and that it was only after repeated experiments with all degrees .of contact pressure he found the ends must be placed in loose contact to insure the reproduction of sound.
Contact, or points of contact, are meaningless as a conception of microphonic action. So, likewise, is the conception of varying pressure at the contact or points of contact. A contact, or points of contact, affected by varying pressure, may be a firm' contact, in which case there is no microphonic action, or a very loose contact, in which case there is no microphonic action, or any other degree of contact where microphonic action is not present. Microphonic action resides in the conception of a loose initial contact between the electrodes, and it is immaterial to this conception how the sound waves affect such a contact, whether by varying pressure or not. This shows that it is only the clear comprehension of loose contact which can be held to be a conception of microphonic action. A conception of microphonic action which omits loose contact leaves out the very essence of the thing to be conceived.
Berliner testified to this conception of his invention on April 12, 1879, in some interference proceedings. This was two years after the filing of his caveat, and one year after the publication of the Hughes article. So far as this description of his invention may differ from that found in his caveat, we must, of course, be guided by the latter. It is the invention disclosed in the caveat upon which the complainant must, and does in fact, rely.
Berliner begins his caveat by the statement of the fact which the operator had previously told him, though he now speaks of the pressure at “a point of contact” instead of the pressure between “the points of contact”:
“It is also a fact that if, at a point of contact between two ends of a galvanic current, the pressure between both sides of the contact becomes weakened, the current passing becomes less intense; as, for instance, if an operator ■on a Morse instrument does not press down the key with' a certain firmness, •the sounder at the receiving instrument does work much weaker than if the *910full pressure of the hand would have been used. Based on these two facts, I have constructed a simple apparatus for transmitting sound along a line of a galvanic current in the following maimer.”
The drawing of the transmitter is here reproduced:
“In the drawing accompanying this caveat, B is a metal plate well fastened to the wooden box or frame, A, but able to vibrate if sound is uttered against it or in the neighborhood of said plate. Against the plate and touching it is the metal ball, 0, which rests on the bar or stand, F, and presses against the plate, which pressure, however, can-be regulated by the thumb-screw, D, attached to the ball. By making the plate vibrate, the pressure at. the point of contact, a, becomes weaker or stronger as often as vibrations occur, and according to it from which side of the plate the sound comes.”
It is impossible to find in this language any description of micro-phonic action.
Referring to the figure, Berliner says:
“Against the plate, and touching it, is the metal ball, O, which * * * presses against the plate, which pressure, however, can be regulated by the thumb-screw, D, attached to the ball.”
This is simply saying that the electrodes are in constant contact, and that the degree of contact may be regulated by the thumb-screw. But in what manner it is to be regulated, or what is to be the degree of pressure caused by such regulation, the caveat is silent. Presumably, by experiment with different degrees of adjustment, the pressure between the electrodes is to be so regulated that the instrument will operate to transmit speech. But how can this be said to be a disclosure of microphonic action ? The operator gets no knowledge from this description of the degree of initial contact pressure which is necessary. If he presses the ball and plate too closely together, the instrument becomes inoperative. If the contact is too loose, a like result follows. But if, after frequent attempts, he happens to make such an adjustment as gives a feeble contact between the ball and the plate, the instrument may become operative. Can it for a moment be maintained that this is the discovery revealed by Prof. Hughes?
The caveat continues:
“By making tbe plate vibrate [by sound waves] tbe pressure at tbe point of contact, a, becomes weaker or stronger, as often as vibrations occur.”
This may all be true, and this feature may have involved invention, but it has no bearing on the disclosure of microphonic action. These words are merely descriptive of what takes place after some kind of an adjustment between the ball and plate has been made. The discovery of microphonic action resides in the particular kind of adjustment, and not in the fact that after such an adjustment the vibrations *911of the diaphragm caused by sound waves vary the pressure at the point of contact.
To make still more clear the distance which separated Berliner from any conception of microphonic action, we may turn to another passage from his caveat, which says:
“Same instrument to be used as a transmitter of sound waves, by uttering sound against or in tbe neigbborbood of tbe said plate or its meebanical equivalent, thus vibrating tbe plate and diminishing tbe amount of electricity passing as many times and as much as the vibrations will loosen the pressure of contact, as described.”
Berliner’s mind was still full of what the operator had told him about the fire alarm. He believed, as this passage shows, that the electrodes must be first firmly pressed together, in which case the current would flow freely, and that the vibrations of the plate due to sound waves would lessen the pressure o'f contact, and so diminish the amount of current flowing as often as the vibrations occur. He consequently started with a firm initial contact between the electrodes, and his theory was that the vibrations of the diaphragm would lessen the contact. This is the reverse of microphonic action, which starts with a loose initial contact, and, consequently, a greatly diminished flow of current.
On April 30, 1877, 16 days after the filing of the caveat in suit, Berliner filed another caveat, which describes an ingenious arrangement for “producing sound by the noise of sparks.” On May 9, 1877, nine days afterwards, Berliner filed a third caveat for what is known as his “double-pin instrument.” This was for an improvement on the ordinary make and break transmitter, by the use of a double contact. Then follows, on June 4, 1877, the application for the patent in suit, covering, with the receiver, single-pin transmitters and double-pin transmitters, continuous currents and intermittent currents, in such a confused way that an intelligent and satisfactory interpretation of this document bids defiance to the human understanding. The obscurity of the paper may be in part accounted for by the blunders of the solicitor’s clerk, but not wholly; for it is quite manifest that Berliner’s ideas at this time as to the best form of transmitter, and the principle of its operation, were unsettled and needed clarification. This course of action on the part of Berliner may not be conclusive of anything. It is sometimes unsafe to infer too much from a subsequent line of conduct. In this particular case, however, we think this much may be said with truth:
Assuming that Berliner on April 14, 1877, had already made Hughes’ discovery of microphonic action, his caveat of May 9th and his application of June 4th become incomprehensible.
In this connection it may be noticed that, in his two patents for microphones, No. 222,652 and No. 224,573, applied for more than two years after his caveat, and more than a year after the publication of the Hughes article, Berliner describes the necessity of loose initial contact between the electrodes. In the first instance, one of the electrodes, which is preferably of carbon, is described as “just in contact by its own weight with said plate,” and in the claim as “the said non-, elastic pin resting solely by its own weight upon the diaphragm.” *912The second patent is for maintaining the carbon pin constantly in light contact with the diaphragm “by the action of gravity,” or, in the words of claim x, “an opposite electrode maintained in contact with the vibrating surface by the action of gravity.” Here is the loose initial contact of Hughes, and the maintenance of such a contact during the operation of the instrument.
Berliner’s attempts to make his transmitter reproduce speech were hardly satisfactory; but, as the evidence stands, he succeeded in reproducing some words, and indistinct sentences, so that it may be said there was the transmission of the quality of sound which characterizes the human voice in speaking. In his experiments with the instrument, he says nothing about loose contact between the electrodes, or the necessity of such contact. That his efforts were not more successful he believes was owing to the crudeness of the apparatus and the difficulty of adjusting it. His apparatus, however, was not more crude than the apparatus which Hughes used in his experiments. The unsatisfactory character of Berliner’s efforts cannot be wholly ascribed to this cause, nor to the fact that he used metallic electrodes, which, for several reasons, are difficult properly to adjust, nor to both of these causes combined, but must have been due, at least to some extent, to his ignorance of microphonic action. Had he known of Hughes’ discovery, the results, in all probability, would have been much more satisfactory. Subsequent experiments, however, have shown that the Berliner instrument can be so adjusted as to become an operative speech transmitter. But the experts who made these experiments, years afterwards, had been long familiar with Hughes’ disclosure of microphonic action, and they knew the absolute necessity of loose initial contact between the electrodes in order to make the instrument an operative speech transmitter. They certainly possessed this advantage over Berliner, and the success of their efforts may be attributed in part to this cause.
The complainant’s contention that Hughes’ discovery of micro-phonic action is disclosed in the Berliner caveat rests upon general •definitions of the microphone and of Berliner’s invention rather than üpon a critical analysis of the actual discovery revealed by Hughes in his article or a critical examination of the Berliner caveat.
The definition of the Berliner invention is founded on what the complainant conceives to be the “true definition of a microphone,” which is'as follows:
“The essence of the microphone consists, therefore, in varying the resistance at the ‘joint’ or point of contact between two electrodes by varying the pressure between them.”
But this is not descriptive of the microphone, or of microphonic action, as disclosed by Hughes. “A joint” may be either tight or loose, and a “point of contact” may be either firm or feeble, and the difference between a joint and a loose joint, and a point of contact and a feeble point of contact, is the difference between what is a microphone and what is not a microphone. This is confirmed by the testimony of complainant’s experts.
Prof. Cross says, defining microphonic action:
*913“It is a fact that, when a current passes from one electrode to another kept loosely In contact with it, there is a certain resistance of passage or ‘transition resistance,’ as It may be called, at the surface of contact between the two electrodes.”
And Prof. Wright says:
“When transmitting speech, the electrodes of a microphonic transmitter are brought together with a pressure which is very light, and which has been determined by experiments to vary within a comparatively narrow range.”
This error is present in every definition of the microphone and of the Berliner invention in complainant’s brief, and it permeates and undermines the fundamental position on which it rests the case.
Again, the Berliner invention is defined as “varying the pressure at a point of contact between electrodes,” or “varying the pressure between two electrodes in contact, and thereby varying the resistance in the circuit so as to produce undulatory sound waves.” More fully stated, the definition may be expressed as follows: The method of varying resistance by variation of pressure at the point of contact between solid electrodes in constant contact. These definitions are not descriptive of the microphone or of microphonic action, because they omit any reference to loose contact between the electrodes.
The complainant then proceeds to define what it calls Prof. Hughes’ “brilliant and radically novel discovery” in substantially the same terms, as follow's:
“It was recognized that the essence of this discovery lay in the variation of pressure at a point of contact between two electrodes in a galvanic circuit, thereby varying the resistance which such ‘joint’ offers to the passage of the current.”
Again:
“The method of varying resistance by varying the pressure at a point of contact between electrodes, which was set forth in Berliner’s caveat and subsequently in Professor Hughes’ article, was instantly recognized as solving the problem of the ‘battery-speaking telephone.’ ”
Again:
“Hughes says that he may use one contact (like two ends of wire) or a larger number of points of contact, and that he may use either metal or carbon contacts; the one essential thing being the ‘difference of pressure at the different points of contact.’. Berliner’s caveat describes the invention as resting on variation of pressure at a point of contact between the electrodes, and says that the plate which forms one of the electrodes may be of any material, and that there may be more than one point of contact.”
From these comparisons follows this conclusion:
“It cannot be seriously denied, and none of the witnesses deny, that the Hughes article and the caveat describe the same invention.”
In this comparison of the Berliner and Hughes inventions it will also be observed that no mention is made of loose contact, or feeble contact, or light contact, and that, consequently, all of these descriptions are wanting in any reference to the essence of microphonic action. What Hughes disclosed to the world, as we have seen, was not varying the pressure at the point of contact; nor did the essential thing which he discovered lie in the difference of pressure at different points of contact. His discovery resided in loose contact, or rather *914in the remarkable effects of sonorous vibrations in varying resistance at a loose contact. He also made loose contact between the electrodes the indispensable feature of his microphone. In describing that instrument in his article he says: “The form of the lozenge-shaped carbon is not of importance, provided the weight of this upright contact piece is only just sufficient to make a feeble contact by its own weight.” He believed that these effects were due to pressure at the points of contact. This, however, was simply his theory of what took place,—his theory of microphonic action. Except in alluding to this theory near the close, the word “pressure,” throughout the article, has reference to initial contact pressure. “Variation of pressure at a point of contact’ may be descriptive of Berliner’s invention, but, to say the least, it is a mistaken and misleading description of microphonic action and of Prof. Hughes’ discovery.
Again, the first and most important claim of the Berliner patent fails to define-the microphonic method of Hughes. The claim is for “the method of producing in a circuit electrical undulations similar in form to sound waves by causing the sound-waves to vary the pressure between electrodes in constant contact so as to strengthen and weaken the contact, and thereby increase and diminish the resistance of the circuit.” It will be observed that the claim is silent as to the character of the initial contact between the electrodes. The claim must be read as if written April 14, 1877, a year before the Hughes discovery. With such knowledge of the telephonic art as existed at that time, no one would have known from this description of the Berliner method that the electrodes must be adjusted in a loose initial contact. In omitting any reference to loose contact, the claim fails to disclose the essence of the Hughes microphonic method.
The complainant has rested its case on the prior discovery by Berliner of microphonic action as disclosed by Prof. Hughes in -his article of May 9, 1878. We are of the opinion that Berliner had no conception of this discovery, that he does not disclose such discovery in his caveat or patent, and that, if his transmitter operated as a microphone, it did so without any knowledge on his part of the microphonic principle. The world was left in the same ignorance of' microphonic action after the appearance of his caveat as before. If Prof. Hughes had had lying on his table a Berliner transmitter and the Berliner caveat, they would have revealed nothing to him, nor have been of any assistance in the experiments which resulted in his discovery of the remarkable effects of sound waves in varying electrical resistance at a loose or feeble contact. If he had taken the diaphragm and metal ball of the Berliner instrument in place of the ends of his wire, he must have gone on experimenting with the effect of sonorous vibrations at different degrees of initial pressure between the plate and ball, until he had discovered that only with a slight pressure, or feeble contact, is there microphonic action. Prof. Hughes’ discovery cannot be read into the Berliner caveat or the claims of the Berliner patent.
In connection with-the invention set forth in the Berliner caveat, the complainant’s experts dwell on “transition resistance,” an'd the fact that such resistance varies enormously with pressure. “Transition resistance” is only another name for loose-contact resistance, or micro-*915phonic resistance, and it was Hughes, not Berliner, who discovered transition resistance in the telephonic art, and the effects of sound waves in varying such resistance.
It was in its rebuttal testimony that the complainant fully brought out its contention that Berliner was the prior inventor of the microphone. In the opening testimony the complainant seemed to rely' more upon the variable pressure theory of the Berliner invention. Prof. Cross, adopting Prof. Barker’s language in the Government Case, defines the invention of the Berliner patent as “a transmitter whose operation was based upon the variation of electrical resistance by variation of contact pressure.” Again Prof. Cross says:
“It is what is known as a variable pressure contact transmitter. It operates, not as did the magneto transmitter to generate the undulatory current produced by the small amount of energy which the voice can communicate to the transmitter, but simply to impress upon the electrical current furnished from another source—practically a battery—variations in strength which correspond to the motions impressed by the voice upon the transmitter. The current from the battery in flowing through the two electrodes (as they are called) of the transmitter, when these are set into vibration by the voice, is molded by their variations of pressure into a shape similar to that of the air vibrations of the air particles themselves; that is, it is molded into Mr. Bell’s undulatory current.”
“Pressure” and “variation of pressure” in the telephonic art usually refer to the effects of the movements of the diaphragm caused by sound waves at the contact between the electrodes. In every variable resistance transmitter the sound waves vibrate the diaphragm, and the movements of the diaphragm cause vibrations of pressure at the surface contact between the electrodes, which vary the resistance, and thereby reproduce speech.
“Variable pressure,” however, in connection with the Berliner invention, is used by the complainant in a special sense. It signifies variations of pressure which vary the intimacy of contact between solid electrodes, and so vary the resistance, as distinguished from variations of pressure which vary the area of contact between a solid electrode and a liquid electrode, or the area of contact between two solid electrodes, or vary the compression of the mass between solid electrodes.
These distinctions may be further illustrated: If we cut the wire in an electric circuit, and place the severed ends in contact, it will be found that, by varying the pressure at the contact, the resistance will be varied, and consequently the strength of the current. This was a well-known fact in electrical science long before 1876. Here the variation of pressure may be said to vary the resistance by varying the intimacy of contact at the surface ends of the wire, although it is manifest that the varying pressure must also cause, in some slight degree, a varying area of contract. If, instead of two ends of a wire, we have one end of a wire and a liquid in constant contact, it is apparent that by pressing the wire down more or less, or by varying the pressüre on the wire, the resistance will be varied, and consequently the strength of the current. Here variation of pressure may be said to vary the resistance by varying the area of contact, although the intimacy of contact also will be varied in some degree. Again, if in place of the two ends of a wire, or the end of a wire and a liquid, we have the end *916of a wire and some compressible solid material, like plumbago, in constant contact, it is equally clear that by varying the pressure on the wire the resistance will be varied, and consequently the strength of the current. Here variation of pressure may be said to vary the resistance by varying the compression of the mass of material rather than by varying the intimacy of contact or area of contact.
Turning now to the telephony transmitter art, we find that none of these ways of varying resistance by varying pressure has advanced the art or made any impression upon it. These ways of varying resistance, and the difference between them, have been brought out and emphasized by the learned and skilled experts in the case at bar. These ways are simply the different modes of operation of the materials which compose the electrodes. They certainly cannot form the basis for any method patent covering all materials whose mode of operation is the same, because there is nothing in the so-called area varying method, or density varying method, or intimacy of contact varying method, considered by themselves and apart from the discovery of microphonic action, or the special properties of some material like carbon, which has ever contributed anything to the progress of the telephonic art.
The terms “pressure” and “variation of pressure,” considered by themselves, are mere abstractions, and cannot involve invention. There may be instances, however, where an invention may be said to reside in the discovery of “pressure,” or “variation of pressure,” and their utilization in the telephonic art. For instance, Edison may have discovered that carbon or plumbago varied its resistance greatly under pressure; and, if this discovery were embodied in a telephone transmitter, the invention might be said to reside in his discovery of “pressure,” or “variation of pressure,” in a particular material. Again, some one might have discovered that the resistance varies enormously with pressure at a loose contact between electrodes; and, if this discovery were embodied in a telephone transmitter, the invention might be said to reside in the discovery of pressure, or variation of pressure at a loose contact. It cannot be said, however, that Berliner made any discovery of pressure or variation of pressure, which has proved of any utility in the art. His discovery, as we have seen, of the variation of pressure at a point of contact between metallic electrodes in a telephone transmitter possessed little utility and was practically worthless. It may have been an invention, in that he discovered that the minute vibrations of the diaphragm due to sound waves, by varying the pressure at the contact between metallic electrodes, as distinguished from other kinds of electrodes, vary the resistance and reproduce sound; but this is the limit of his invention, in the absence of any discovery of microphonic action springing from loose contact between the electrodes.
To summarize our conclusions respecting the variable resistance transmitter:
We find that Bell, in March, 1876, discovered that the minute atmospheric vibrations due to sound waves would cause the diaphragm to vibrate, which vibrations, by varying the pressure between a solid electrode and a liquid electrode in constant contact, produced *917variations of electrical resistance, whereby speech may be transmitted.
We find that Edison, in February, 1877, discovered that the minute atmospheric vibrations due to sound waves would cause the diaphragm to vibrate, which vibrations, by varying the pressure between two solid electrodes of different conductivity in constant contact, one metallic and the other hard rubber covered with a plumbago film, produced variations of electrical resistance, whereby speech may be transmitted.
We find that Edison, on April 1, 1877, discovered that the minute atmospheric vibrations due to sound waves would cause the diaphragm to vibrate, which vibrations, by varying the pressure between two solid electrodes in constant contact, one metallic and the other compressible plumbago, produced variations of electrical resistance, whereby speech may be transmitted.
We find that Berliner, on April 14, 1877, discovered that, the minute atmospheric vibrations due to sound waves would cause the diaphragm to vibrate, which vibrations, by varying the pressure at the point of contact between metallic electrodes in constant contact, produced variations of electrical resistance, whereby speech may be transmitted.
All of these discoveries, when embodied in transmitters, were, inventions, but none of them was a commercial instrument, or solved the problem of a practical long-distance speech transmitter.
We find that, in the fall of 1877, Edison discovered the carbon electrode; that this discovery represents the first marked advance in the transmitter art since the 1876 Bell patent; and that the carbon electrode is found in every commercial battery transmitter.
We find that in May, 1878, Prof. Hughes discovered microphonic action, or the fact that sound waves produce remarkable variations of resistance at a loose or feeble contact between solid electrodes in constant contact, whereby speech may be transmitted; that the principle he then made known is utilized in every practical battery transmitter; and that he embodied his discovery in an instrument which he was the first to term a microphone.
We also find that Edison’s discovery of the carbon electrode and Hughes’ discovery of microphonic action solved the problem of a variable resistance transmitter, whereby speech may be transmitted long distances, and that both these discoveries are embodied in the defendants’ transmitters.
We also find that the two claims of the Berliner patent in suit, although upon their face open to the objection of excessive breadth, may be sustained when read in connection with the specification, provided they are limited to metallic electrodes, and that, when so limited, the defendants’ transmitters do not infringe.
Our conclusion is that the decree of the circuit court must be affirmed on the ground of noninfringement.
The decree of the circuit court is affirmed, with costs for the appellees.