microphonic 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, C, terminating the screw-threaded rod, B, which is supported by the bar or stand, d. The pressure of the ball, C, 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

mitter 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 of 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 'one 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 would 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 microphonic action. When the ends were pressed together with considerable pressure, he had not discovered microphonic 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

accustomed 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 voice was wanting; but in the following experiments the 'timbre' became more and more perfect, until it reached a perfection leaving

nothing 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:

In 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 conductibility; 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