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

appear 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 not 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

the 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 conception, 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

full 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 manner."

The drawing of the transmitter is here reproduced:

Figl

"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, C, 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 microphonic action.

Referring to the figure, Berliner says:

"Against the plate, and touching it, is the metal ball, C, 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 the plate vibrate [by sound waves] the pressure at the 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