Any one who compares together the many different forms of Reis’s Transmitters cannot fail to notice that amidst the great variety of form, two essential points are preserved throughout, the presence of which is fundamental. These two essentials are, firstly, the tympanum to collect the voice-waves, and, secondly, an electric mechanism, consisting of two or more parts in loose or imperfect contact with each other, and so arranged in combination with the tympanum that the motions of the latter should alter the degree of contact, and consequently interrupt, to a greater or less degree, the current of electricity flowing between the contact-pieces. It was of course familiar to all electricians, long before Reis, that a bad, or imperfect, or loose contact in a circuit offered a resistance and interrupted the flow of an electric current. In all ordinary telegraphic and electric apparatus great care was taken to avoid loose and imperfect contacts by using clamping-screws and solid connectors. But Reis, having made up his mind (see p. 77) that the action due to the magnetising current must vary in a manner corresponding with, and therefore proportional to, the vibrations of the voice, utilised this property of imperfect contacts which alter their resistance according to the degree of contact, by arranging his mechanism so as to apply the voice to vary the degree of contact. This was the essence of his transmitters. In other words, he applied the voice to control or moderate the strength of the current generated by a battery. His “interruptors” may therefore with propriety be called “electric current contact regulators;” and put into technical language, the essence of this part of his invention lay in the combination with a tympanum of electric current regulators working upon the principle of variable contact.
In another appendix is discussed the precise nature of that which occurs at a point of variable or imperfect contact, and which results in a corresponding change of electrical resistance when the degree of contact is varied. Suffice it to say here that it is impossible to vary the degree of contact between two bodies which are lightly pressing one against the other, and through which an electric current is flowing, without altering the resistance offered to the current by this joint in the circuit. If the two surfaces are pressed together, so that there is a good contact, the current flows more freely, finding less resistance. If, on the other hand, by altering the pressure or the amount of surface exposed, we change the degree of contact and cause fewer atoms of one piece to touch those of the other piece, the current meets with greater obstruction and cannot flow with such strength as before: it is partially “interrupted,” to use the expressive term employed by Reis.
Now this operation of varying the degree of pressure in order to vary the resistance of the interrupter or contact regulator, was distinctly contemplated by Reis. We find his definite instructions, for example (see p. 75), for arranging the relative lengths of the two parts of the curved lever in one of his transmitters, so that the movement of one contact-piece may act on the other contact-piece with the greatest possible force; in other words, he shortened his lever at the working end, sacrificing its range of motion in order to get a greater range of pressure at the contact-point.
It has often been said, but incorrectly, that Reis intended his “interruptors” or contact regulators to make and break the electric circuit abruptly in the manner of a telegraphic key worked by hand. No doubt in the mouth of a professional telegraph operator the words “interrupting” the circuit, and “opening” and “closing” the circuit, do now-a-days receive this narrow technical meaning. But Reis was not a professional telegraph operator: he did not (see p. 87) even know the signals of the Morse code, and it is self-evident that he did not use the terms in any such restricted or unnatural sense as abrupt “make-and-break,” because he proposed at the outset to interrupt the current in a manner represented by the gradual rise and fall of a curve, stating emphatically in his very first memoir on telephony (p. 55), that to reproduce any tone or combination of tones all that was necessary was “to set up vibrations whose curves are like those” of the given tone or combination of tones. Moreover, in the construction of almost all his transmitters, even in the very first—the model of the human ear—he purposely introduced certain parts which could have no other effect than to prevent the occurrence of complete breaks in the continuity of the current. In fact, instead of using rigid supports for his interruptor, he mounted one or both of the contact-parts with springs, so that one should follow the movement of the other with a gentle pressure never amounting to absolute break, except perhaps in the accidental case of a too loud shout. By employing these following-springs, he introduced, in fact the element of elasticity into his interruptor; and clearly he introduced it for the very purpose of avoiding abrupt breaking of the contact. In the first form Fig. 5, p. 16 (the “ear”), there was one spring; in the fourth form, Figs. 9 and 10, p. 21 (the “bored block”), there were two springs, one of steel, curved, and one, a straight but springy strip, of copper; in the eighth form (the “lever” form), Fig. 14, p. 25, there were two springs; in the ninth form, Fig. 15, p. 26, there was a springy strip of brass. In the final form, Figs. 17 and 18, p. 27 (the “square-box” pattern), there was, it is true, a springy strip of copper, but the light adjustment of contact was in this form obtained, not by a spring, but by the inertia of the upper contact-piece which by its own weight pressed gently upon the lower contact-piece. In every one of these forms, except the last, there was moreover an adjusting-screw to determine the exact degree of initial pressure between the contact surfaces. Doubtless the difficulty of adjusting this screw to give the exact degree of contact, enhanced as that difficulty was in consequence of the liability of the membraneous tympanum to become flaccid by the moisture of the breath, induced Reis to think that the later form of the apparatus in which this adjustment was no longer retained would be more easy to use, or, as he says in his Prospectus, more accessible to others. Yet undoubtedly the absence of the spring at the contacts led some persons to fancy that the instrument was intended to be shouted or sung to so loudly that every vibration should make the upper contact-piece jump up from the lower, and as Professor Müller even suggests (p. 98), produce a spark! But such a manner of using the instrument would entirely defeat Reis’s most fundamental principle, that the interruptions should be such as to correspond to the undulating curve which represents the pressure due to vibration of the sound-wave; the possibility of representing the degree of pressure by a curve being one of the two principles set forth in his paper “on Telephony” (p. 55), in which he remarks, that “Taking my stand on the preceding principles, I have succeeded in constructing an apparatus by means of which I am in a position to reproduce ... even to a certain degree the human voice.” Reis was perfectly well aware, as his curves show, that a complicated sound-wave does not consist invariably of one condensation followed by one rarefaction, but that there are all sorts of degrees of condensation which may follow one another, and all capable of being represented by a curve. If all sounds consisted of one rarefaction following immediately after each one condensation there might be some propriety in proposing that after each “make” of contact there should be a “break” in the sense of an abrupt or complete breach in the continuity of the current. But, obviously, the fact that one condensation may follow another without a rarefaction between (which Reis’s curves show that he knew) must be amply sufficient to prove that on Reis’s own principle his interruptor was meant to produce variations in the degree of contact in exact correspondence with the variations in the degree of pressure, whatever these might be. Had he not meant this, he could not have talked about “taking his stand” on the principle of representing varying pressures by an undulatory curve. Now, from what has been adduced, the following points are clear:—
Firstly, that the contact-regulator which Reis combined with the tympanum was meant to interrupt the current, more or less, according to the varying movements imparted to it by the voice.
Secondly, that Reis intended such interruptions or variations of contact to be proportional to, or to “correspond” with, the variations indicated by the undulatory curve of varying pressures.
Thirdly, that for the purpose of preventing the occurrence of abrupt breaks in the continuity of the circuit, he used springs and adjusting screws, and in one form availed himself of the inertia of the moving parts to attain a similar end.
It is also clear from his own prospectus, that he was aware that for the simpler and ruder purpose of transmitting musical airs, in which the number of the vibrations is the only consideration and where each single condensation is actually followed by a rarefaction, actual abrupt breaks in the continuity of the circuit are admissible. Reis chose this simple case as the one capable of being readily grasped by a general audience, though it was obviously only a partial explanation of the action of the apparatus in the simplest case that could be presented.
Turning now to some of the more modern transmitters, we will inquire how far Reis’s fundamental principles are involved in their construction. We will first take Berliner’s transmitter, of which Fig. 43 is a drawing, reproduced from the sketch in the specification of his British Patent. This transmitter consists of a tympanum of thin metal to collect the sound-waves, and behind it is attached an interrupter or current regulator, identical in almost every respect with that of Reis. One of the contact-pieces, marked E, circular in form, is fixed to the centre of the tympanum, and vibrates with it, precisely as in Reis’s latest, and in some also of his earlier instruments. Against this there rests in light contact a second contact-piece, in the form of a small blunt spike, F, screwed into a short arm, loosely jointed to the part N, where the circuit is connected. As in Reis’s latest transmitter (Fig. 17, p. 27), so here, the contact-pieces are kept in contact by gravity. When any person talks to the tympanum it vibrates, and, as a result, the degree of contact between the two surfaces is varied, resulting in a greater or less interruption of the current, the inertia of the upper contact-piece, serving to prevent complete abrupt “break” of the circuit, except under unusually strong vibrations. In fact, if the speaker talks too loudly when speaking into Berliner’s transmitter, he will cause abrupt breaks to occur instead of partial interruptions; and a rattling noise comes in to confuse the speech at the receiving end of the line. But this is precisely what occurs in a Reis’s transmitter if one talks too loudly to it. It is obvious that if Berliner’s transmitter is a “make-and-break” instrument, so is Reis’s, because the principle of action is identical: and it is also obvious that if Berliner’s instrument is capable of varying the resistance at the contact-points by interrupting the current in a manner corresponding to the pressures of the air in the sound-waves, so also is Reis’s instrument.
It is a fact that in Berliner’s instrument it is usual to make the contact-pieces, or one of them, of hard artificial coke-carbon, as this substance will neither fuse nor rust. But Berliner’s transmitter will transmit speech perfectly if the contact parts be of brass, silver, platinum, carbon, or almost any other good conductor. In most of Reis’s instruments the contact-pieces were usually of platinum; but they work quite as well if artificial coke-carbon is substituted. In fact, Reis’s principle of variable and elastic contact is applicable to contact-pieces of any material that is a good enough conductor of electricity and hard enough for the purpose. The main improvement in Berliner’s transmitter is the substitution of the metal tympanum for the membraneous one, which was liable to become flabby with moisture.
We pass on to Blake’s transmitter, which is the one more generally used in Great Britain than any other. The drawing, Fig. 44, of this instrument is taken from the specifications of Blake’s British Patent, and shews all that concerns the contact-parts. It does not show the accessories, the induction-coil, or the form of adjusting screw and frame peculiar to this instrument. Inspection of the figure shows that this transmitter consists of a mouthpiece in the form of a conical hole bored through a stout plank of wood, and closed at the back by a metal tympanum of exactly the same size as that of Reis, behind which the interruptor is placed, precisely as in some of Reis’s instruments. In this interruptor both the contact-parts are supported on springs, resembling, even in the curve given to them, the springs Reis used. The first of the contact-pieces is a small metal spike. Concerning it Mr. Blake remarks (page 4 of Specification):—“It is desirable that it should be formed of, or plated with, some metal, like platinum or nickel, which is not easily corroded. It may be attached directly to the diaphragm, but I prefer to support it independently, as shewn, upon a light spring.” ... “This method of supporting the electrode ensures its contact with the other electrode under some circumstances when otherwise they would be liable to be separated and the circuit broken.” In fact this spring serves functions precisely identical with those of the springs used by Reis. The second of the contact-pieces may be described as a mass of metal at the end of a spring. Of it the patentee remarks:—“This weight may be of metal which may serve directly as the electrode, but I have obtained better results by applying to it, at the point of contact with the other electrode, a piece of gas-coke or a hard-pressed block of carbon.” As a matter of fact, a mass of silver or of nickel or of platinum will transmit talking perfectly, but these metals, though better conductors, are more liable to corrode and fuse, and may require therefore more frequent renewal, than gas-coke. Since, then, it is immaterial to the action of a Blake transmitter what substance is used for the contact-pieces, it is clear that the principle of employing an interruptor mounted on springs is the real feature of the instrument. Reis also mounted his interrupters with springs, and for the very same purpose. The function of the weight on the second spring of the Blake transmitter is to resist the movement of the tympanum, and to “modify by its inertia the variations of pressure” between the two contact-pieces. In other words, it acts partly as Berliner’s transmitter, by inertia. So did one of Reis’s instruments, as we have seen. In the Blake instrument there is the happy idea of applying both the spring-principle and the inertia-principle at once. Yet, in spite of this, if the speaker shouts too loudly into a Blake transmitter, he will cause abrupt breaks between the contact-pieces instead of producing partial interruptions in the contact, and in that case speech will, as heard at the other end of the line, be spoiled by a rattling noise. It is possible, also, with Reis’s instruments to spoil the articulation by shouting too loudly, and causing actual abrupt breaks in the continuity. If Blake’s interruptor can be worked as a make-and-break in this sense, so can Reis’s: for there is not one of the features which is essential to Blake’s instrument that cannot be found in Reis’s also.
By way of further carrying out the comparison between Reis’s methods of combining his tympanum with his contact-regulator, and the methods adopted by later inventors, we give, in Fig. 45, ten comparative sketches, the first five of which illustrate Reis’s methods. In these sketches the only liberty taken is that of representing no more of the instruments than the actual parts wanted in the comparison. No. 1 represents the working-parts of Reis’s first model ear, with its curved lever, platinum-tipped spring, and adjusting screw. No. 2 shows the springs, screw, and contact-pieces of Reis’s bored-block transmitter (“fourth form:” compare Figs 9 and 10, p. 21). No. 3 shows the curved lever, the springs, and the adjusting screw of Reis’s eighth transmitter (“lever” form). No. 4 gives the working parts of Reis’s ninth transmitter, described in detail on p. 27. No. 5, in which the tympanum is placed in a vertical position, merely for convenience of comparison with the other figures, shows the working parts of Reis’s final form of instrument, in which gravity and the inertia of the upper contact-piece enabled him to dispense with the adjustment of spring and screw. No. 6 shows in profile Berliner’s transmitter, which may be instructively compared with No. 5. No. 7 shows the working part of Blake’s transmitter, which should be compared with Nos. 2 and 4: even the curve of the springs imitates that adopted by Reis. Nos. 8, 9, and 10 are forms of transmitter devised by Edison. No. 8 is copied from Fig. 10 of the specification of Edison’s British Patent. It will be seen that here there is an interruptor placed on each side of the tympanum, and that each interruptor consists of a short spike mounted on a spring and furnished with an adjusting-screw. “Platina foil disks,” says the inventor, are to be secured to each side of the diaphragm, and against these disks, as in Reis’s instruments, press the contact-points of the interruptors. The patentee also states (p. 7 of his Specification), that for these contact-points “any substance not liable to rapid decomposition” may be used. This term includes all the substances used by Reis, and a great many others. It will therefore be seen that this whole device is nothing more than a Reis transmitter with the contact parts duplicated. Yet this instrument was intended by Edison to transmit speech, and will, like Reis’s instrument, transmit speech if properly used. No. 9 of the set of sketches is taken from Fig. 25 of Edison’s British Specification, but omits the induction-coil and other accessories, retaining the parts wanted for comparison. The patentee thus describes the parts figured. “The tension-regulator [meaning thereby the interruptor or contact-regulator] is made of platina-foil upon the surface of two soft rubber tubes; one on the diaphragm, the other on the adjusting-screw.” It is interesting to note here how the ingenuity of the later inventor led him to vary the construction adopted by the original inventor in substituting an elastic cushion of soft rubber for the springs of the older instruments. But the principle of combining a tympanum with a contact-regulator, which was Reis’s fundamental notion, is here also the leading idea; and the further idea of obviating abrupt breaks in the current by applying elastic supports is also carried out. Edison even copies Reis in having an adjusting-screw, and he applies the very same substance—platinum foil—which Reis used in his very first and his very last transmitter. Edison’s transmitter transmits speech very fairly, even without any of such later accessories as induction-coils; and why should it not? It is constructed on the very lines, nay, with details almost identical with those prescribed by Reis in describing his invention. It embodies those fundamental ideas which Reis set before him when he said, “Taking my stand upon the preceding principles, I have succeeded.”
The last of the ten sketches of Fig. 45 is taken from Edison’s first American Patent specification [No. 203,014, filed July 20, 1877], and shows a duplicated interrupter with springs and adjusting-screws combined with a tympanum. Further comment on this arrangement is needless, save to remark that in this patent for “speaking telegraphs,” Edison himself describes the contact-apparatus which Reis termed an “interrupter,” as a “circuit-closer,” or in another place as “circuit-breaking connections,” and, in his British Patent quoted above, as a “tension-regulator.” It is evident that if Reis could transmit speech by an interrupter which closed and opened the circuit (always in proportion to the vibrations) there is no reason why Edison seventeen years afterwards should not accomplish the same result by a similar means. But it has lately been fashionable to deny that any such device as an interrupter mounted on springs can transmit speech at all!
We have now compared with Reis’s transmitters several of the more modern inventions. It would be possible to carry comparison further were that course needed. We have not thought it worth while to rake up Edison’s now discarded lamp-black button transmitter; and we have not yet spoken of Crossley’s transmitter nor of Theiler’s transmitter, nor of their parent the Hughes’ microphone, nor of dozens of other forms. In some of these there is no specific “tympanum,” but only a sounding-board of pine-wood, and in most of them the points of loose-contact, where interruption more or less complete may occur, are multiplied. But they all come back in the end to Reis’s fundamental idea, namely that of setting the voice to vary the degree of contact in a mechanism which he called an interruptor, and which others have called a current-regulator (or, less correctly, a tension-regulator) which, because the degree of contact between its parts was varied, caused those parts to offer more or less resistance to the flow of the current, and thereby threw it into vibrations corresponding to those of the sound-wave impressed upon the tympanum. There is not a practical transmitter used in any of the telephone exchanges of Great Britain to-day that does not embody this principle.
Reis did, indeed, penetrate to the very heart the principles necessary to be observed in a successful telephone. He was master of the situation. For, as in every practical transmitter in use to-day, so in his transmitter, there was a loose contact in the circuit so arranged that the voice could act upon it, and thereby regulate the strength of the current. If you eliminate this part of the apparatus,—screw up the loose-contacts of your transmitters, so that your voices cannot affect them,—what will your telephones be worth? No: the essential principle of the transmitter—“Das Telephon” emphatically as its inventor styled it—is variable contact; and that all-essential principle was invented and applied for the purpose of transmitting speech by Philipp Reis in 1861.
If this does not suffice as a claim for the invention of the Telephone transmitter, it may well be wondered what will. We can dispense with all other features save this one. We can even dispense with the tympanum or diaphragm which Reis introduced, and can operate on the contact-parts without the intervention of this part of the combination. We can use the very metals which Reis used, and dispense with lamp-black and all the fallacious rubbish that has been subsequently devised about semi-conductors, whatever that term may mean. We can even dispense with springs and adjusting screws. But with the principle of variable contact we can not dispense. That which alone is indispensable Philipp Reis discovered.