In the preceding appendices it has been demonstrated that all that is essential in both transmitter and receiver of a Telephonic system was to be found existing in 1863 in the Telephone of Reis. There yet remains to be met the doctrinaire objection that as Reis never explicitly mentions an undulatory current as distinguished from an intermittent one, he never intended to use such a current. This objection is advanced only by those persons who have committed themselves to the idea that speech cannot be transmitted by a transmitter which opens and closes the circuit.
It is certain that Reis did not in any of his writings explicitly name an undulatory current: but it is equally certain that, whether he mentioned it or not, he both used one and intended to use one. He did not concern himself as to the precise manner in which the current fluctuated provided only he attained the end in view—namely, that the vibrations of the armature of the receiver should be similar to those of the transmitter. This he did lay down with great clearness and emphasis as his guiding principle; and he cared not about the intermediate question as to how the current did the work. He told the world that the electromagnet at the receiving end must be magnetised and demagnetised correspondingly with the vibrations imparted by the air to the tympanum of his transmitter, in order that the armature might be set into vibrations similar to those of the speaker’s voice. If the tympanum of the transmitter vibrated or oscillated or undulated—the terms are synonymous—so must the armature of the receiver. Graham Bell has told us precisely the same thing: “The current traversing the coils of the electromagnet E occasions an increase and diminution in its intensity” [that is to say, magnetises and demagnetises it], “and the armature A1 is thrown into vibration” ... “and thus imparts to the air at n1 a facsimile copy of the motion of the air that acted upon the membrane n.” Bell agrees then absolutely in every detail with what Reis said on this point. That sound-waves should be transmitted by a Telephone requires indeed a process of several stages. (1.) The sound-waves must strike upon the tympanum of the transmitter and make it undulate, or, oscillate, or vibrate—whichever term you please—in a corresponding manner. (2.) The undulating tympanum must act upon the circuit, and either itself induce undulating or vibrating currents (Bell’s plan, by magnetic induction), or else throw a current already flowing there, into undulations, or vibrations, or oscillations (Reis’s plan, by varying contact-resistance), but in either case these undulations of the current must correspond to the original undulations of the air-waves. (3.) The undulating, or vibrating, or oscillating current must run round the coils of the electromagnet and cause its magnetic force to undulate, or oscillate, or vibrate by demagnetising it and then magnetising it, but this also must be in a manner corresponding to the original undulations. (4.) Further, the armature of the receiver must be set into undulations, or vibrations, or oscillations corresponding to those of the force of the electromagnet, and therefore to the undulations of the current that is magnetising and demagnetising it, and therefore identically corresponding with the original undulations of the sound-waves. (5.) The armature must communicate its vibrations to the air and to the ear of the listener. Of these successive stages Reis explicitly told the world that his instrument was to do the first one and the last three, and he several times emphasized the statement, that the final undulations of the last stage were to be similar to the original undulations of the first stage. The air at the listening end, the armature of the receiver, and the magnetism of the magnet, were all to be set by the fluctuations of the current into undulations corresponding with those of the tympanum at the speaker’s end, and of the waves of his voice. It is perfectly clear therefore, that he regarded as self-evident the intermediate stage, and he did not dwell upon the necessity of the point, that his transmitting-current must also vibrate, because this was obviously so, and was only an intermediate matter of secondary moment. He chose rather to point out the necessity of unification between the first and last stages, leaving it to common sense to see that the “interruption” or the “opening and closing” of the circuit must be effected in a manner corresponding to the undulations of the impressed sound-wave. Had the “interruptions” not been of the nature of corresponding variations of contact, the current could not have been set into corresponding vibrations, and the armature of the electromagnet could not have reproduced the vibrations of the transmitter. Clearly Reis’s whole conception of telephony included as a minor and intermediate step the fact that the current was, by the action of the transmitter, caused to vary in strength in correspondence with the undulations of the tympanum—that, in fact, it was made to undulate by the action of the tympanum and of the interruptor which opened and closed the circuit in obedience to the undulations of the tympanum and in proportion to them.
A difficulty has been raised by telegraph operators that opening and closing the circuit means opening and closing the circuit in abrupt alternations of make-and-break. Reis never said so. Reis never used the phrase in this restricted and technical sense. He was not a professional telegraphist, and, as pointed out in Appendix I., he so arranged his contacts with the following springs and other contrivances, that the “opening and closing” of the circuit should not and could not be abrupt. A Reis transmitter is no more a “make-and-break” instrument than the Blake transmitter is. Both will give undulatory currents by opening and closing the circuit to a greater or less degree, if spoken gently to. Both will give abrupt makes-and-breaks of the circuit if shouted to, in spite of the following-springs, which are used to prevent abrupt interruptions. The term “opening and closing” which Reis applied to his transmitter, is used by him in exactly the same way as the phrase is used by engineers in describing the action of the governing throttle-valve of a steam-engine. The function of the governor, we are told in treatises on engineering, is to open and close the throttle-valve in a manner corresponding to the fall or rise of the governor-balls. No one in his senses imagines that the opening and closing action here referred to means an absolutely abrupt intermittence in the supply of steam. If the governor-balls rise a little by increase of speed, there is a corresponding closing, proportionate in amount to the amount of rise. If any person were to impress an oscillatory motion of rise and fall upon the governor, the supply of steam would be thrown into corresponding undulations. The matter stands precisely so with Reis’s “interruptor” or “regulator;” it opens and closes the circuit in a manner corresponding with the undulations communicated to it. If it did not, it would violate the principle of correspondence so emphatically laid down by Reis.
It is, however, true that Reis’s instruments, in spite of springs and adjusting screws, and other devices to prevent abrupt make-and-break occurring, were prone, by reason of the very lightness of the parts, to break contact, if too loudly spoken to. They share this fault with the more perfect transmitters of Blake and Berliner which are used to-day so generally. The undulatory currents of these transmitters are, like those of Reis’s transmitters, liable to an occasional abrupt interruption, which, though it may not seriously affect the intelligibility of the words, does, to some extent, mar the perfection of the articulation. Still, in practice, to judge by the instruments used in the telephone exchanges of Great Britain, the Blake transmitter with its liability to make-and-brake abruptly is a more satisfactory instrument than the Bell transmitter, which is not used at all. Now the Bell transmitter working on the principle of which Bell is the first and undisputed inventor, is one in which the degree of contact in the circuit is never changed: for it works by the principle of “induction,” whereby currents are set up in a circuit that is never opened or closed, either partially or wholly. Nevertheless the Blake transmitter, which opens and closes the circuit in proportion to the undulations of the tympanum, is the more satisfactory instrument for producing the undulating currents required to procure the all-essential correspondence between the undulations of the tympanum of the transmitter and those of the armature of the receiver. To sum the matter up, it appears that an instrument which opens and closes the circuit on Reis’s principle of transmitting is in practice a more satisfactory transmitter of undulatory currents than Bell’s transmitter which cannot open or close the circuit in the least. Reis, with his instruments, transmitted speech—as Herr Hold tells us (p. 126)—when the words spoken were not too loud. That is a proof that he did really use, whether he knew it or not, undulatory currents of electricity: and an undulatory current is none the less an undulatory current, even if occasionally abruptly interrupted. A speech is none the less a speech, even if the orator sneeze once or twice while speaking. Nay, we may go further, and say that an undulatory current is an undulatory current, even though the finer ripples of the waves are lost in transmission. This is what seems to have been the case with Reis’s instruments as they were in 1861 and 1862. The consonants were satisfactorily transmitted, and so were all musical tones within the range of the instrument. But the finer ripples of the vowels were lost somehow in transmission. Reis, whose innate honour and modesty led him always rather to understate than overstate the facts, most frankly acknowledged this, nay even invited attention to the fact, and discussed the imperfection from a high scientific standpoint. He proposed to rely for the correctness of his views upon the actual recorded curves of sound-waves, as taken down automatically by the then newly-invented phonautograph of Scott (see p. 60). It is perfectly marvellous how precise his views were upon the correspondence between the graphic curve or wave-form of a sound and the actual sound itself; a precision amply justified by the experience and the discoveries of the last ten years.
This matter of representing sounds—or rather the varying density of the air in the sound-wave—by a graphic curve, was a vital one to Reis. Had he had a less clear view of the nature of sound-waves than that afforded by a graphic curve, I doubt whether he would ever have grasped the problem of the telephone—that the final vibrations, or undulations, or oscillations of the armature in the receiver must correspond with—must be the very counterpart of—those of the tympanum of the transmitter. The clearness with which Reis saw this is only surpassed by the clearness with which he expressed himself upon it. For him a sound was simply a complicated series of variations in the density of the air, and capable, in all its complexity, of being represented by the rise and fall of an undulatory curve. “Every tone, and every combination of tones, evokes in our ear vibrations ... the motions of which may be represented by a curve” (p. 54). “That which is perceived by the auditory nerve ... may be represented graphically according to its duration and magnitude by a curve” ... (p. 53). “Our ear can perceive absolutely nothing more than is capable of being represented by similar curves” (p. 53). The curves with which he accompanied his original memoir—and now reproduced in facsimile, from Legat’s plates, at the end of this volume—are evidence of the thoroughness of his grasp on the undulatory principle. And he explicitly states this principle amongst “the various requisite conditions which must be fulfilled by the transmitting and receiving apparatus for the solution of the problem that has been set” (Legat’s Report, p. 71). He declared that so soon as it should become possible “at any place, and in any prescribed manner” (that is to say, whether by electric undulations or by mechanical undulations, as in the string of the toy telephone, or by any other means), “to set up vibrations whose curves are like those of any given tone or combination of tones,” we should then receive the same impression as that tone or combination of tones would have produced upon us.
So much for Reis’s principle of correspondence of undulations between the transmitter and the receiver; we have seen how clear and precise, yet how comprehensive it was, and how the general proposition necessarily included within itself, as an intermediate step, the particular minor proposition that the undulations of the current must also be in correspondence with the voice.
Keeping these points in mind, it is very remarkable that when Graham Bell, fourteen years later, followed Reis “into the field of telephonic research,” he selected the very same method of expressing the relations between sounds and the undulations which corresponded with them. To show how remarkably in agreement the views of Reis and Bell are upon this question of representing by a curve the undulations which correspond to the voice, we select the following paragraphs and place them in parallel columns.
The very remarkable agreement of the preceding passages receives a most striking confirmation by comparing the curves respectively drawn by Reis and by Bell. These are facsimiled below, Reis’s “combination”-curve ([Fig. 47]) from Plate I. of his Memoir (also [Plate I.] of this volume), and Bell’s “resultant”-curve ([Fig. 48]) from Fig. 4 of his United States Patent Specification No. 174,465.
The most casual observer cannot fail to notice here that the three lines of undulatory curves of Bell’s specification are practically identical with the three lower lines of undulatory curves of Reis’s memoir. They are, moreover, in each case introduced for the sake of showing how a complex curve corresponds to a compound undulation.