Philipp Reis: Inventor of the Telephone / A Biographical Sketch

by Silvanus P. Thompson

For the better comparison of Reis’s electro-magnetic receiver with those of more modern date, we here present in [Fig. 46] a comparative view of a number of different forms of receiver in which Reis’s principle of causing an electro-magnet to set up vibrations in an armature is applied. In this set of figures, A and B are the suggested forms mentioned in the letter of Mr. Horkheimer, p. 119, and show an electro-magnet, opposite the poles of which is placed an armature (a bar) which must be of iron or other metal capable of having magnetism induced in it, and which, by reason of its attachment to an elastic spring, is capable of being made to oscillate to and fro when attracted with a varying force. Reis clearly recognised the necessity of further providing a sufficient resounding surface by means of which the surrounding air could be set in motion: for in the case of these two suggestions the electro-magnet and its elastically-mounted armature were placed within a cigar box. C is a plan of the receiving instrument previously described and figured in Plate II. and in figures 21 and 34 on pages 32 and 109. In this instrument the electro-magnet was horizontal, the armature, a bar of iron of oval section (which in the original drawing in plate II. appears to have been in reality a hollow bar or tube) attached to a thin lever described as a plank, pivoted like a pendulum to an upright support, but prevented by a set-screw and a controlling spring from vibrating in the manner of a pendulum. Such an arrangement, in fact, vibrates in perfect correspondence with any vibrations that may be forced upon it by the electro-magnet. The broad flat surface of the lever—he specially directed that it should be broad and light—transfers the vibrations to the air, and is aided by the surface of the sounding-board on which the apparatus stands. This apparatus has, therefore, all the elements of a successful receiver, except only that its shape renders it inconvenient for portability. But by reason, firstly of its armature of iron, secondly of the elastic mounting of that armature, thirdly of the extended surface presented, it is admirably adapted to serve as an instrument for reproducing speech.

Fig. 46.

[Fig. 46] D represents the excellent electro-magnetic receiver devised in 1865 by Yeates (compare [Fig. 42], p. 128) to work with the Reis transmitter, and is in many respects identical with the preceding form. The armature, a strip of iron, was attached at one end by a very stiff steel spring to a pine-wood sounding-board over a hollow box, from the base of which rose the metal pillar which supported the electro-magnet. This receiver also contains all the elements of a successful receiver, the armature being of a material capable of inductive action, and elastically supported; whilst the sound-box provided adequate surface to communicate the vibrations to the air.

We now come to the more modern instruments of Gray, Bell, and Edison. So far the receivers of Reis and of Yeates were intended for reproducing any sound; but now for the first time, ten years after the date of these early telephonic receivers, we meet with instruments devised with the express purpose of receiving only certain selected tones.

For the purposes of multiple acoustic telegraphy, that is to say for the purpose of signalling the “dots” and “dashes” of the Morse code in a number of different fixed musical notes, each of which is to be signalled out and repeated by a receiver adapted to vibrate in that note alone, it is clear that the instruments of Reis, adapted as they were to transmit and receive any sound that a human ear can hear, would not answer. Accordingly those experimenters, who from about the year 1873 to the year 1870, applied themselves to multiple telegraphy—foremost amongst them being Mr. Elisha Gray and Prof. Graham Bell—dropped the use of the tympanum in the transmitter and devised new transmitters and new receivers, in most of which the ruling idea was that of employing a vibrating tongue or reed, tuned up to one particular note. Now it is obvious that a receiver which, like those of Reis, is adapted to receive any tone, can also receive a musical note. But for the operation of “selective” reception, a receiver must be employed, not only tuned to one note, but tuned to the very note emitted by the particular transmitter with which it is to be in correspondence. Elisha Gray found this out very early in his researches. In the winter of 1873-4[49] he was transmitting musical tones by a sort of tuning-fork interruptor, and received them on an instrument shown in [Fig. 46] E, which represents a form of electro-magnet mounted for the purpose. It was “a common electro-magnet, having a bar of iron rigidly fixed at one pole, which extends across the other pole, but does not touch it by about one sixty-fourth part of an inch. In the middle of this armature a short post is fastened, and the whole is mounted on a box made of thin pine, with openings for acoustic effects.” It was, in fact, very similar to Yeates’s receiver just described, and Gray found it capable of receiving not only simple musical tones but composite tones, and even harmonies and discords. In fact, like Reis’s and Yeates’s receivers, it could receive anything that the transmitter sent to it, even including speech. Now this did not suit Gray, who wished to have selective receivers, one to take up note A, another note C, &c. Accordingly in 1870 we find Gray taking out a fresh patent[50] for selective receivers, which he also called harmonic analysers, each of which consisted of “a tuned bar or reed suitably attached to an electro-magnet, and the whole mounted upon a resonant box.” [Fig. 46] F is reproduced from Gray’s British patent. “A vibrating tongue reed, or bar” of steel “is united with one pole of the magnet. The free end of the reed passes close to, but does not touch the other pole of the magnet.” Gray further says that the reed is made with parallel sides and tuned by cutting it away at one point, as this mode prevents false nodal vibrations from occurring.

Selective receivers for multiple telegraphy were also invented by Graham Bell. The form shown in [Fig. 46] I is transcribed from Fig. 15 of Bell’s Specification to his British Patent, No. 4765, of the year 1876 (dated 9th December), which the inventor thus describes: “It is preferable to employ for this purpose an electro-magnet E, Fig. 15, having a coil upon only one of its legs. A steel spring armature A is firmly clamped by one extremity to the uncovered leg h of the magnet, and its free end is allowed to project above the pole of the covered leg.” In fact the arrangement was almost identical with, but not quite as good mechanically as that patented seven months previously by Gray. The inventor further said that a number of these instruments might be placed on one circuit, and that if one of them were set in vibration, only those would respond which were in unison with its note; and further that “the duration of the sound may be used to indicate the dot or dash of the Morse alphabet, and thus a telegraphic despatch may be indicated by alternately interrupting and renewing the sound.”

Anything more totally different from Reis’s telephone than these selective harmonic telegraphs with their tuned tongues can hardly be imagined. Reis was not aiming at selective harmonic telegraphy; he wanted his one instrument to transmit every sound that a human ear could hear. He did not dream of using a tuned bar or reed; his typical structure was the tympanum of the ear. In fact, as we have seen above, the tuned reed or tongue was introduced into telegraphy for the purpose of transmitting single selected notes to the exclusion of all others.

Strange though it may seem, a tongue receiver like those of Graham Bell and of Gray just described can be used for receiving speech! It is true, as Gray remarks, that a thick bar of steel, cut away as described, is best adapted for its own tone only. But Bell’s thin steel tongue, though it has its own fundamental note (and so has every tympanum, for that matter) when left free to vibrate in its own time, will reproduce any other note or sound that may be forced upon it by the varying attraction of the electro-magnet. There is, indeed, the whole difference between “free” and “forced” vibrations. One of the strangest delusions that has somehow grown up in recent telephonic discussions is the almost incredible proposition that a tongue cannot talk because it is a tongue. It would be equally veracious to affirm that an ear (i.e. a tympanum) cannot hear because it is an ear.