But leaving harmonic telegraphy and its “tuned bars,” both Gray and Bell applied themselves to the old problem of transmitting human speech. What was their very first step? They threw away their “tuned bars” and “steel springs,” and returned to the tympanum! Elisha Gray devised the receiver shown in [Fig. 46], G, taken from his caveat of date February 14, 1876.[51] In that document Gray says: “My present belief is that the most effective method of providing an apparatus capable of responding to the various tones of the human voice, is a tympanum, drum, or diaphragm,” stretched across one end of a chamber. He adds that in the receiver there is (see [Fig. 46], G) an electro-magnet, acting upon a diaphragm to which is attached a piece of soft iron, and which diaphragm is stretched across a vocalising chamber.
Graham Bell’s receiver (the American specification of which was filed the same day as Gray’s caveat) is shown (in the form patented in Great Britain, Dec. 9, 1876) in [Fig. 46] H, which is taken from Fig. 19 of Bell’s British patent. “The armature,” says the inventor, “is fastened loosely by one extremity to the uncovered leg, h, of the electro-magnet E, and its other extremity is attached to the centre of a stretched membrane.” The armature, in fact, was capable of vibrating like a pendulum on its pivot, but was elastically restrained by its attachment to the tympanum; the armature would therefore vibrate in perfect correspondence with any vibrations forced upon it by the electro-magnet. This instrument as also that of Gray, was admirably adapted to receive speech, for it embodied the three essential points which Reis had already discovered: viz., firstly, that the armature must be of iron, or capable of being acted upon by magnetic induction; secondly, that it must be elastically mounted; thirdly, that it should present an extended surface. Bell’s form of receiver had the advantage over Reis’s (compare p. 158), that its extended surface was a true tympanum of membrane, and not a mere broad thin plank. Being a tympanum, it therefore realised Reis’s fundamental notion of imitating the human ear more fully than even Reis’s own receiver did.
Figures [46], J, K, and L represent the more recent types of receiver of Bell and Edison. [Fig. 46] J is reproduced from Fig. 20 of Bell’s British Patent, and shows the substitution of a thin steel plate, attached to a frame, in front of the electro-magnet, for the membrane and iron armature. This form of instrument also embodies Reis’s three principles—but with this improvement, the armature capable of inductive action, the elastic mounting, and the extended surface, are here all united in one organ, the thin flexible tympanum of steel. Apart from this unification of parts there is absolutely nothing in this form of Bell’s receiver, that Reis did not invent fourteen years before. Bell’s great and most signal improvement was not this beautiful mechanical modification of the Reis receiver, but lay in the entirely new suggestion to use such a receiver as a transmitter to work by magneto-electric induction. Two of Reis’s receivers ([Fig. 21]) if coupled up with a battery will talk together as transmitter and receiver: but Reis did not know and never suggested this. Two of Yeates’s receivers ([Fig. 42]) if coupled up with a battery will talk together as transmitter and receiver; but Yeates did not know and never suggested this. Bell did discover this, and thereby invented a transmitter which, though now abandoned as a transmitter, for want of loudness, was more reliable than the anterior transmitters of Reis had been. He made another discovery, presently to be alluded to—that of putting a permanent magnet into the transmitter, to enable him to dispense with the battery; but beyond this and the other mechanical simplifications previously mentioned, all that he discovered may be summed up by saying that he found out that a receiver constructed on Reis’s principles could work as a transmitter also. That was Bell’s really great and important discovery which took all the world by storm at the Centennial Exhibition of 1876.
Bell subsequently added to his claims the substitution of a permanent magnet with an iron pole-piece, in place of the simple electro-magnet, thus enabling him to transmit his fluctuating currents without the trouble of using a battery, and the Bell transmitter, thus modified, is used to this day as a receiver, Reis had in his “knitting-needle” telephone, employed a permanent magnet of steel to serve as a receiver, he had not, however, applied it as Bell did to attract a plate of thin steel.
[Fig. 46], K, exhibits a form of electro-magnetic receiver described in Edison’s British Specification, No. 2909, 1877, Fig. 24. This instrument, though patented seven months after Bell’s instrument, differs from it in no point of importance. Its armature was a thin plate of iron, elastic, and having an extended surface; being, in fact, a tympanum.
No one can examine the set of receiving instruments collected in [Fig. 46] without being struck with the extraordinary similarity of design which pervades the entire series. In every one of the set there is an electro-magnet, the function of which is to set an armature[52] into vibration by attracting it with a variable force. In every one the armature is of a material capable of magnetic induction; that is to say, iron, steel, or equivalent material. In every one of them the armature is either elastically mounted, or is in itself elastic. In every one of them (save only the two quite recent forms, F and I, which were intended not to speak, but to emit only one fixed musical note) there is an extended surface (either a sound-board or a tympanum) to communicate the vibrations to the air. Lastly, every one of these forms, when connected with the line through which the telephonic currents are being transmitted, is perfectly capable of reproducing articulate speech. But the inventor who had the genius to discover all these essential points, and to combine them in an instrument, and to use it to reproduce articulate speech, is surely the true inventor of the system. The inventor of the system embodying these essential points was Philipp Reis.
APPENDIX IV.
On the Doctrine of Undulatory Currents.
“In this Specification the three words ‘oscillation,’ ‘vibration’ and ‘undulation,’ are used synonymously.”—Graham Bell, U.S. Patent, No. 174,465, filed Feb. 14, 1876.