THE INVENTION OF THE TELEPHONE-THE SHARE IN IT OF BELL AND EDISON

(1877)

THE "ENCYCLOPEDIA BRITANNICA'S"

ACCOUNT1

In 1831 Wheatstone, by his "magic lyre" experiment, showed that, when the sounding-boards of two musical instruments are connected together by a rod of pine wood, a tune played on one will be faithfully reproduced by the other. This only answers, however, for telephoning musical sounds to short distances. Another and somewhat similar example is furnished by what has been variously designated as the "string," "toy," "lovers'," and "mechanical" telephone. Two disks of thin metal, or two stretched membranes, each furnished with a mouthpiece, are connected together by a thin string or wire attached at each end to the centers of the membranes. A good example may be made with two cylindrical tin cups; the bottoms form the membranes and the cups the mouthpieces.

In July, 1837, Dr. C. G. Page, of Salem, Massachusetts, drew attention to the sound given out by an electromagnet at the instant when the electric circuit is closed or broken, and in October of the same year he discust, in a short article entitled "Galvanic Music," the musical

1 From an article in the ninth edition of the "Britannica."

note produced by rapidly revolving the armature of an electromagnet in front of the poles. Experiments bearing on this subject were subsequently made by a great number of investigators. Page's discovery is of considerable importance in connection with the theory of action of various forms of telephone, and was a very important feature in the early attempts by Reis to transmit music and speech.

On August 26, 1854, there appeared in L'Illustration (Paris) an interesting article by Charles Bourseul on the electric transmission of speech. The writer recommended the use of a flexible plate at the source of sound, which would vibrate in response to the varying pressure of the air, and thus open and close an electric circuit, and of a similar plate at the receiving station, which would be acted on electromagnetically and thus give out as many pulsations as there are breaks in the current. These suggestions were to some extent an anticipation of the work of Reis; but the conditions to be fulfilled before the sounds given out at the receiving station can be similar in pitch, quality, and relative intensity to those produced at the transmitting station are not stated, and do not seem to have been appreciated.

In Reis's lecture an apparatus was described which has given rise to much discussion as to priority in the invention of the telephone. The instrument was described in over fifty publications in various countries, and was well known to physicists previous to Bell's introduction of the electric telephone as a competitor with the electric telegraph. Reis caused a membrane to

open and close an electric circuit at each vibration, thus transmitting as many electric pulses through the circuit as there were vibrations in the sound. These electric pulses were made to act on an electromagnet at the receiving station, which, in accordance with Page's discovery, gave out a sound of a pitch corresponding to the number of times it was magnetized or demagnetized per second.

The next worker at the telephone, and the one to whom the present great commercial importance of the instrument is due, was Bell.' His aim was the production, by means of the undulations of pressure on a membrane caused by sound, of an electric current the strength of which should at every instant vary directly as the pressure varied. His first idea seems to have been to employ the vibrations of the current in an electric circuit, produced by moving the armature of an electromagnet included in the circuit nearer to or farther from the poles of the magnet. He proposed to make the armature partake of the vibrations of the atmosphere either by converting it into a suitable vibrator or by controlling its vibrations by a stretched membrane of parchment. In the early trials the armature had the form of a hinged lever of iron carrying a stud at one end, which prest against the center of a stretched membrane.

The experiments with this form were not suc

Alexander Graham Bell was born in Edinburgh in 1847, and came to America in 1870. He settled in Boston the next year as a professor of vocal physiology. Six years later his invention of the telephone was announced. His home is

now in Washington.

cessful, and, with the view of making the moving parts as light as possible, he substituted for the comparatively heavy lever armature a small piece of clock-spring, about the size of a sixpence, glued to the center of the diaphragm. The magnet was mounted with its end carrying the coil opposite, and very close to, the center of the piece of clock-spring. This answered sufficiently well to prove the feasibility of the plan, and subsequent experiments were directed to the discovery of the best form and arrangement of the parts. An increase in the size of the iron disk attached to the membrane augmented both the loudness and the distinctness of the sounds, and this finally led to the adoption of the thin iron disk now in use, which is supported around its edge, and acts as both membrane and armature. Again, the form of the opening or mouthpiece in front of the membrane exercised considerable influence on the efficiency of the instrument, and it was ultimately ascertained that a small central opening, with a thin air space extending across the face of the membrane, was best.

It was also found that comparatively small magnets were sufficient, and that there was no particular virtue in the closed circuit and electromagnet, but that a small permanent magnet having one pole in contact with the end of the core of a short electromagnet, the coil of which was in circuit with the line, but which had no permanent current flowing through it, answered the purpose quite as well. In fact, the effect of keeping a permanent current flowing through the line, and the coils of the electromagnet was to