Scientific American Supplement No. 58 page 912 2/10/1877
THE articulating telephone of Mr. Graham Bell, like those of Reis and Gray, consists of two parts, a transmitting instrument and a receiver, and one cannot but be struck at the extreme simplicity of both instruments, so simple indeed that were it not for the high authority of Sir William Thomson one might be pardoned at entertaining some doubts of their capability of producing such marvellous results.
The transmitting instrument, which is represented in fig.1 consists of a horizontal electro-magnet attached to a pillar about 3 inches above a horizontal mahogany stand • inbraue can be tightened like a drum by the three mill-headed screws shown in the drawing. The ends of the coil surrounding the magnet terminate in two binding screws by which the instrument is put in circuit with the receiving instrument, which is shown in Fig. 2. This instrument is nothing more than one of the tubular electro-magnets invented by M. Niclses in the year 1853, but which has been reinvented under various fancy names several times since. It consists of a vertical bar electro-magnet enclosed in a tube of soft iron, by which its magnetic field is condensed and its attractive power within that area increased. Over this is fixed, attached by a screw at a point near its circumference, a thin sheet iron armature of the thickness of a sheet of cartridge paper, and this when under the influence of the transmitted currents acts partly as a vibrator and partly as a resonator. The magnet with its armature is mounted upon a little bridge which is attached to a mahogany stand. similar to that of the transmitting instrument.
The action of the apparatus is as follows: When a note or a word is sounded into the mouthpiece of the transmitter, its membrane vibrates in unison with the sound, and in doing BO carries the soft iron inductor attached to it backwards and forwards in presence of the electro-magnet, inducing a series of magneto-electric currents in its surrounding helix, which are transmitted by the conducting wire to the receiving instrument, and a corresponding vibration is therefore set up in the thin iron armature sufficient to produce sonorous vibrations by which articulated words can be distinctly and clearly recognized.
In all previous attempts at producing this result, the vibrations were produced by a make-and-break arrangement, so that while the number of vibrations per second as well as the time measures were correctly transmitted, there was no variation in the strength of the current, whereby the quality of tone was also recorded. This defect did not prevent the transmission of pure musical notes, nor even the discord produced by a mixture of them, but the complicated variations of tone, of quality, and of modulation which make up the human voice, required something more than a mere isochronism of vibratory impulses.
n Mr. Bell's apparatus not only are the vibrations in the receiving instrument isochronous with those of the transmitting membrane, but they are at the same time similar in quality to the sound producing them, for the currents being induced by an inductor vibrating with the voice, differences of amplitude of vibrations cause differences in strength of the impulses, and the articulate sound as of a person speaking is produced at the other end.
Of the capabilities of this very beautiful invention we cannot give them better than in the words of an ear-witness, and no less an authority than Sir William Thomson, who, in his opening address to Section A at the British Association at Glasgow, thus referred to it:
In the Canadian Department I heard 'To be or not to be........there's
the rub,' through an electric telegraph wire- but scorning monosyllables,
the electric articulation rose to higher flights, and gave me passages taken
at random from the New York newspapers: • S. S. Cox has arrived (I failed to
make out the 'S. S. Cox'); • the City of New York;' ' Senator Morton; -the
Senate has resolved to print a thousand extra copies;' "the Americans in
London have resolved to celebrate the coming 4th of July.' All this my own
ears heard spoken to me with unmistakable distinctness by the then circular
disk armature of just such another little electro-magnet as this which I
hold in my hand. The words were shouted with a clear and loud voice by my
colleague•judge Professor Watson, at the far end of the telegraph wire
holding his mouth close to a stretched membrane, such as you see before you
here, carrying a little piece of soft iron, which was thus made to perform
in the neighborhood of an electro-magnet, in circuit with the line, motions
proportional to the sonoriflc motions of the air. This, the greatest by far
of all the marvels of the electric telegraph, is due to Mr. Graham Bell, of
Edinburgh, and Montreal, and Boston, now becoming a naturalized citizen of
the United States. "Who can but admire the hardihood of invention which
devised such very slight means to realize the mathematical conception that,
if electricity is to convey all the delicacies of quality which distinguish
articulate speech, the strength of its current must vary continuously and as
nearly as may be in simple proportion to the velocity of a particle. of air
engaged in constituting the sound."- Engineering,
