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One of the most remarkable recent inventions connected with telegraphy is the telephone, an instrument which transmits directly the pitch of a sound by means of a telegraphic wire - either an air-wire or submarine cable; so that, for instance, when the operator at one end of the wire sings or plays on an instrument any time, as Yankee Doodle or Hail Columbia, it will be heard and distinguished plainly at the other end. This invention may, in its present state, have no direct practical application, but be a mere scientific, although highly interesting curiosity; but who can say that it does not contain the germ of a new method of working the telegraph, or some other useful practical purpose.

The telephone is not the result of an accidental discovery, but of a thorough study of the laws of electromagnetism and of sound. It is founded on the fact that the difference in pitch of different tones is caused by different velocities of vibrations of the elastic sounding body; which vibrations are transmitted to and by the air with exactly the same velocity, and from the air may be communicated to a properly stretched membrane, like a piece of bladder or very thin sheet of India-rubber, stretched like a drum-head, which these also will vibrate with exactly the same velocity as the air and the original sounding body, be it the human voice, organ-pipe, string or any musical instrument. If, now, at the centre of this little drum-head there be attached a small disk of some metal not easily burned by electric currents - for instance platinum - while at the same time a platinum point may, by means of a screw, be so adjusted as to come very nearly in contact with this small platinum disk, it is clear that, when the membrane is put in vibration, a succession of contacts between the disk and point will be produced, of which the number in each second will exactly correspond with the number of vibrations in each second of the sounding body, or the tone produced by it.

That part of the apparatus which serves to send off the tone or melody is represented in illustration figure 1. It consists simply of a square wooden box, provided at the side with a kind of mouth-piece similar to that of a speaking tube, and at the top with an opening, over which the membrane just mentioned has been stretched. The small disk of platinum attached to the centre of this little drum-head is, by means of a very flexible strip of some metal that conducts well, attached to one pole of the galvanic battery, of which only cup is represented in the figure, although for a long wire several cups will, of course, be required. The reason why this connection near the platinum disk is a flat, thin and flexible strip is that any rigidity would interfere with the freedom of vibration of the membrane to which it is attached. The point coming in contact with this small vibrating disk is connected with the ground wire, the other pole of the battery with the air wire or submarine cable.

It is clear, from this explanation, that at every contact of the platinum point a wave of electricity will be sent over the wire, and as many waves in a second as there are contacts; and as there as many contacts as there are vibrations in every second, the number of electric waves will be always exactly equal to the number of vibrations corresponding with the pitch of each tone, be it fifty, one hundred, two hundred, or five hundred in every second.

The instrument in which this succession of waves is made audible at the other end of the telegraph wire is founded on the fact, first investigated by Professor Henry of the Smithsonian Institute at Washington, that iron bars, when becoming magnetic by means of electric currents passing around them, become slightly elongated, and at the interruption of the current are at once restored to their original length. It is represented in the cut, figure 2, and consists of an elongated wooden box, of which the top is made of thin pine wood, similar to the sounding board of a stringed musical instrument, to which are attached two bridges carrying long pieces of moderately thick and very soft iron wire, which for nearly their whole length are surrounded by a coil similar to the coil of the electro magnets used in telegraphing. One end of this coil is attached to the telegraph wire, the other to the ground wire as represented in the figure. At every instant that a contact is established at the station where the sound is produced, and a current wave thus transmitted, these wires will become magnetic, and consequently elongated, and they will be shortened again at every interruption of the current; and as these currents and interruptions succeed each other with the same velocity as the sound vibrations, the elongations and shortenings of the magnetised iron wires will succeed each other with exactly the same velocity, and consequently they will be thrown into a state of longitudinal vibrations corresponding with the original musical tone, which vibrations will then be communicated to the sounding board in exactly the same manner as is the case with the vibrations of the strings in all stringed instruments, thus becoming more audible at the receiving station.

It is clear from the foregoing explanations, that no quality of tone can be transmitted. Much less can articulate words be sent, not withstanding the enthusiastic prediction of some persons, who, when they first beheld the apparatus in operation, exclaimed that now we could talk directly through the wire. It is from its nature able to transmit only pitch and rhythm, consequently melody, and nothing more. No harmony, nor different degrees of strength or other qualities of tone can be transmitted; the receiving instrument in fact sings the melodies transmitted as it were with its own voice, resembling the humming of an insect, regardless of the quality of the tone which produces the original tone at the other end of the wire. This instrument is a German invention, and was first exhibited, in New York, at the Polytechnic Association of the American Institute, by Dr. Van der Weyde. The original sounds were produced at the further extremity of the large building, (the Cooper Institute) totally out of hearing of the association; and the receiving instrument, standing on a table of the lecturer, produced with its own rather nasal twang the different tunes sung at the other end of the line, rather weakly, it is true, because of the weak battery used, but very distinctly and correctly

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