CHAPTER VIII. THE TELEPHONE TRANSMITTER AND RECEIVER. THE PHOTO PHONE. THE THERMOPHONE. THE SELENIUM CELL. THE SPEAKING ARC.The telephone is an instrument for the transmission of sounds to a distance by the agency of electricity, wherein the speaker talks to an elastic plate of thin sheet-iron, which vibrates and transmits its every movement, electrically, causing it to vibrate in an identical manner and emit the same sounds.The transmission of the vibrations depends upon well known principles of electricity, and consists, not of an actual transmission of the sounds, but the passage of electric waves, or impulses, which keep perfect accord and agree in phase and period with the atmospheric waves produced by the voice. These in turn, through the medium of an electromagnet, cause vibrations of a plate or membrane, which agitates the air in a manner similar to the original disturbance, and thus emits sounds.The parts of the apparatus which take up the sound waves and change them into electric currents compose thetransmitter. In the form of transmitter most commonly used, the motions of the diaphragm cause variations in the strength of a current flowing from a battery by varying the resistance in the path of the electric current.The sounds are directed to the mouthpiece, which causes the vibrations of the air to strike the diaphragm, on the back and center of which is fastened a small cup shaped piece of carbon. A second cup is mounted in a rigid position directly in back of the first. The space between is filled with small polished granules of carbon,FIG. 131.—Diagram of a telephone transmitter.FIG. 131.—Diagram of a telephone transmitter.When these are in a perfectly free and loose state their resistance to an electric current is very great, and they allow almost none to flow.When slightly compressed their resistance is greatly lowered, and they permit the current to pass. The vibrations of the diaphragm exert a varying pressure upon the granules, with a corresponding variation in their resistance and the amount of current flowing.FIG. 132.—Diagram showing the principle and construction of the telephone receiver.FIG. 132.—Diagram showing the principle and construction of the telephone receiver.The receiver, as has already been explained, consists of a thin iron disk, placed very near but not quite touching the end of a small bar of steel, permanently magnetized, about which is wound a coil of fine insulated wire. The ends of this coil are connected to the wires leading from the transmitter and battery. The varying currents of electricity, produced by the transmitter, generate corresponding changes in the magnetism of the receiving instrument, and thus, by alternately attracting and repelling the diaphragm, cause it to vibrate and emit sounds.FIG. 133.—The photophone.FIG. 133.—The photophone.Alexander Graham Bell, the ingenious inventor of the telephone, with the aid of Sumner Tainter was the first who achieved success in the attempts to transmit speech without the aid of connecting wires between the source of intelligence and the receptor.In 1873 Willoughby Smith announced that the elementseleniumpossesses the abnormal property of changing its electrical resistance under the influence of light. Bell and Tainter took advantage of this discovery, and devisedselenium cells, in which selenium is formed into narrow strips between the edges of broad conducting plates of brass. The resistance of the cell in the darkness is approximately twice the resistance when illuminated.FIG. 134.—Photophone receiving apparatus.FIG. 134.—Photophone receiving apparatus.FIG. 135.—Photophone transmitting apparatus, using acetylene flame to furnish light.FIG. 135.—Photophone transmitting apparatus, using acetylene flame to furnish light.This property of the cell was immediately applied to the construction of thephotophone, an instrument which transmits sounds to a distance by means of a beam of light reflected to a distant spot from a thin mirror thrown into vibration by the voice. Over fifty different forms were devised but the most successful consisted of a transmitter composed of a glass disk, silvered to reflect a pencil of light focused from the sun, or an arc lamp. This glass disk was used as a diaphragm similar to that of an ordinary telephone transmitter, except that the rear side of it was made free to reflect the beam of light. Bell used for this purpose disks about two inches in diameter and the thickness of ordinary paper. The receiver consisted of a parabolic reflector, with a selenium cell placed at its focus. In series with the cell was placed a battery and telephone receiver.When the membrane was set into vibration by the sound waves, it became alternately concave and convex, the normally parallel rays of light correspondingly converging and diverging. The receiving station was thus under the influence of light rays of rapidly varying intensity in perfect phase with the vibrations of the voice. The reflector concentrated the rays on the selenium cell, and their varying strength changed its resistance and caused a pulsating current to flow through the receiver and reproduce the speech produced at the transmitter.In another arrangement employed by Bell and Tainter, they used the rays of a powerful electric arc lamp, and by varying the electric current supplying the arc caused the light to fluctuate and produce the same results at the receiver.These ingenious inventors also devised a method of transmitting speech called thethermophone. The transmitter remained the same as in the photophone–a thin silvered membrane, or glass diaphragm, stretched across the back of a mouthpiece, and arranged to reflect the rays of the sun, or the light of an arc lamp.The receiver was a small glass bulb containing a plate of mica covered with lampblack, or little charred pieces of cork. The glass bulb was placed in the focus of a reflector, which collected the rays and concentrated them. The variations in the intensity of the heat radiations caused the air in the bulb to expand or contract with each vibration. Rubber tubes extended from the bulb to the ears of the observer, and the pulsations of air, traveling through the tube as sound waves, would strike the ear-drum and reproduce the speech.FIG. 136.—Powerful searchlight arranged to transmit speech over a beam of light.FIG. 136.—Powerful searchlight arranged to transmit speech over a beam of light.Both of these methods were later very much improved by the employment of Koenig's manometric flame in place of the silvered mirror as a transmitter. As explained in the last chapter, speech delivered into the mouthpiece causes the gas to become compressed or rarefied in direct accordance with the sound waves, and the flame rises and falls with a rapidity too great to be detected by the naked eye. These rapid alterations in the intensity of the illumination of the flame act on the selenium cell, and reproduce the original voice perfectly in the telephone receiver.FIG. 137.—The Electric arc.FIG. 137.—The Electric arc.It is obvious, however, that such methods as these are only capable of transmitting speech over very limited distances, and if greater ranges are to be traversed much more powerful transmitters must be employed for the purpose.Ernest Ruhmer, after long and laborious researches, finally succeeded in transmitting speech many miles by taking advantage of thespeaking arc, discovered by Simon, who observed that an arc lamp gave out a loud rattling noise if its current supply was interfered with. An electric arc consists of two carbon rods, connected to a generator. When the carbons are brought into contact for a moment and then drawn apart to a short distance, a kind of electric flame orarcis produced between the points of carbon, and a brilliant white light is emitted by the white hot points of the carbon electrodes.Ruhmer immediately made the arc serve as a telephone receiver andspeakby utilizing the pulsating current of a telephone transmitter to vary the current supplying the arc.FIG. 138.—Circuit showing how a singing arc is arranged.FIG. 138.—Circuit showing how a singing arc is arranged.The arc could thus be made to sing, whistle or reproduce music and the human voice perfectly, if the sounds were clearly conveyed into the transmitter. Further investigations showed that every alteration of current caused by the action of the transmitter also caused an alteration in the intensity of the light and radiation of the lamp. The speaking arc could therefore be used as a perfect photophone transmitter by directing the rays toward the receiving station with the aid of a parabolic reflector.In 1902 Ruhmer performed a series of experiments in Germany on the Wannsee, near Berlin. A large motorboat, theGermania, was fitted with an electric searchlight connected with a microphone, so as to form a speaking arc. The receiving station was located on the shore, so that the distance between the stations could be easily enlarged by moving the boat.The receptor was an ordinary selenium cell, placed at the focus of a large reflector and connected with a telephone receiver and battery. No difficulty was encountered in reproducing the speech over varying distances up to about three miles.
CHAPTER VIII. THE TELEPHONE TRANSMITTER AND RECEIVER. THE PHOTO PHONE. THE THERMOPHONE. THE SELENIUM CELL. THE SPEAKING ARC.The telephone is an instrument for the transmission of sounds to a distance by the agency of electricity, wherein the speaker talks to an elastic plate of thin sheet-iron, which vibrates and transmits its every movement, electrically, causing it to vibrate in an identical manner and emit the same sounds.The transmission of the vibrations depends upon well known principles of electricity, and consists, not of an actual transmission of the sounds, but the passage of electric waves, or impulses, which keep perfect accord and agree in phase and period with the atmospheric waves produced by the voice. These in turn, through the medium of an electromagnet, cause vibrations of a plate or membrane, which agitates the air in a manner similar to the original disturbance, and thus emits sounds.The parts of the apparatus which take up the sound waves and change them into electric currents compose thetransmitter. In the form of transmitter most commonly used, the motions of the diaphragm cause variations in the strength of a current flowing from a battery by varying the resistance in the path of the electric current.The sounds are directed to the mouthpiece, which causes the vibrations of the air to strike the diaphragm, on the back and center of which is fastened a small cup shaped piece of carbon. A second cup is mounted in a rigid position directly in back of the first. The space between is filled with small polished granules of carbon,FIG. 131.—Diagram of a telephone transmitter.FIG. 131.—Diagram of a telephone transmitter.When these are in a perfectly free and loose state their resistance to an electric current is very great, and they allow almost none to flow.When slightly compressed their resistance is greatly lowered, and they permit the current to pass. The vibrations of the diaphragm exert a varying pressure upon the granules, with a corresponding variation in their resistance and the amount of current flowing.FIG. 132.—Diagram showing the principle and construction of the telephone receiver.FIG. 132.—Diagram showing the principle and construction of the telephone receiver.The receiver, as has already been explained, consists of a thin iron disk, placed very near but not quite touching the end of a small bar of steel, permanently magnetized, about which is wound a coil of fine insulated wire. The ends of this coil are connected to the wires leading from the transmitter and battery. The varying currents of electricity, produced by the transmitter, generate corresponding changes in the magnetism of the receiving instrument, and thus, by alternately attracting and repelling the diaphragm, cause it to vibrate and emit sounds.FIG. 133.—The photophone.FIG. 133.—The photophone.Alexander Graham Bell, the ingenious inventor of the telephone, with the aid of Sumner Tainter was the first who achieved success in the attempts to transmit speech without the aid of connecting wires between the source of intelligence and the receptor.In 1873 Willoughby Smith announced that the elementseleniumpossesses the abnormal property of changing its electrical resistance under the influence of light. Bell and Tainter took advantage of this discovery, and devisedselenium cells, in which selenium is formed into narrow strips between the edges of broad conducting plates of brass. The resistance of the cell in the darkness is approximately twice the resistance when illuminated.FIG. 134.—Photophone receiving apparatus.FIG. 134.—Photophone receiving apparatus.FIG. 135.—Photophone transmitting apparatus, using acetylene flame to furnish light.FIG. 135.—Photophone transmitting apparatus, using acetylene flame to furnish light.This property of the cell was immediately applied to the construction of thephotophone, an instrument which transmits sounds to a distance by means of a beam of light reflected to a distant spot from a thin mirror thrown into vibration by the voice. Over fifty different forms were devised but the most successful consisted of a transmitter composed of a glass disk, silvered to reflect a pencil of light focused from the sun, or an arc lamp. This glass disk was used as a diaphragm similar to that of an ordinary telephone transmitter, except that the rear side of it was made free to reflect the beam of light. Bell used for this purpose disks about two inches in diameter and the thickness of ordinary paper. The receiver consisted of a parabolic reflector, with a selenium cell placed at its focus. In series with the cell was placed a battery and telephone receiver.When the membrane was set into vibration by the sound waves, it became alternately concave and convex, the normally parallel rays of light correspondingly converging and diverging. The receiving station was thus under the influence of light rays of rapidly varying intensity in perfect phase with the vibrations of the voice. The reflector concentrated the rays on the selenium cell, and their varying strength changed its resistance and caused a pulsating current to flow through the receiver and reproduce the speech produced at the transmitter.In another arrangement employed by Bell and Tainter, they used the rays of a powerful electric arc lamp, and by varying the electric current supplying the arc caused the light to fluctuate and produce the same results at the receiver.These ingenious inventors also devised a method of transmitting speech called thethermophone. The transmitter remained the same as in the photophone–a thin silvered membrane, or glass diaphragm, stretched across the back of a mouthpiece, and arranged to reflect the rays of the sun, or the light of an arc lamp.The receiver was a small glass bulb containing a plate of mica covered with lampblack, or little charred pieces of cork. The glass bulb was placed in the focus of a reflector, which collected the rays and concentrated them. The variations in the intensity of the heat radiations caused the air in the bulb to expand or contract with each vibration. Rubber tubes extended from the bulb to the ears of the observer, and the pulsations of air, traveling through the tube as sound waves, would strike the ear-drum and reproduce the speech.FIG. 136.—Powerful searchlight arranged to transmit speech over a beam of light.FIG. 136.—Powerful searchlight arranged to transmit speech over a beam of light.Both of these methods were later very much improved by the employment of Koenig's manometric flame in place of the silvered mirror as a transmitter. As explained in the last chapter, speech delivered into the mouthpiece causes the gas to become compressed or rarefied in direct accordance with the sound waves, and the flame rises and falls with a rapidity too great to be detected by the naked eye. These rapid alterations in the intensity of the illumination of the flame act on the selenium cell, and reproduce the original voice perfectly in the telephone receiver.FIG. 137.—The Electric arc.FIG. 137.—The Electric arc.It is obvious, however, that such methods as these are only capable of transmitting speech over very limited distances, and if greater ranges are to be traversed much more powerful transmitters must be employed for the purpose.Ernest Ruhmer, after long and laborious researches, finally succeeded in transmitting speech many miles by taking advantage of thespeaking arc, discovered by Simon, who observed that an arc lamp gave out a loud rattling noise if its current supply was interfered with. An electric arc consists of two carbon rods, connected to a generator. When the carbons are brought into contact for a moment and then drawn apart to a short distance, a kind of electric flame orarcis produced between the points of carbon, and a brilliant white light is emitted by the white hot points of the carbon electrodes.Ruhmer immediately made the arc serve as a telephone receiver andspeakby utilizing the pulsating current of a telephone transmitter to vary the current supplying the arc.FIG. 138.—Circuit showing how a singing arc is arranged.FIG. 138.—Circuit showing how a singing arc is arranged.The arc could thus be made to sing, whistle or reproduce music and the human voice perfectly, if the sounds were clearly conveyed into the transmitter. Further investigations showed that every alteration of current caused by the action of the transmitter also caused an alteration in the intensity of the light and radiation of the lamp. The speaking arc could therefore be used as a perfect photophone transmitter by directing the rays toward the receiving station with the aid of a parabolic reflector.In 1902 Ruhmer performed a series of experiments in Germany on the Wannsee, near Berlin. A large motorboat, theGermania, was fitted with an electric searchlight connected with a microphone, so as to form a speaking arc. The receiving station was located on the shore, so that the distance between the stations could be easily enlarged by moving the boat.The receptor was an ordinary selenium cell, placed at the focus of a large reflector and connected with a telephone receiver and battery. No difficulty was encountered in reproducing the speech over varying distances up to about three miles.
The telephone is an instrument for the transmission of sounds to a distance by the agency of electricity, wherein the speaker talks to an elastic plate of thin sheet-iron, which vibrates and transmits its every movement, electrically, causing it to vibrate in an identical manner and emit the same sounds.
The transmission of the vibrations depends upon well known principles of electricity, and consists, not of an actual transmission of the sounds, but the passage of electric waves, or impulses, which keep perfect accord and agree in phase and period with the atmospheric waves produced by the voice. These in turn, through the medium of an electromagnet, cause vibrations of a plate or membrane, which agitates the air in a manner similar to the original disturbance, and thus emits sounds.
The parts of the apparatus which take up the sound waves and change them into electric currents compose thetransmitter. In the form of transmitter most commonly used, the motions of the diaphragm cause variations in the strength of a current flowing from a battery by varying the resistance in the path of the electric current.
The sounds are directed to the mouthpiece, which causes the vibrations of the air to strike the diaphragm, on the back and center of which is fastened a small cup shaped piece of carbon. A second cup is mounted in a rigid position directly in back of the first. The space between is filled with small polished granules of carbon,
FIG. 131.—Diagram of a telephone transmitter.FIG. 131.—Diagram of a telephone transmitter.
FIG. 131.—Diagram of a telephone transmitter.
When these are in a perfectly free and loose state their resistance to an electric current is very great, and they allow almost none to flow.
When slightly compressed their resistance is greatly lowered, and they permit the current to pass. The vibrations of the diaphragm exert a varying pressure upon the granules, with a corresponding variation in their resistance and the amount of current flowing.
FIG. 132.—Diagram showing the principle and construction of the telephone receiver.FIG. 132.—Diagram showing the principle and construction of the telephone receiver.
FIG. 132.—Diagram showing the principle and construction of the telephone receiver.
The receiver, as has already been explained, consists of a thin iron disk, placed very near but not quite touching the end of a small bar of steel, permanently magnetized, about which is wound a coil of fine insulated wire. The ends of this coil are connected to the wires leading from the transmitter and battery. The varying currents of electricity, produced by the transmitter, generate corresponding changes in the magnetism of the receiving instrument, and thus, by alternately attracting and repelling the diaphragm, cause it to vibrate and emit sounds.
FIG. 133.—The photophone.FIG. 133.—The photophone.
FIG. 133.—The photophone.
Alexander Graham Bell, the ingenious inventor of the telephone, with the aid of Sumner Tainter was the first who achieved success in the attempts to transmit speech without the aid of connecting wires between the source of intelligence and the receptor.
In 1873 Willoughby Smith announced that the elementseleniumpossesses the abnormal property of changing its electrical resistance under the influence of light. Bell and Tainter took advantage of this discovery, and devisedselenium cells, in which selenium is formed into narrow strips between the edges of broad conducting plates of brass. The resistance of the cell in the darkness is approximately twice the resistance when illuminated.
FIG. 134.—Photophone receiving apparatus.FIG. 134.—Photophone receiving apparatus.
FIG. 134.—Photophone receiving apparatus.
FIG. 135.—Photophone transmitting apparatus, using acetylene flame to furnish light.FIG. 135.—Photophone transmitting apparatus, using acetylene flame to furnish light.
FIG. 135.—Photophone transmitting apparatus, using acetylene flame to furnish light.
This property of the cell was immediately applied to the construction of thephotophone, an instrument which transmits sounds to a distance by means of a beam of light reflected to a distant spot from a thin mirror thrown into vibration by the voice. Over fifty different forms were devised but the most successful consisted of a transmitter composed of a glass disk, silvered to reflect a pencil of light focused from the sun, or an arc lamp. This glass disk was used as a diaphragm similar to that of an ordinary telephone transmitter, except that the rear side of it was made free to reflect the beam of light. Bell used for this purpose disks about two inches in diameter and the thickness of ordinary paper. The receiver consisted of a parabolic reflector, with a selenium cell placed at its focus. In series with the cell was placed a battery and telephone receiver.
When the membrane was set into vibration by the sound waves, it became alternately concave and convex, the normally parallel rays of light correspondingly converging and diverging. The receiving station was thus under the influence of light rays of rapidly varying intensity in perfect phase with the vibrations of the voice. The reflector concentrated the rays on the selenium cell, and their varying strength changed its resistance and caused a pulsating current to flow through the receiver and reproduce the speech produced at the transmitter.
In another arrangement employed by Bell and Tainter, they used the rays of a powerful electric arc lamp, and by varying the electric current supplying the arc caused the light to fluctuate and produce the same results at the receiver.
These ingenious inventors also devised a method of transmitting speech called thethermophone. The transmitter remained the same as in the photophone–a thin silvered membrane, or glass diaphragm, stretched across the back of a mouthpiece, and arranged to reflect the rays of the sun, or the light of an arc lamp.
The receiver was a small glass bulb containing a plate of mica covered with lampblack, or little charred pieces of cork. The glass bulb was placed in the focus of a reflector, which collected the rays and concentrated them. The variations in the intensity of the heat radiations caused the air in the bulb to expand or contract with each vibration. Rubber tubes extended from the bulb to the ears of the observer, and the pulsations of air, traveling through the tube as sound waves, would strike the ear-drum and reproduce the speech.
FIG. 136.—Powerful searchlight arranged to transmit speech over a beam of light.FIG. 136.—Powerful searchlight arranged to transmit speech over a beam of light.
FIG. 136.—Powerful searchlight arranged to transmit speech over a beam of light.
Both of these methods were later very much improved by the employment of Koenig's manometric flame in place of the silvered mirror as a transmitter. As explained in the last chapter, speech delivered into the mouthpiece causes the gas to become compressed or rarefied in direct accordance with the sound waves, and the flame rises and falls with a rapidity too great to be detected by the naked eye. These rapid alterations in the intensity of the illumination of the flame act on the selenium cell, and reproduce the original voice perfectly in the telephone receiver.
FIG. 137.—The Electric arc.FIG. 137.—The Electric arc.
FIG. 137.—The Electric arc.
It is obvious, however, that such methods as these are only capable of transmitting speech over very limited distances, and if greater ranges are to be traversed much more powerful transmitters must be employed for the purpose.
Ernest Ruhmer, after long and laborious researches, finally succeeded in transmitting speech many miles by taking advantage of thespeaking arc, discovered by Simon, who observed that an arc lamp gave out a loud rattling noise if its current supply was interfered with. An electric arc consists of two carbon rods, connected to a generator. When the carbons are brought into contact for a moment and then drawn apart to a short distance, a kind of electric flame orarcis produced between the points of carbon, and a brilliant white light is emitted by the white hot points of the carbon electrodes.
Ruhmer immediately made the arc serve as a telephone receiver andspeakby utilizing the pulsating current of a telephone transmitter to vary the current supplying the arc.
FIG. 138.—Circuit showing how a singing arc is arranged.FIG. 138.—Circuit showing how a singing arc is arranged.
FIG. 138.—Circuit showing how a singing arc is arranged.
The arc could thus be made to sing, whistle or reproduce music and the human voice perfectly, if the sounds were clearly conveyed into the transmitter. Further investigations showed that every alteration of current caused by the action of the transmitter also caused an alteration in the intensity of the light and radiation of the lamp. The speaking arc could therefore be used as a perfect photophone transmitter by directing the rays toward the receiving station with the aid of a parabolic reflector.
In 1902 Ruhmer performed a series of experiments in Germany on the Wannsee, near Berlin. A large motorboat, theGermania, was fitted with an electric searchlight connected with a microphone, so as to form a speaking arc. The receiving station was located on the shore, so that the distance between the stations could be easily enlarged by moving the boat.
The receptor was an ordinary selenium cell, placed at the focus of a large reflector and connected with a telephone receiver and battery. No difficulty was encountered in reproducing the speech over varying distances up to about three miles.