Latest / History of the Universe Physics & Electricity Vol. 3 / 027 - Electricity - Chapter 8 - The Telephone Part 2

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027 - Electricity - Chapter 8 - The Telephone Part 2 · History of the Universe Physics & Electricity Vol. 3

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  Speaker 1: Section twenty seven The Science History of the Universe, Volume three.
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  Speaker 1: This is a LibriVox recording. All LibriVox recordings or in
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  Speaker 1: the public domain. For more information or to volunteer, please
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  Speaker 1: visit LibriVox dot org. The Science History of the Universe,
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  Speaker 1: Volume three, edited by Francis Rolt Wheeler Electricity, Chapter eight
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  Speaker 1: the telephone, Part two. In eighteen seventy seven, Emil Berliner
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  Speaker 1: of Washington, d C. Filed a caveat and later in
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  Speaker 1: the same year applied for a patent on a transmitter
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  Speaker 1: depending upon a principle pointed out in articles published in
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  Speaker 1: eighteen fifty six eighteen sixty four. In eighteen seventy four
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  Speaker 1: by the French scientist Dumont cell that if the pressure
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  Speaker 1: between two conducting bodies forming part of an electric circuit
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  Speaker 1: be increased, the resistance of the path between them will
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  Speaker 1: be diminished, and conversely, if the pressure between them be decreased,
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  Speaker 1: a corresponding increase of resistance will result. Berliner's transmitter is
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  Speaker 1: shown in principle in Fig. Thirty seven, which is a
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  Speaker 1: reproduction of the principal figure in his now famous patent.
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  Speaker 1: In this a is the vibratory diaphragm of metal against
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  Speaker 1: center of which rests the metal ball C, carried on
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  Speaker 1: a thumbscrew B, which is mounted in this standard D.
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  Speaker 1: The pressure of the ball C against the plate A
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  Speaker 1: can be regulated by turning the thumbscrew. The diaphragm and
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  Speaker 1: ball form the terminals or electrodes of a circuit, including
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  Speaker 1: a battery and receiving instrument. The action of this instrument,
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  Speaker 1: which at best has never been satisfactory or commercial, is
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  Speaker 1: as follows. When the diaphragm vibrates, the pressure at the
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  Speaker 1: point of contact A becomes greater or less, thus varying
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  Speaker 1: the resistance of the contact and causing corresponding undulations in
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  Speaker 1: the current flowing. Soon after this, Edison devised an instrument
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  Speaker 1: using carbon as the medium for varying the resistance of
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  Speaker 1: the circuit with changes of pressure. Edison's first type of
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  Speaker 1: carbon transmitter consisted simply of a button of compressed plumbago
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  Speaker 1: bearing against the small platinum disc secured to the diaphragm.
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  Speaker 1: The plumbago button was held against the diaphragm by a spring,
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  Speaker 1: the tension of which could be adjusted by a thumbscrew.
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  Speaker 1: A form of Edison's transmitter devised by George M. Phelps
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  Speaker 1: in eighteen seventy eight is shown in figure thirty eight.
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  Speaker 1: The transmitting device proper is shown in the small cut
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  Speaker 1: at the right of this figure, and is enclosed in
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  Speaker 1: a cup shaped case formed of the two pieces A
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  Speaker 1: and B as shown. Secure to the front of the
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  Speaker 1: enlarged head of the adjustment screw E is a thin
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  Speaker 1: platinum disc F, against which rests a cylindrical button G
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  Speaker 1: of compressed lamp black. A plate of glass I carrying
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  Speaker 1: a hemispherical button K has attached to its rear face
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  Speaker 1: another platinum disc H. This second platinum disc rests against
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  Speaker 1: the front face of the lamp black disc G, and
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  Speaker 1: the button K presses firmly against the center of the
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  Speaker 1: diaphragm D. The plates F and H form the terminals
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  Speaker 1: of the transmitter, and as the diaphragm D vibrates, it
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  Speaker 1: causes variations in the pressure and corresponding changes in the
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  Speaker 1: resistance of the circuit, thus producing the desired undulations of current.
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  Speaker 1: Professor David b Ues made a most valuable contrybution, tending
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  Speaker 1: towards the perfection of the battery transmitter. By a series
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  Speaker 1: of interesting experiments, he demonstrated conclusively that a loose contact
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  Speaker 1: between the electrodes, no matter of what substance they are composed,
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  Speaker 1: is far preferable than a firm, strong current. The apparatus
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  Speaker 1: used in one of his earlier experiments, made in eighteen
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  Speaker 1: seventy eight, is shown in Fig. Thirty nine, and consists
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  Speaker 1: simply of three wire nails, of which A and B
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  Speaker 1: formed the terminals of the circuit containing a battery and
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  Speaker 1: a receiving instrument. The circuit was completed by a third nail, C,
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  Speaker 1: which was laid loosely across the other two. Any vibrations
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  Speaker 1: in the air in the vicinity caused variations in the
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  Speaker 1: intimacy of contact between the nails and corresponding variations in
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  Speaker 1: the resistance of the circuit. This was a very inefficient
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  Speaker 1: form of transmitter, but it demonstrated the principle of loose
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  Speaker 1: contact very cleverly. It was found that carbon was, for
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  Speaker 1: various reasons, by far the most desirable substance for electrodes
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  Speaker 1: in the loose contact transmitter, and nothing has ever been
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  Speaker 1: found to approach it inefficiency and desirability. Another form of
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  Speaker 1: transmitter deviced by used and called by him, the microphone,
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  Speaker 1: is shown in Fig. Thirty nine. This consists of a
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  Speaker 1: small pencil of gas carbon A pointed at each end,
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  Speaker 1: and two blocks B and B of carbon fastened to
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  Speaker 1: a diaphragm or sounding board C. These blocks are hollowed
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  Speaker 1: out in such a manner as to loosely hold between
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  Speaker 1: them the pencil A. The blocks B and B form
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  Speaker 1: the terminals of the circuit. This instrument, though crude in form,
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  Speaker 1: is of marvelous delicacy, and is well termed microphoneatest, noises
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  Speaker 1: in the vicinity, and even those incapable of being heard
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  Speaker 1: by the ear alone, produce surprising effects in the receiving instrument.
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  Speaker 1: This particular form of instrument is in fact too delicate
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  Speaker 1: for ordinary use, as any jar or loud noise will
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  Speaker 1: cause the electrodes to break contact and produce deafening noises
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  Speaker 1: in the receiver. Nearly all carbon transmitters of today are
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  Speaker 1: of the loose contact type, this having entirely superseded the
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  Speaker 1: first form devised by Edison, which was then supposed to
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  Speaker 1: depend upon the actual resistance of a carbon block being
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  Speaker 1: changed under varying pressure. In speaking of Professor Hugh's work
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  Speaker 1: on loose contacts and the microphone, the Telephone Journal and
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  Speaker 1: Electrical Review, an English paper says in its issue of
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  Speaker 1: July one, eighteen seventy eight, quote the microphone is a
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  Speaker 1: striking illustration of the truth that in science, any phenomenon, whatever,
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  Speaker 1: may be turned to account. The trouble of one generation
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  Speaker 1: of scientists may be turned to the honor and service
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  Speaker 1: of the next. Electricians have long had sore reasons for
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  Speaker 1: regarding a bad contact as an unmitigated nuisance, the instrument
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  Speaker 1: of the evil one, with no conceivable good in it,
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  Speaker 1: and no conceivable purpose except to annoy and tempt them
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  Speaker 1: into wickedness, and an expression of hearty but ignominious emotion.
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  Speaker 1: Professor Use, however, has with a wizard's power, transformed this
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  Speaker 1: electrician's mane into a professional glory and a public boon. Verily,
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  Speaker 1: there is a soul of virtue in things evil unquote
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  Speaker 1: Professor Use, in an article in Nature June twenty seven,
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  Speaker 1: eighteen seventy eight, thus describes the condition necessary for microphonic action. Quote.
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  Speaker 1: If the pressure on the materials is not sufficient, we
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  Speaker 1: shall have a constant succession of interruptions of contact, and
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  Speaker 1: the galvanometer needle will indicate the fact. If the pressure
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  Speaker 1: on the materials is gradually increased, the tones will be
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  Speaker 1: loud but wanting in distinctness, the galvanometer indicating interruptions. As
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  Speaker 1: the pressure is still increased, the tone becomes clearer and
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  Speaker 1: the galvanometer will be stationary when a maximum of loudness
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  Speaker 1: and clearness is attained. If the pressure be further increased,
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  Speaker 1: the sounds become weaker, though very clear, and as the
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  Speaker 1: pressure is still further augmented, the sounds die out as
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  Speaker 1: if the speaker was talking and walking away at the
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  Speaker 1: same time, until a point is arrived at where there
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  Speaker 1: is complete silence. Only one radical improvement now remains to
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  Speaker 1: be recorded. In eighteen eighty one, Henry Huntings devised a
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  Speaker 1: transmitter wherein the ves variable resistance medium consisted of a
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  Speaker 1: mass of finely divided carbon granules held between two conducting plates.
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  Speaker 1: His transmitter is shown in Fig. Forty between the metal
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  Speaker 1: diaphragm A and a parallel conducting plate B, both of
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  Speaker 1: which are securely mounted in a case formed by the
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  Speaker 1: block D and a mouthpiece. F is a chamber filled
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  Speaker 1: with the fine granules of carbon C. The diaphragm A
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  Speaker 1: and the plate B form the terminals of the transmitter
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  Speaker 1: and the current from the battery must therefore flow through
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  Speaker 1: the mass of granular carbon c. When the diaphragm is
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  Speaker 1: caused to vibrate by sound waves, it is brought into
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  Speaker 1: a more or less intimate contact with the carbon granules
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  Speaker 1: and causes a varying pressure between them. The resistance offered
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  Speaker 1: by them to the current is thus varied, and the
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  Speaker 1: desired undulations in the current produced. This transmitter, instead of
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  Speaker 1: have ving one or a few points of variable contact,
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  Speaker 1: is seen to have a multitude of them. It can
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  Speaker 1: carry a larger current without heating and at the same
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  Speaker 1: time produce greater changes in its resistance than the forms
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  Speaker 1: previously devised, and no ordinary sound can cause a total
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  Speaker 1: break between the electrodes. These and other advantages have caused
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  Speaker 1: this type in one form or another, to largely displace
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  Speaker 1: all others. At first, the practice was to put the
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  Speaker 1: transmitter together with the receiver and battery directly in circuit
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  Speaker 1: with the line wire. With this arrangement, the changes produced
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  Speaker 1: in the resistance by the transmitter were small in comparison
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  Speaker 1: with the total resistance of the circuit, especially in the
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  Speaker 1: case of a long line, and the changes in current
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  Speaker 1: were therefore small. Edison remedied this difficulty by using an
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  Speaker 1: induction coil in connection with the transmitter. The induction coil
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  Speaker 1: used then and now is made as follows. Around a
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  Speaker 1: core formed of a bundle of soft iron wires is
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  Speaker 1: wound a few turns of comparatively heavy insulated copper wire.
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  Speaker 1: Outside of this, and entirely separated from it, is wound
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  Speaker 1: another coil, consisting of a great number of turns of
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  Speaker 1: fine wire, also of copper and insulated. The transmitter, together
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  Speaker 1: with the battery, is placed in a closed circuit with
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  Speaker 1: the coarse winding of a few turns, while the fine
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  Speaker 1: winding of many turns is included directly in circuit with
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  Speaker 1: the line wire and the receiving instrument. The coarse winding
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  Speaker 1: is usually termed the primary winding because it is associated
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  Speaker 1: with the primary source of current, the battery, while the
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  Speaker 1: fine winding is usually termed the secondary winding because the
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  Speaker 1: currents flowing in it at the transmitting station are secondary
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  Speaker 1: or induced currents. In coils of this kind, the coarse
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  Speaker 1: winding is almost invariably termed the primary for the above reason.
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  Speaker 1: Although many conditions exist in electrical work and in telephone work,
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  Speaker 1: where the high resistance winding is in reality the primary coil.
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  Speaker 1: The circuit arrangement spoken of is shown in Figure forty one,
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  Speaker 1: in which T is a transmitter, B a battery, pns
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  Speaker 1: primary and secondary windings, respectively, of an induction coil, L
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  Speaker 1: and L the line wires, and R the receiving instrument.
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  Speaker 1: It is well to state here that the usual way
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  Speaker 1: of indicating the primary and secondary of an induction coil
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  Speaker 1: and dirographic representation of electrical circuits is by an arrangement
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  Speaker 1: of two adjacent zigzag lines, as shown in Figure forty one.
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  Speaker 1: A current flowing in the primary winding of the induction
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  Speaker 1: coil produces a field of force in the surrounding space,
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  Speaker 1: and any changes caused by the transmitter in the strength
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  Speaker 1: of the current produce changes in the intensity of this field.
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  Speaker 1: As the secondary winding lies in this field, these changes will,
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  Speaker 1: by the laws of Faraday and Henry, cause currents to
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  Speaker 1: flow in the secondary winding and through the line wire
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  Speaker 1: to the receiving instrument. In good induction coils, the electromotive
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  Speaker 1: forces up in the secondary coil bear nearly the same
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  Speaker 1: ratio to the changes in electromotive force in the primary coil,
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  Speaker 1: as the number of turns, and the secondary bears to
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  Speaker 1: the number of turns in the primary. The use of
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  Speaker 1: the induction coil with the transmitter accomplishes two very important results. First,
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  Speaker 1: it enables the transmitter to operate in a circuit of
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  Speaker 1: very low resistance, so that the changes in the resistance
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  Speaker 1: produced by the transmitter bear a very large ratio to
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  Speaker 1: the total resistance of the circuit. This advantage is well
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  Speaker 1: illustrated by contrasting the two following cases. Suppose a transmitter
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  Speaker 1: capable of producing a change of resistance of one ome
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  Speaker 1: be placed directly in a lined circuit whose total resistance
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  Speaker 1: is one thousand oms. A change in the resistance of
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  Speaker 1: the transmitter of one ome will then change the total
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  Speaker 1: resistance of the circuit one one thousandth of its value,
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  Speaker 1: and the resulting change in the current flowing will be
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  Speaker 1: but one one thousandth of its value. On the other hand,
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  Speaker 1: suppose the same transmitter to be placed in a local
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  Speaker 1: circuit as above described, the total resistance of which circuit
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  Speaker 1: is five omes. The change of one ome in the
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  Speaker 1: transmitter will now produce a change of resistance of one
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  Speaker 1: fifth of the total resistance of the circuit and cause
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  Speaker 1: a change of one fifth of the total current flowing.
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  Speaker 1: It is thus seen that fluctuations in the current can
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  Speaker 1: be produced by a transmitter with the aid of an
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  Speaker 1: induction coil, which are many times greater than those produced
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  Speaker 1: by the same transmitter without the coil. The second advantage
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  Speaker 1: is that, by virtue of the small number of turns
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  Speaker 1: and the primary winding and the large number in the
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  Speaker 1: secondary winding of the inducting coil, the currents generated in
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  Speaker 1: the secondary are of a very high voltage as compared
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  Speaker 1: with those in the primary, thus enabling transmission to be
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  Speaker 1: effected over much greater length of line and over vastly
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  Speaker 1: higher resistances than would be possible if the transmitter were
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  Speaker 1: forced to vary the current flowing through the entire length
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  Speaker 1: of the line. Neither the telephone receiver nor the transmitter
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  Speaker 1: have undergone any radical changes since their early days. Various
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  Speaker 1: minor details have received the attention of engineers and inventors,
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  Speaker 1: but the magneto telephone is still the receiver and the
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  Speaker 1: variable resistances of the carbon contacts the means of transmission.
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  Speaker 1: The principal developments have been in the means of intercommunication.
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  Speaker 1: The growth of the telephone industry has been very rapid,
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  Speaker 1: and from being a luxury, the telephone has become a
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  Speaker 1: business necessity. The tendency has been toward the simplification of
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  Speaker 1: the subscriber's station and the improvement of the central office.
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  Speaker 1: The battery current for talking is now supplied in concentrated
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  Speaker 1: communities from the central station. Considerable trouble formerly was experienced
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  Speaker 1: through the deterioration of the battery at the subscribers station.
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  Speaker 1: The telegraph phone or the telephone or graph is an
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  Speaker 1: instrument which records magnetically sounds produced at a distance. It
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  Speaker 1: was originated by mister Paulson, a Danish inventor. Fig. Forty
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  Speaker 1: three shows the essential parts. Either a steel band is
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  Speaker 1: used or a long steel wire rolled from one drum
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  Speaker 1: to the other under the recording magnet, which receives the
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  Speaker 1: talking currents and engraves them magnetically upon the steel wire.
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  Speaker 1: To reproduce the message, it is only necessary to pass
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  Speaker 1: the steel wire under a reproducing magnet connected to a
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  Speaker 1: telephone receiver. The reproduction being very perfect, The message may
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  Speaker 1: be erased from the wire by means of the obliterating
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  Speaker 1: magnet supplied with an alternating current. End of Section twenty
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  Speaker 1: seven