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<v Speaker 1>Section twenty seven The Science History of the Universe, Volume three.

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<v Speaker 1>This is a LibriVox recording. All LibriVox recordings or in

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<v Speaker 1>the public domain. For more information or to volunteer, please

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<v Speaker 1>visit LibriVox dot org. The Science History of the Universe,

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<v Speaker 1>Volume three, edited by Francis Rolt Wheeler Electricity, Chapter eight

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<v Speaker 1>the telephone, Part two. In eighteen seventy seven, Emil Berliner

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<v Speaker 1>of Washington, d C. Filed a caveat and later in

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<v Speaker 1>the same year applied for a patent on a transmitter

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<v Speaker 1>depending upon a principle pointed out in articles published in

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<v Speaker 1>eighteen fifty six eighteen sixty four. In eighteen seventy four

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<v Speaker 1>by the French scientist Dumont cell that if the pressure

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<v Speaker 1>between two conducting bodies forming part of an electric circuit

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<v Speaker 1>be increased, the resistance of the path between them will

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<v Speaker 1>be diminished, and conversely, if the pressure between them be decreased,

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<v Speaker 1>a corresponding increase of resistance will result. Berliner's transmitter is

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<v Speaker 1>shown in principle in Fig. Thirty seven, which is a

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<v Speaker 1>reproduction of the principal figure in his now famous patent.

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<v Speaker 1>In this a is the vibratory diaphragm of metal against

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<v Speaker 1>center of which rests the metal ball C, carried on

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<v Speaker 1>a thumbscrew B, which is mounted in this standard D.

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<v Speaker 1>The pressure of the ball C against the plate A

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<v Speaker 1>can be regulated by turning the thumbscrew. The diaphragm and

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<v Speaker 1>ball form the terminals or electrodes of a circuit, including

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<v Speaker 1>a battery and receiving instrument. The action of this instrument,

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<v Speaker 1>which at best has never been satisfactory or commercial, is

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<v Speaker 1>as follows. When the diaphragm vibrates, the pressure at the

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<v Speaker 1>point of contact A becomes greater or less, thus varying

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<v Speaker 1>the resistance of the contact and causing corresponding undulations in

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<v Speaker 1>the current flowing. Soon after this, Edison devised an instrument

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<v Speaker 1>using carbon as the medium for varying the resistance of

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<v Speaker 1>the circuit with changes of pressure. Edison's first type of

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<v Speaker 1>carbon transmitter consisted simply of a button of compressed plumbago

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<v Speaker 1>bearing against the small platinum disc secured to the diaphragm.

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<v Speaker 1>The plumbago button was held against the diaphragm by a spring,

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<v Speaker 1>the tension of which could be adjusted by a thumbscrew.

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<v Speaker 1>A form of Edison's transmitter devised by George M. Phelps

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<v Speaker 1>in eighteen seventy eight is shown in figure thirty eight.

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<v Speaker 1>The transmitting device proper is shown in the small cut

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<v Speaker 1>at the right of this figure, and is enclosed in

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<v Speaker 1>a cup shaped case formed of the two pieces A

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<v Speaker 1>and B as shown. Secure to the front of the

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<v Speaker 1>enlarged head of the adjustment screw E is a thin

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<v Speaker 1>platinum disc F, against which rests a cylindrical button G

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<v Speaker 1>of compressed lamp black. A plate of glass I carrying

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<v Speaker 1>a hemispherical button K has attached to its rear face

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<v Speaker 1>another platinum disc H. This second platinum disc rests against

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<v Speaker 1>the front face of the lamp black disc G, and

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<v Speaker 1>the button K presses firmly against the center of the

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<v Speaker 1>diaphragm D. The plates F and H form the terminals

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<v Speaker 1>of the transmitter, and as the diaphragm D vibrates, it

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<v Speaker 1>causes variations in the pressure and corresponding changes in the

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<v Speaker 1>resistance of the circuit, thus producing the desired undulations of current.

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<v Speaker 1>Professor David b Ues made a most valuable contrybution, tending

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<v Speaker 1>towards the perfection of the battery transmitter. By a series

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<v Speaker 1>of interesting experiments, he demonstrated conclusively that a loose contact

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<v Speaker 1>between the electrodes, no matter of what substance they are composed,

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<v Speaker 1>is far preferable than a firm, strong current. The apparatus

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<v Speaker 1>used in one of his earlier experiments, made in eighteen

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<v Speaker 1>seventy eight, is shown in Fig. Thirty nine, and consists

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<v Speaker 1>simply of three wire nails, of which A and B

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<v Speaker 1>formed the terminals of the circuit containing a battery and

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<v Speaker 1>a receiving instrument. The circuit was completed by a third nail, C,

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<v Speaker 1>which was laid loosely across the other two. Any vibrations

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<v Speaker 1>in the air in the vicinity caused variations in the

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<v Speaker 1>intimacy of contact between the nails and corresponding variations in

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<v Speaker 1>the resistance of the circuit. This was a very inefficient

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<v Speaker 1>form of transmitter, but it demonstrated the principle of loose

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<v Speaker 1>contact very cleverly. It was found that carbon was, for

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<v Speaker 1>various reasons, by far the most desirable substance for electrodes

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<v Speaker 1>in the loose contact transmitter, and nothing has ever been

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<v Speaker 1>found to approach it inefficiency and desirability. Another form of

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<v Speaker 1>transmitter deviced by used and called by him, the microphone,

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<v Speaker 1>is shown in Fig. Thirty nine. This consists of a

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<v Speaker 1>small pencil of gas carbon A pointed at each end,

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<v Speaker 1>and two blocks B and B of carbon fastened to

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<v Speaker 1>a diaphragm or sounding board C. These blocks are hollowed

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<v Speaker 1>out in such a manner as to loosely hold between

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<v Speaker 1>them the pencil A. The blocks B and B form

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<v Speaker 1>the terminals of the circuit. This instrument, though crude in form,

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<v Speaker 1>is of marvelous delicacy, and is well termed microphoneatest, noises

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<v Speaker 1>in the vicinity, and even those incapable of being heard

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<v Speaker 1>by the ear alone, produce surprising effects in the receiving instrument.

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<v Speaker 1>This particular form of instrument is in fact too delicate

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<v Speaker 1>for ordinary use, as any jar or loud noise will

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<v Speaker 1>cause the electrodes to break contact and produce deafening noises

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<v Speaker 1>in the receiver. Nearly all carbon transmitters of today are

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<v Speaker 1>of the loose contact type, this having entirely superseded the

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<v Speaker 1>first form devised by Edison, which was then supposed to

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<v Speaker 1>depend upon the actual resistance of a carbon block being

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<v Speaker 1>changed under varying pressure. In speaking of Professor Hugh's work

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<v Speaker 1>on loose contacts and the microphone, the Telephone Journal and

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<v Speaker 1>Electrical Review, an English paper says in its issue of

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<v Speaker 1>July one, eighteen seventy eight, quote the microphone is a

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<v Speaker 1>striking illustration of the truth that in science, any phenomenon, whatever,

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<v Speaker 1>may be turned to account. The trouble of one generation

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<v Speaker 1>of scientists may be turned to the honor and service

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<v Speaker 1>of the next. Electricians have long had sore reasons for

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<v Speaker 1>regarding a bad contact as an unmitigated nuisance, the instrument

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<v Speaker 1>of the evil one, with no conceivable good in it,

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<v Speaker 1>and no conceivable purpose except to annoy and tempt them

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<v Speaker 1>into wickedness, and an expression of hearty but ignominious emotion.

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<v Speaker 1>Professor Use, however, has with a wizard's power, transformed this

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<v Speaker 1>electrician's mane into a professional glory and a public boon. Verily,

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<v Speaker 1>there is a soul of virtue in things evil unquote

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<v Speaker 1>Professor Use, in an article in Nature June twenty seven,

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<v Speaker 1>eighteen seventy eight, thus describes the condition necessary for microphonic action. Quote.

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<v Speaker 1>If the pressure on the materials is not sufficient, we

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<v Speaker 1>shall have a constant succession of interruptions of contact, and

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<v Speaker 1>the galvanometer needle will indicate the fact. If the pressure

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<v Speaker 1>on the materials is gradually increased, the tones will be

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<v Speaker 1>loud but wanting in distinctness, the galvanometer indicating interruptions. As

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<v Speaker 1>the pressure is still increased, the tone becomes clearer and

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<v Speaker 1>the galvanometer will be stationary when a maximum of loudness

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<v Speaker 1>and clearness is attained. If the pressure be further increased,

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<v Speaker 1>the sounds become weaker, though very clear, and as the

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<v Speaker 1>pressure is still further augmented, the sounds die out as

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<v Speaker 1>if the speaker was talking and walking away at the

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<v Speaker 1>same time, until a point is arrived at where there

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<v Speaker 1>is complete silence. Only one radical improvement now remains to

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<v Speaker 1>be recorded. In eighteen eighty one, Henry Huntings devised a

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<v Speaker 1>transmitter wherein the ves variable resistance medium consisted of a

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<v Speaker 1>mass of finely divided carbon granules held between two conducting plates.

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<v Speaker 1>His transmitter is shown in Fig. Forty between the metal

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<v Speaker 1>diaphragm A and a parallel conducting plate B, both of

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<v Speaker 1>which are securely mounted in a case formed by the

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<v Speaker 1>block D and a mouthpiece. F is a chamber filled

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<v Speaker 1>with the fine granules of carbon C. The diaphragm A

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<v Speaker 1>and the plate B form the terminals of the transmitter

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<v Speaker 1>and the current from the battery must therefore flow through

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<v Speaker 1>the mass of granular carbon c. When the diaphragm is

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<v Speaker 1>caused to vibrate by sound waves, it is brought into

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<v Speaker 1>a more or less intimate contact with the carbon granules

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<v Speaker 1>and causes a varying pressure between them. The resistance offered

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<v Speaker 1>by them to the current is thus varied, and the

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<v Speaker 1>desired undulations in the current produced. This transmitter, instead of

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<v Speaker 1>have ving one or a few points of variable contact,

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<v Speaker 1>is seen to have a multitude of them. It can

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<v Speaker 1>carry a larger current without heating and at the same

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<v Speaker 1>time produce greater changes in its resistance than the forms

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<v Speaker 1>previously devised, and no ordinary sound can cause a total

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<v Speaker 1>break between the electrodes. These and other advantages have caused

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<v Speaker 1>this type in one form or another, to largely displace

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<v Speaker 1>all others. At first, the practice was to put the

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<v Speaker 1>transmitter together with the receiver and battery directly in circuit

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<v Speaker 1>with the line wire. With this arrangement, the changes produced

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<v Speaker 1>in the resistance by the transmitter were small in comparison

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<v Speaker 1>with the total resistance of the circuit, especially in the

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<v Speaker 1>case of a long line, and the changes in current

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<v Speaker 1>were therefore small. Edison remedied this difficulty by using an

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<v Speaker 1>induction coil in connection with the transmitter. The induction coil

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<v Speaker 1>used then and now is made as follows. Around a

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<v Speaker 1>core formed of a bundle of soft iron wires is

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<v Speaker 1>wound a few turns of comparatively heavy insulated copper wire.

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<v Speaker 1>Outside of this, and entirely separated from it, is wound

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<v Speaker 1>another coil, consisting of a great number of turns of

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<v Speaker 1>fine wire, also of copper and insulated. The transmitter, together

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<v Speaker 1>with the battery, is placed in a closed circuit with

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<v Speaker 1>the coarse winding of a few turns, while the fine

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<v Speaker 1>winding of many turns is included directly in circuit with

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<v Speaker 1>the line wire and the receiving instrument. The coarse winding

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<v Speaker 1>is usually termed the primary winding because it is associated

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<v Speaker 1>with the primary source of current, the battery, while the

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<v Speaker 1>fine winding is usually termed the secondary winding because the

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<v Speaker 1>currents flowing in it at the transmitting station are secondary

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<v Speaker 1>or induced currents. In coils of this kind, the coarse

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<v Speaker 1>winding is almost invariably termed the primary for the above reason.

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<v Speaker 1>Although many conditions exist in electrical work and in telephone work,

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<v Speaker 1>where the high resistance winding is in reality the primary coil.

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<v Speaker 1>The circuit arrangement spoken of is shown in Figure forty one,

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<v Speaker 1>in which T is a transmitter, B a battery, pns

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<v Speaker 1>primary and secondary windings, respectively, of an induction coil, L

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<v Speaker 1>and L the line wires, and R the receiving instrument.

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<v Speaker 1>It is well to state here that the usual way

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<v Speaker 1>of indicating the primary and secondary of an induction coil

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<v Speaker 1>and dirographic representation of electrical circuits is by an arrangement

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<v Speaker 1>of two adjacent zigzag lines, as shown in Figure forty one.

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<v Speaker 1>A current flowing in the primary winding of the induction

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<v Speaker 1>coil produces a field of force in the surrounding space,

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<v Speaker 1>and any changes caused by the transmitter in the strength

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<v Speaker 1>of the current produce changes in the intensity of this field.

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<v Speaker 1>As the secondary winding lies in this field, these changes will,

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<v Speaker 1>by the laws of Faraday and Henry, cause currents to

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<v Speaker 1>flow in the secondary winding and through the line wire

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<v Speaker 1>to the receiving instrument. In good induction coils, the electromotive

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<v Speaker 1>forces up in the secondary coil bear nearly the same

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<v Speaker 1>ratio to the changes in electromotive force in the primary coil,

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<v Speaker 1>as the number of turns, and the secondary bears to

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<v Speaker 1>the number of turns in the primary. The use of

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<v Speaker 1>the induction coil with the transmitter accomplishes two very important results. First,

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<v Speaker 1>it enables the transmitter to operate in a circuit of

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<v Speaker 1>very low resistance, so that the changes in the resistance

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<v Speaker 1>produced by the transmitter bear a very large ratio to

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<v Speaker 1>the total resistance of the circuit. This advantage is well

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<v Speaker 1>illustrated by contrasting the two following cases. Suppose a transmitter

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<v Speaker 1>capable of producing a change of resistance of one ome

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<v Speaker 1>be placed directly in a lined circuit whose total resistance

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<v Speaker 1>is one thousand oms. A change in the resistance of

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<v Speaker 1>the transmitter of one ome will then change the total

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<v Speaker 1>resistance of the circuit one one thousandth of its value,

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<v Speaker 1>and the resulting change in the current flowing will be

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<v Speaker 1>but one one thousandth of its value. On the other hand,

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<v Speaker 1>suppose the same transmitter to be placed in a local

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<v Speaker 1>circuit as above described, the total resistance of which circuit

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<v Speaker 1>is five omes. The change of one ome in the

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<v Speaker 1>transmitter will now produce a change of resistance of one

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<v Speaker 1>fifth of the total resistance of the circuit and cause

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<v Speaker 1>a change of one fifth of the total current flowing.

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<v Speaker 1>It is thus seen that fluctuations in the current can

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<v Speaker 1>be produced by a transmitter with the aid of an

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<v Speaker 1>induction coil, which are many times greater than those produced

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<v Speaker 1>by the same transmitter without the coil. The second advantage

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<v Speaker 1>is that, by virtue of the small number of turns

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<v Speaker 1>and the primary winding and the large number in the

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<v Speaker 1>secondary winding of the inducting coil, the currents generated in

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<v Speaker 1>the secondary are of a very high voltage as compared

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<v Speaker 1>with those in the primary, thus enabling transmission to be

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<v Speaker 1>effected over much greater length of line and over vastly

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<v Speaker 1>higher resistances than would be possible if the transmitter were

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<v Speaker 1>forced to vary the current flowing through the entire length

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<v Speaker 1>of the line. Neither the telephone receiver nor the transmitter

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<v Speaker 1>have undergone any radical changes since their early days. Various

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<v Speaker 1>minor details have received the attention of engineers and inventors,

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<v Speaker 1>but the magneto telephone is still the receiver and the

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<v Speaker 1>variable resistances of the carbon contacts the means of transmission.

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<v Speaker 1>The principal developments have been in the means of intercommunication.

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<v Speaker 1>The growth of the telephone industry has been very rapid,

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<v Speaker 1>and from being a luxury, the telephone has become a

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<v Speaker 1>business necessity. The tendency has been toward the simplification of

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<v Speaker 1>the subscriber's station and the improvement of the central office.

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<v Speaker 1>The battery current for talking is now supplied in concentrated

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<v Speaker 1>communities from the central station. Considerable trouble formerly was experienced

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<v Speaker 1>through the deterioration of the battery at the subscribers station.

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<v Speaker 1>The telegraph phone or the telephone or graph is an

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<v Speaker 1>instrument which records magnetically sounds produced at a distance. It

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<v Speaker 1>was originated by mister Paulson, a Danish inventor. Fig. Forty

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<v Speaker 1>three shows the essential parts. Either a steel band is

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<v Speaker 1>used or a long steel wire rolled from one drum

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<v Speaker 1>to the other under the recording magnet, which receives the

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<v Speaker 1>talking currents and engraves them magnetically upon the steel wire.

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<v Speaker 1>To reproduce the message, it is only necessary to pass

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<v Speaker 1>the steel wire under a reproducing magnet connected to a

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<v Speaker 1>telephone receiver. The reproduction being very perfect, The message may

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<v Speaker 1>be erased from the wire by means of the obliterating

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<v Speaker 1>magnet supplied with an alternating current. End of Section twenty

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<v Speaker 1>seven