Fig. 62. Accumulator GridsFig. 62.Accumulator Grids
Accumulator Plates.—The elements used for accumulator plates are red lead for the positive plates, and precipitated lead, or the well-known litharge, for the negative plates. Experience has shown that the best way to hold this material is by means of lead grids
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Fig. 62 shows the typical form of one of these grids. It is made of lead, cast or molded in one piece, usually square, as at A, with a wing or projection (B), at one margin, extending upwardly and provided with a hole (C). The grid is about a quarter of an inch thick.
The Grid.—The open space, called the grid, proper, comprises cross bars, integral with the plate, made in a variety of shapes. Fig.62shows three forms of constructing these bars or ribs, the object being to provide a form which will hold in the lead paste, which is pressed in so as to make a solid-looking plate when completed.
The Positive Plate.—The positive plate is made in the following manner: Make a stiff paste of red lead and sulphuric acid; using a solution, say, of one part of acid to two parts of water. The grid is laid on a flat surface and the paste forced into the perforations with a stiff knife or spatula. Turn over the grid so as to get the paste in evenly on both sides.
The grid is then stood on its edge, from 18 to 20 hours, to dry, and afterwards immersed in a concentrated solution of chloride of lime, so as to convert it into lead peroxide. When the action is complete it is thoroughly rinsed in cold water, and is ready to use.
The Negative Plate.—The negative plate isp. 85filled, in like manner, with precipitated lead. This lead is made by putting a strip of zinc into a standard solution of acetate of lead, and crystals will then form on the zinc. These will be very thin, and will adhere together, firmly, forming a porous mass. This, when saturated and kept under water for a short time, may be put into the openings of the negative plate.
Fig. 63. Assemblage of Accumulator PlatesFig. 63.Assemblage of Accumulator Plates
Connecting Up the Plates.—The next step is to put these plates in position to form a battery. In Fig.63is shown a collection of plates connected together
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For simplicity in illustrating, the cell is made up of glass, porcelain, or hard rubber, with five plates (A), A, A representing the negative and B, B the positive plates. A base of grooved strips (C, C) is placed in the batteries of the cell to receive the lower ends of the plates. The positive plates are held apart by means of a short section of tubing (D), which is clamped and held within the plates by a bolt (E), this bolt also being designed to hold the terminal strip (F).
In like manner, the negative plates are held apart by the two tubular sections (G), each of which is of the same length as the section D of the positives. The bolt (H) holds the negatives together as well as the terminal (I). The terminals should be lead strips, and it would be well, owing to the acid fumes which are formed, to coat all brass work, screws, etc., with paraffine wax.
The electrolyte or acid used in the cell, for working purposes, is a pure sulphuric acid, which should be diluted with about four times its weight in water. Remember, you should always add the strong acid to the water, and never pour the water into the acid, as the latter method causes a dangerous ebullition, and does not produce a good mixture
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Put enough of this solution into the cell to cover the tops of the plates, and the cell is ready.
Fig. 64. Connecting Up Storage Battery in SeriesFig. 64.Connecting Up Storage Battery in Series
Charging the Cells.—The charge of the current must never be less than 2.5 volts. Each cell has an output, in voltage, of about 2 volts, hence if we have, say, 10 cells, we must have at least 25 volts charging capacity. We may arrange these in one line, or in series, as it is called, so far as the connections are concerned, and charge them with a dynamo, or other electrical source, which shows a pressure of 25 volts, as illustrated in Fig.64, or, instead of this, we may put them into two parallel sets of 5 cells each, as shown in Fig.65, and use 12.5 volts to charge with. In this case it will take double the time because we are charging with only one-half the voltage used in the first case.
The positive pole of the dynamo should be connected with the positive pole of the accumulatorp. 88cell, and negative with negative. When this has been done run up the machine until it slightly exceeds the voltage of the cells. Thus, if we have 50 cells in parallel, like in Fig.64, at least 125 volts will be required, and the excess necessary should bring up the voltage in the dynamo to 135 or 140 volts.
Fig. 65. Parallel SeriesFig. 65.Parallel Series
Fig. 66. Charging CircuitFig. 66.Charging Circuit
The Initial Charge.—It is usual initially to charge the battery from periods ranging from 36 to 40 hours, and to let it stand for 12 or 15 hours, after which to re-charge, until the positive plates have turned to a chocolate color, and the negativep. 89plates to a slate or gray color, and both plates give off large bubbles of gas.
In charging, the temperature of the electrolyte should not exceed 100° Fahrenheit.
When using the accumulators they should never be fully discharged.
The Charging Circuit.—The diagram (Fig.66) shows how a charging circuit is formed. The lamps are connected up in parallel, as illustrated. Each 16-candle-power 105-volt lamp will carry ½ ampere, so that, supposing we have a dynamo which gives 110 volts, and we want to charge a 4-volt accumulator, there will be 5-volt surplus to go to the accumulator. If, for instance, you want the cell to have a charge of 2 amperes, four of these lamps should be connected up in parallel. If 3 amperes are required, use 6 lamps, and so on.
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The telegraph is a very simple instrument. The key is nothing more or less than a switch which turns the current on and off alternately.
The signals sent over the wires are simply the audible sounds made by the armature, as it moves to and from the magnets.
Mechanism in Telegraph Circuits.—A telegraph circuit requires three pieces of mechanism at each station, namely, a key used by the sender, a sounder for the receiver, and a battery.
The Sending Key.—The base of the sending instrument is six inches long, four inches wide, and three-quarters of an inch thick, made of wood, or any suitable non-conducting material. The key (A) is a piece of brass three-eighths by one-half inch in thickness and six inches long. Midway between its ends is a cross hole, to receive the pivot pin (B), which also passes through a pair of metal brackets (C, D), the bracket C having a screw to hold one of the line wires, and the other bracket having a metal switch (E) hinged thereto. This switch bar, like the brackets, is made ofp. 91brass, one-half inch wide by one-sixteenth of an inch thick.
Below the forward end of the key (A) is a cross bar of brass (F), screwed to the base by a screw at one end, to receive the other line wire. Directly below the key (A) is a screw (G), so that the key will strike it when moved downwardly. The other end of the bar (F) contacts with the forward end of the switch bar (E) when the latter is moved inwardly.
Fig. 67. Telegraph Sending KeyFig. 67.Telegraph Sending Key
The forward end of the key (A) has a knob (H) for the fingers, and the rear end has an elastic (I) attached thereto which is secured to the end of the base, so that, normally, the rear end is held against the base and away from the screw head (G). The head (J) of a screw projects from the base at its rear end. Key A contacts with it.
When the key A contacts with the screw headsp. 92G, J, a click is produced, one when the key is pressed down and the other when the key is released.
You will notice that the two plates C, F are connected up in circuit with the battery, so that, as the switch E is thrown, so as to be out of contact, the circuit is open, and may be closed either by the key A or the switch E. The use of the switch will be illustrated in connection with the sounder.
Fig. 68. Telegraph SounderFig. 68.Telegraph Sounder
When the key A is depressed, the circuit of course goes through plate C, key A and plate F to the station signalled.
The Sounder.—The sounder is the instrument which carries the electro-magnet.
In Fig.68this is shown in perspective. The base is six inches long and four inches wide, beingp. 93made, preferably, of wood. Near the forward end is mounted a pair of electro-magnets (A, A), with their terminal wires connected up with plates B, B', to which the line wires are attached.
Midway between the magnets and the rear end of the base is a pair of upwardly projecting brackets (C). Between these are pivoted a bar (D), the forward end of which rests between the magnets and carries, thereon, a cross bar (E) which is directly above the magnets, and serves as the armature.
The rear end of the base has a screw (F) directly beneath the bar D of such height that when the rear end of the bar D is in contact therewith the armature E will be out of contact with the magnet cores (A, A). A spiral spring (G) secured to the rear ends of the arm and to the base, respectively, serves to keep the rear end of the key normally in contact with the screw F.
Connecting Up the Key and Sounder.—Having made these two instruments, we must next connect them up in the circuit, or circuits, formed for them, as there must be a battery, a key, and a sounder at each end of the line.
In Fig.69you will note two groups of those instruments. Now observe how the wires connect them together. There are two line wires, one (A) which connects up the two batteries, the wirep. 94being attached so that one end connects with the positive terminal of the battery, and the other end with the negative terminal.
Fig. 69. A Telegraph CircuitFig. 69.A Telegraph Circuit
The other line wire (B), between the two stations, has its opposite ends connected with the terminals of the electro-magnet C of the sounders. The other terminals of each electro-magnet are connected up with one terminal of each key by a wire (D), and to complete the circuit at each station, the other terminal of the key has a wire (E) to its own battery.
Two Stations in Circuit.—The illustration shows station 2 telegraphing to station 1. This is indicated by the fact that the switch F' of that instrument is open, and the switch F of station 1 closed. When, therefore, the key of station 2 is depressed, a complete circuit is formedp. 95which transmits the current through wire E' and battery, through line A, then through the battery of station 1, through wire E to the key, and from the key, through wire D, to the sounder, and finally from the sounder over line wire B back to the sounder of station 2, completing the circuit at the key through wire D'.
When the operator at station 2 closes the switch F', and the operator at station 1 opens the switch F, the reverse operation takes place. In both cases, however, the sounder is in at both ends of the line, and only the circuit through the key is cut out by the switch F, or F'.
The Double Click.—The importance of the double click of the sounder will be understood when it is realized that the receiving operator must have some means of determining if the sounder has transmitted a dot or a dash. Whether he depresses the key for a dot or a dash, there must be one click when the key is pressed down on the screw head G (Fig.62), and also another click, of a different kind, when the key is raised up so that its rear end strikes the screw head J. This action of the key is instantly duplicated by the bar D (Fig.68) of the sounder, so that the sounder as well as the receiver knows the time between the first and the second click, and by that means he learns that a dot or a dash is made
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Illustrating the Dot and the Dash.—To illustrate: Let us suppose, for convenience, that the downward movement of the lever in the key, and the bar in the sounder, make a sharp click, and the return of the lever and bar make a dull click. In this case the ear, after a little practice, can learn readily how to distinguish the number of downward impulses that have been given to the key.
The Morse Telegraph Code
Morse Code Table: A-Z, 0-9, &
Example in Use.—Let us take an example in the word "electrical."
E L E C T R I C A L
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The operator first makes a dot, which means a sharp and a dull click close together; there is then a brief interval, then a lapse, after which there is a sharp click, followed, after a comparatively longer interval, with the dull click. Now a dash by itself may be an L, a T, or the figure 0, dependent upon its length. The short dash is T, and the longest dash the figure 0. The operator will soon learn whether it is either of these or the letter L, which is intermediate in length.
In time the sender as well as receiver will give a uniform length to the dash impulse, so that it may be readily distinguished. In the same way, we find that R, which is indicated by a dot, is followed, after a short interval, by two dots. This might readily be mistaken for the single dot for E and the two dots for I, were it not that the time element in R is not as long between the first and second dots, as it ordinarily is between the single dot of E when followed by the two dots of I.
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Induction.—One of the most remarkable things in electricity is the action of induction—that property of an electric current which enables it to pass from one conductor to another conductor through the air. Another singular and interesting thing is that the current so transmitted across spaces changes its direction of flow, and, furthermore, the tension of such a current may be changed by transmitting it from one conductor to another.
Low and High Tension.—In order to effect this latter change—that is, to convert it from a low tension to a high tension—coils are used, one coil being wound upon the other; one of these coils is called the primary and the other the secondary. The primary coil receives the current from the battery, or source of electrical power, and the secondary coil receives charges, and transmits the current.
For an illustration of this examine Fig.70, in which you will note a coil of heavy wire (A), around which is wound a coil of fine wire (B). If, for instance, the primary coil has a low voltage,p. 99the secondary coil will have a high voltage, or tension. Advantage is taken of this phase to use a few cells, as a primary battery, and then, by a set ofInduction Coils, as they are called, to build up a high-tension electro-motive force, so that the spark will jump across a gap, as shown at C, for the purpose of igniting the charges of gas in a gasoline motor; or the current may be used for medical batteries, and for other purposes.
Fig. 70. Induction Coil and CircuitFig. 70.Induction Coil and Circuit
The current passes, by induction, from the primary to the secondary coil. It passes from a large conductor to a small conductor, the small conductor having a much greater resistance than the large one.
Elastic Property of Electricity.—While electricity has no resiliency, like a spring, for instance, still it acts in the manner of a cushion under certain conditions. It may be likened to an oscillating spring acted upon by a bar
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Referring to Fig.71, we will assume that the bar A in falling down upon the spring B compresses the latter, so that at the time of greatest compression the bar goes down as far as the dotted line C. It is obvious that the spring B will throw the bar upwardly. Now, electricity appears to have a kind of elasticity, which characteristic is taken advantage of in order to increase the efficiency of the induction in the coil.
Fig. 71. Illustrating ElasticityFig. 71.Illustrating Elasticity
The Condenser.—To make a condenser, prepare two pine boards like A, say, eight by ten inches and a half inch thick, and shellac thoroughly on all sides. Then prepare sheets of tinfoil (B), six by eight inches in size, and also sheets of paraffined paper (C), seven by nine inches in dimensions. Also cut out from the waste pieces of tinfoil strips (D), one inch by two inches. To build up the condenser, lay down a sheet of paraffined paper (C), then a sheet of tinfoil (B),p. 101and before putting on the next sheet of paraffined paper lay down one of the small strips (D) of tinfoil, as shown in the illustration, so that its end projects over one end of the board A; then on the second sheet of paraffine paper lay another sheet of tinfoil, and on this, at the opposite end, place one of the small strips (D), and so on, using from 50 to 100 of the tinfoil sheets. When the last paraffine sheet is laid on, the other board is placed on top, and the whole bound together, either by wrapping cords around the same or by clamping them together with bolts.
Fig. 72. CondenserFig. 72.Condenser
You may now make a hole through the projecting ends of the strips, and you will have two sets of tinfoil sheets, alternately connected together at opposite ends of the condenser.
Care should be exercised to leave the paraffine sheets perfect or without holes. You can makep. 102these sheets yourself by soaking them in melted paraffine wax.
Connecting Up a Condenser.—When completed, one end of the condenser is connected up with one terminal of the secondary coil, and the other end of the condenser with the other secondary terminal.
Fig. 73. High-tension CircuitFig. 73.High-tension Circuit
In Fig.73a high-tension circuit is shown. Two coils, side by side, are always used to show an induction coil, and a condenser is generally shown, as illustrated, by means of a pair of forks, one resting within the other.
The Interrupter.—One other piece of mechanism is necessary, and that is anInterrupter, for the purpose of getting the effect of the pulsations given out by the secondary coil.
A simple current interrupter is made as follows: Prepare a wooden base (A), one inch thick, six inches wide, and twelve inches long. Upon this mount a toothed wheel (B), six inchesp. 103in diameter, of thin sheet metal, or a brass gear wheel will answer the purpose. The standard (C), which supports the wheel, may be of metal bent up to form two posts, between which the crankshaft (D) is journaled. The base of the posts has an extension plate (E), with a binding post for a wire. At the front end of the base is an L-shaped strip (F), with a binding post for a wire connection, and the upwardly projecting part of the strip contacts with the toothed wheel. When the wheel B is rotated the spring finger (F) snaps from one tooth to the next, so that, momentarily, the current is broken, and the frequency is dependent upon the speed imparted to the wheel.
Fig. 74. Current InterrupterFig. 74.Current Interrupter
Uses of High-tension Coils.—This high-tension coil is made use of, and is the essential apparatus in wireless telegraphy, as we shall see in the chapter treating upon that subject.
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Telegraphing Without Wires.—Wireless telegraphy is an outgrowth of the ordinary telegraph system. When Maxwell, and, later on, Hertz, discovered that electricity, magnetism, and light were transmitted through the ether, and that they differed only in their wave lengths, they laid the foundations for wireless telegraphy. Ether is a substance which is millions and millions of times lighter than air, and it pervades all space. It is so unstable that it is constantly in motion, and this phase led some one to suggest that if a proper electrical apparatus could be made, the ether would thereby be disturbed sufficiently so that its impulses would extend out a distance proportioned to the intensity of the electrical agitation thereby created.
Surging Character of High-tension Currents.—When a current of electricity is sent through a wire, hundreds of miles in length, the current surges back and forth on the wire many thousands of times a second. Light comes to us from the sun, over 90,000,000 of miles, through the ether. It is as reasonable to suppose, or infer,p. 105that the ether can, therefore, convey an electrical impulse as readily as does a wire.
It is on this principle that impulses are sent for thousands of miles, and no doubt they extend even farther, if the proper mechanism could be devised to detect movement of the waves so propagated.
The Coherer.—The instrument for detecting these impulses, or disturbances, in the ether is generally called acoherer, although detector is the term which is most satisfactory. The name coherer comes from the first practical instrument made for this purpose.
Fig. 75. Wireless Telegraphy CohererFig. 75.Wireless Telegraphy Coherer
How Made.—The coherer is simply a tube, say, of glass, within which is placed iron filings. When the oscillations surge through the secondary coil the pressure or potentiality of the current finally causes it to leap across the small space separating the filings and, as it were, it welds together their edges so that a current freely passes. Thep. 106bringing together of the particles, under these conditions, is called cohering.
Fig. 75 shows the simplest form of coherer. The posts (A) are firmly affixed to the base (B), each post having an adjusting screw (C) in its upper end, and these screw downwardly against and serve to bind a pair of horizontal rods (D), the inner ends of which closely approach each other. These may be adjusted so as to be as near together or as far apart as desired. E is a glass tube in which the ends of the rods (D) rest, and between the separated ends of the rods (D) the iron filings (F) are placed.
The Decoherers.—For the purpose of causing the metal filings to fall apart, or decohere, the tube is tapped lightly, and this is done by a little object like the clapper of an electric bell.
In practice, the coils and the parts directly connected with it are put together on one base.
The Sending Apparatus.—Fig.76shows a section of a coil with its connection in the sending station. The spark gap rods (A) may be swung so as to bring them closer together or farther apart, but they must not at any time contact with each other.
The induction coil has one terminal of the primary coil connected up by a wire (B) with one post of a telegraph key, and the other post ofp. 107the key has a wire connection (C), with one side of a storage battery. The other side of the battery has a wire (D) running to the other terminal of the primary.
Fig. 76. Wireless Sending ApparatusFig. 76.Wireless Sending Apparatus
The secondary coil has one of its terminals connected with a binding post (E). This binding post has an adjustable rod with a knob (F) on its end, and the other binding post (G), which is connected up with the other terminal of thep. 108secondary coil, carries a similar adjusting rod with a knob (H).
From the post (E) is a wire (I), which extends upwardly, and is called the aerial wire, or wire for the antennæ, and this wire also connects with one side of the condenser by a conductor (J). The ground wire (K) connects with the other binding post (G), and a branch wire (L) also connects the ground wire (K) with one end of the condenser.
Fig. 77. Wireless Receiving ApparatusFig. 77.Wireless Receiving Apparatus
The Receiving Apparatus.—The receiving station, on the other hand, has neither condenser, induction coil, nor key. When the apparatus is in operation, the coherer switch is closed, and the instant a current passes through the coherer and operates the telegraph sounder, the galvanometer indicates the current.
Of course, when the coherer switch is closed, the battery operates the decoherer
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How the Circuits are Formed.—By referring again to Fig.76, it will be seen that when the key is depressed, a circuit is formed from the battery through wire B to the primary coil, and back again to the battery through wire D. The secondary coil is thereby energized, and, when the full potential is reached, the current leaps across the gap formed between the two knobs (F, H), thereby setting up a disturbance in the ether which is transmitted through space in all directions.
It is this impulse, or disturbance, which is received by the coherer at the receiving station, and which is indicated by the telegraph sounder.
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Vibrations.—Every manifestation in nature is by way of vibration. The beating of the heart, the action of the legs in walking, the winking of the eyelid; the impulses from the sun, which we call light; sound, taste and color appeal to our senses by vibratory means, and, as we have hereinbefore stated, the manifestations of electricity and magnetism are merely vibrations of different wave lengths.
The Acoustic Telephone.—That sound is merely a product of vibrations may be proven in many ways. One of the earliest forms of telephones was simply a "sound" telephone, called theAcoustic Telephone. The principle of this may be illustrated as follows:
Take two cups (A, B), as in Fig.78, punch a small hole through the bottom of each, and run a string or wire (C) from the hole of one cup to that of the other, and secure it at both ends so it may be drawn taut. Now, by talking into the cup (A) the bottom of it will vibrate to and fro, as shown by the dotted lines and thereby cause the bottom of the other cup (B) to vibratep. 111in like manner, and in so vibrating it will receive not only the same amplitude, but also the same character of vibrations as the cup (A) gave forth.
Fig. 78. Acoustic TelephoneFig. 78.Acoustic Telephone
Fig. 79. Illustrating VibrationsFig. 79.Illustrating Vibrations
Sound Waves.—Sound waves are long and short; the long waves giving sounds which are low in the musical scale, and the short waves high musical tones. You may easily determine this by the following experiment:
Stretch a wire, as at B (Fig.79), fairly tight, and then vibrate it. The amplitude of the vibration will be as indicated by dotted line A. Now, stretch it very tight, as at C, so that the amplitude of vibration will be as shown at E. By putting your ear close to the string you will find that while A has a low pitch, C is very much higher. Thisp. 112is the principle on which stringed instruments are built. You will note that the wave length, which represents the distance between the dotted lines A is much greater than E.
Hearing Electricity.—In electricity, mechanism has been made to enable man to note the action of the current. By means of the armature, vibrating in front of a magnet, we can see its manifestations. It is now but a step to devise some means whereby we may hear it. In this, as in everything else electrically, the magnet comes into play.
Fig. 80 .The Magnetic FieldFig. 80.The Magnetic Field
In the chapter on magnetism, it was stated that the magnetic field extended out beyond the magnet, so that if we were able to see the magnetism, the end of a magnet would appear to us something like a moving field, represented by the dotted lines in Fig.80.
The magnetic field is shown in Fig.80at onlyp. 113one end, but its manifestations are alike at both ends. It will be seen that the magnetic field extends out to a considerable distance and has quite a radius of influence.
The Diaphragm in a Magnetic Field.—If, now, we put a diaphragm (A) in this magnetic field, close up to the end of the magnet, but not so close as to touch it, and then push it in and out, or talk into it so that the sound waves strike it, the movement or the vibration of the diaphragm (A) will disturb the magnetic field emanating from the magnet, and this disturbance of the magnetic field at one end of the magnet also affects the magnetic field at the other end in the same way, so that the disturbance there will be of the same amplitude. It will also display the same characteristics as did the magnetic field when the diaphragm (A) disturbed it.
A Simple Telephone Circuit.—From this simple fact grew the telephone. If two magnets are connected up in the same circuit, so that the magnetic fields of the two magnets have the same source of electric power, the disturbance of one diaphragm will affect the other similarly, just the same as the two magnetic fields of the single magnet are disturbed in unison.
How to Make a Telephone.—For experimental and testing purposes two of these telephonesp. 114should be made at the same time. The case or holder (A) may be made either of hard wood or hard rubber, so that it is of insulating material. The core (B) is of soft iron, ⅜ inch in diameter and 5 inches long, bored and threaded at one end to receive a screw (C) which passes through the end of the case (A).
The enlarged end of the case should be, exteriorly, 2¼ inches in diameter, and the body of the case 1 inch in diameter.
Fig. 81. Section of Telephone ReceiverFig. 81.Section of Telephone Receiver
Interiorly, the large end of the case is provided with a circular recess 1¾ inches in diameter and adapted to receive therein a spool which is, diametrically, a little smaller than the recess. The spool fits fairly tight upon the end of the core, and when in position rests against an annular shoulder in the recess. A hollow space (F) is thus provided behind the spool (D), so the two wiresp. 115from the magnet may have room where they emerge from the spool.
The spool is a little shorter than the distance between the shoulder (E) and the end of the casing, at G, and the core projects only a short distance beyond the end of the spool, so that when the diaphragm (H) is put upon the end of the case, and held there by screws (I) it will not touch the end of the core. A wooden or rubber mouthpiece (J) is then turned up to fit over the end of the case.
Fig. 82. The Magnet and Receiver HeadFig. 82.The Magnet and Receiver Head
The spool (D) is made of hard rubber, and is wound with No. 24 silk-covered wire, the windings to be well insulated from each other. The two ends of the wire are brought out, and threaded through holes (K) drilled longitudinally through the walls of the case, and affixed to the end by means of screws (L), so that the two wires may be brought together and connected with a duplex wire (M)
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As the screw (C), which holds the core in place, has its head hidden within a recess, which can be closed up by wax, the two terminals of the wires are well separated so that short-circuiting cannot take place.
Telephone Connections.—The simplest form of telephone connection is shown in Fig.83. This has merely the two telephones (A and B), with a single battery (C) to supply electricity for both. One line wire (D) connects the two telephones directly, while the other line (E) has the battery in its circuit.
Fig. 83. Simple Telephone ConnectionFig. 83.Simple Telephone Connection
Complete Installation.—To install a more complete system requires, at each end, a switch, a battery and an electro-magneto bell. You may use, for this purpose, a bell, made as shown in the chapter on bells.
Fig. 84 shows such a circuit. We now dispense with one of the line wires, because it has been found that the ground between the two stations serves as a conductor, so that only one line wire (A) is necessary to connect directly with the telephonesp. 117of the two stations. The telephones (B, B', respectively) have wires (C, C') running to the pivots of double-throw switches (D, D'), one terminal of the switches having wires (E, E'), which go to electric bells (F, F'), and from the bells are other wires (G, G'), which go to the ground. The ground wires also have wires (H, H'), which go to the other terminals of the switch (D, D'). The double-throw switch (D, D'), in the two stations, is thrown over so the current, if any should pass through, will go through the bell to the ground, through the wires (E, G or E', G').