The Standard Electrical Dictionary - A Popular Dictionary of Words and Terms Used in the Practice - of Electrical Engineering
by T. O'Conor Slone
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Switch Board. A board or tablet to which wires are led connecting with cross bars or other switching devices, so as to enable connections among themselves or with other circuits to be made.

Switch, Circuit Changing. A switch whose arm in its swing breaks one contact and swinging over makes another. It is employed to change the connections of circuits from one dynamo to another.

Synonyms—Changing Switch—Changing Over Switch.

Switch, Double Break. A form of switch in which double contact pieces are provided to give a better contact. One form consists of a hinged bar whose end swings down between two pairs of springs. Both pairs are connected to one terminal, and the bar to the other terminal of a circuit.

Switch, Double Pole. A heavy switch for central station work, that connects and disconnects two leads simultaneously.

Switch, Feeder. A heavy switch, often of double contact type, for connecting and disconnecting feeders from bus bars in central stations.


Switch, Knife. A switch whose movable arm is a narrow, deep bar of copper or brass, and which in making contact is forced in edgeways between two springs connected to one terminal. The bar is connected to the other terminal.

Synonyms—Knife Break Switch—Knife Edge Switch.

Switch, Multiple. A switch which in the swing of its bar connects one by one with a number of contacts so that ultimately the end of its bar is in contact with all at once. It is used to throw lights in and out in succession, and it can, if the multiple contacts connect with resistances, make them operate as a rheostat.

Switch, Pole Changing. A switch for changing the direction of the current in a circuit.

Switch, Reversing. A switch, often of the plug type (see Plug Switch) for changing the direction of current passing through a galvanometer.

Switch, Snap. A switch constructed to give a quick, sharp break. It has a spiral spring interposed between the handle and arm. As the handle is drawn back to open it the spring is first extended, the bar being held by the friction of the contacts, until the spring suddenly jerks it up, thus breaking the contact.

Switch, Storage Battery Changing. A switch for changing storage battery connections from series to multiple and back again.

Switch, Three Way. A switch, so constructed that by turning its handle connection can be made from one lead to either of two other leads, and also so that connection can be completely cut off.

Sympathetic Vibration. The establishment of periodic movement in one body by impulses of the same period communicated to it from another body in motion. Thus if two tuning forks are of the same pitch and one is sounded the other will begin to sound by sympathy, the sound waves communicating the necessary periodic impulses to it.

Sympathetic vibrations are utilized in harmonic telegraphy. (See Harmonic Receiver—Telegraph, Harmonic.)

T. Symbol of time.

Tailings. (a) In high speed transmission of telegraph signals by the automatic system, the definiteness of the signal marks is sometimes interfered with by retardation. Wrong marks are thus produced called tailings.

(b) The prolongation of the current at the distant receiving station of a telegraph line due to the discharge of the line and to self-induction.

Synonyms—Tailing—Tailing Current.


Tamidine. Reduced nitro-cellulose. Nitro-cellulose is dissolved in a proper solvent and is obtained by evaporation as a translucent solid mass. By ammonium sulphide or other reagent it is reduced so as to be virtually cellulose. It is cut into shape for filaments of incandescent lamps, which shapes are carbonized and flashed.

Tangent Law. In a galvanometer the tangents of the angles of deflection of the needle are proportional to the deflecting force—

I. When the controlling force is unaltered in absolute magnitude and direction by the motion of the needle.

II. When the deflecting force acts at right angles always to the controlling force.

These conditions are usually secured by having the actuating coil through which the current passes flat and of large diameter compared to the length of the needle; by using the uniform field of the earth as the control; by having a short needle; by placing the coil with its plane in the magnetic meridian.

For best proportions of tangent galvanometer coils see Bobbins.


Tangent Scale. An arc of a circle in which the number of graduations in any arc starting from zero are proportional to the tangent of the angle subtended by such arc. The system is for use with tangent galvanometers. Thus if for 45 a value of 100 is taken and marked on the scale then for the arc 26 33' + a value of 50 should be marked on the scale because such are the relative values of the tangents.

Thus the scale instead of being divided into degrees is divided into arcs of varying length, growing shorter as they are more distant from the zero point, of such length that the first division being subtended by a tangent of length 1, the first and second divisions added or taken together as one arc are subtended by a tangent of length 2, and so on.

In the cut a simple method of graphically laying out a tangent scale is shown. In it C is the centre of the arc, and H the radius running to the zero of the instrument. From C a circle is described and on H a vertical line tangent to the arc is erected. Taking any part of the tangent, as the length shown ending at D, it is divided into any number of equal parts. Radii of the circle are now drawn whose prolongations pass through the divisions on the tangent. These radii, where they intersect the arc of the circle, determine equal divisions of the tangent scale, which, as is evident from the construction, are unequal angular divisions of the arc.


Tanning, Electric. The tanning of hides in the manufacture of leather by the aid of electrolysis. A current of electricity is maintained through the tanning vats in which regular tanning liquor is contained. Very extraordinary claims are made for the saving of time in the tanning process. What is ordinarily a process of several months, and sometimes of a year, is said to be reduced to one occupying a few days only. The action of electrolysis is the one relied on to explain the results.

Tapper. The key used in single needle telegraph transmitters. It comprises two flat springs L, E, each with a handle, normally pressed upward against one contact bar Z, and when pressed down by the operator making contact against a lower bar C when messages are to be transmitted. A double tapper, such as shown, is used for each instrument.

Synonyms—Double Tapper Key—Pedal Key.

Fig. 311. TAPPER.

Target, Electric. A target registering or indicating electrically upon an annunciator the point of impact of each bullet.

Taste, Galvanic. The effect produced upon the gustatory nerves by the passage of an electric current, or by the maintenance of potential difference between two portions of the tongue. It is very simply produced by placing a silver coin above, and a piece of zinc below the tongue, or the reverse, and touching their edges. A sour, peculiar taste is at once perceived. It cannot be due to any measurable quantity of current or of electrolytic decomposition, because the couple can do little more than establish a potential difference. With a strong current the taste becomes too strong for comfort, and if on a telegraph line the extra currents produced by the signaling make the operation of tasting the current a very unpleasant one. It is said that messages have been received in this way, the receiver placing one terminal of the line on his tongue, and a terminal attached to a grounded wire below it, and then receiving the Morse characters by taste.


Teazer. Originally a fine wire coil wound on the field magnets of a dynamo in shunt with the regular winding to maintain the magnetism. It was originally used in electroplating machines to prevent inversion of the magnetism, but has since developed into a component part of the winding of the compound dynamo. (See Dynamo, Compound.)

Tee, Lead. A lead pipe of T shape used for connecting branches to electric cables. The tee is soldered by wiped joints to the lead sheathings of the cable and branches after the wires have been connected, and the junctions coated with insulating tape or cement, or both.

It is sometimes made in two halves, and is known as a split tee.

Tel-autograph. A telegraph for reproducing the hand-writing of the sender at the receiving end of the line. To save time a special spelling is sometimes used.

Teleautograph. The special spelling used with the Tel-Autograph telegraph.

Tele-barometer, Electric. A barometer with electric attachment for indicating or recording at a distance the barometric readings.

Telegraph, ABC. This term is applied to alphabet telegraphs indicating the message by the movements of a pointer on a dial marked with the characters to be sent. In England the Wheatstone ABC system is much employed.

Telegraph, Automatic. A telegraph system based on the operation of the transmitting instrument by a perforated strip of paper drawn through it. The perforations made by an apparatus termed a perforator, are so arranged as to give telegraphic characters of the Morse or International Code in the transmitting instrument. (See Perforator.) Bain in the year 1846 was the originator of the system. He punched a fillet of paper with dots and dashes, and drew it between two terminals of the line, thus sending over the line a corresponding series of short and long currents which were received by his chemical receiver. (See Chemical Receiver.) The method was not successful. Its modern development, the Wheatstone Automatic Telegraph, is highly so. The perforated paper by its perforations controls the reciprocating movement of two rods, which pass through each hole in two rows, corresponding to the two rods respectively as the holes come opposite to the ends of the rods. The rods are kept constantly moving up and down. If unperforated paper is above them their upward motion is limited. This gives three positions for the rods, (a) both down, (b) one up and the other down, (c) both up. These positions of the rods work a pole changing key by which dots, spaces, and dashes are transmitted to the receiving instrument, which is an exceedingly delicate ink-printer. The latter can have its speed adjusted to receive from 200 to 450 words per minute.


Telegraph, Dial. A telegraph in which as receiver a dial instrument is used. A pointer or index hand moves around a dial. The dial is marked with letters of the alphabet. The movements of the pointer are controlled by the transmitting operator at a distant station. He by the same actions moves a pointer on a duplicate instrument before him and the two are synchronized to give identical indications. Thus a message is spelled out letter by letter on both dials simultaneously. The motions of the index are generally produced by what is virtually a recoil escapement. The scape wheel is carried by the axle of the index, and a pallet or anchor is vibrated by an electro-magnet whose armature is attached to the stem of the pallet. As the pallet is vibrated it turns the wheel and index one tooth for each single movement. There are as many teeth in the wheel as there are characters on the dial. The two instruments being in duplicate and synchronized, the pallets move exactly in unison, so that identical readings of the dials are given. The pallets may be moved by any kind of make and break mechanism, such as an ordinary telegraph key. The index moves by steps or jerks, so that the system is sometimes called step-by-step telegraphy.


In the cut the make and break transmitter is shown at v v, with its handle and contacts g and t. This mechanism sends impulses of current by F and Z to the receiving magnet l. This attracts and releases its armature K from contact into the position indicated by the dotted lines. This works the rocker n on the pin o, and actuates the double or anchor pawl s r, which turns the pallet or scrape wheel m.

The system is dropping into disuse, being supplanted by the telephone.

Synonym—Step-by-step Telegraph.


Telegraph, Double Needle. A telegraph system in which the message is read by the motions of two vertical needles on the face of the instrument in front of the receiving operator. An identical instrument faces the transmitting operator. By two handles, one for each hand, the needles are caused by electric impulses to swing to right and to left so as to give a telegraphic code. It has been generally superseded by the single needle telegraph.

Telegraph, Duplex. A telegraph capable of transmitting simultaneously two messages over one wire. The methods of effecting it are distinct from those of multiplex telegraphy. This term is used as a distinction from diode multiplex telegraphy, in which the work is done on other principles. There are two systems of duplex telegraphy, the differential and the bridge systems.

Telegraph, Duplex Bridge. A system of duplex telegraphy employing the principle of the Wheatstone bridge. The other or differential system depends on equality or difference of currents; the bridge method on equality or difference of potentials. The cut shows the system known as Steam's Plan.

At the ends of the line wire are two cross connections like duplicate galvanometer connections in a Wheatstone bridge, each including a receiving relay. The rest of the connections are self-explanatory.

When A depresses his key the current splits at the point indicating the beginning of the bridge. One portion goes through the line to B and to earth, the other goes to earth at A through the rheostats indicated by the corrugated lines.

On reaching B's end the current divides at the cross-connection and part goes through the receiving relay shown in the center of that cross-connection.

Thus if A sends to B or B to A it is without effect on the home receiving instrument. Now suppose that both simultaneously are sending in opposite directions. If the connections be studied it will be seen that every movement of the transmitting key will affect the balance of the distant or receiving end of the bridge and so its instrument will record the signals as they are sent.

As shown in the cut the sending keys are on local circuits, and work what are known as duplex transmitters. These are instruments which send line signals without breaking the connection.


In Stearn's plan condensers are introduced as shown. By this plan different receiving instruments can be used. The inventor once worked a Morse instrument at one end of the line, and a Hughes' instrument at the other end.


Telegraph, Duplex, Differential. A system of duplex telegraphy employing the differential action of two exciting or magnetizing coils. The general principles are the following. Suppose that at each of two stations, there is a magnet working as a sounder or relay. Each magnet is differentially wound, with two coils of opposite direction, of identical number of turns.

When the sending key at a station A is depressed two exactly equal currents go through the magnet in opposite directions. One called the compensation current goes to the earth at the stations. The other called the line current goes through the line, through the line coil of the distant station E, thereby actuating the relay or sounder armature.

The instrument of the sender A is unaffected because he is sending opposite and equal currents through its two coils. A special resistance is provided on the compensation circuit for keeping the currents exactly equal in effect. Nothing the sender at A does affects his own instrument.

Now suppose E desires to telegraph back at the same time that A is telegraphing to his station. He works his key. This does not affect his own instrument except by sending the equal and opposite currents through its coils. When his key is depressed and A's key is untouched, he works A's receiving instrument.


When A's key is depressed simultaneously with B's key, the two line currents are in opposition and neutralize each other. This throws out the balance in the instruments and both armatures are attracted by the compensation currents left free to act by the neutralization of the line currents.


Suppose that B is sending a dash, and it begins while A's key is raised. The line and compensation currents in B's receiving instrument neutralize each other and no effect is produced, while A's receiving instrument begins to register or indicate a dash. Now suppose A starts to send a dash while B's is half over. He depresses his key. This sends the two opposite currents through his magnet. His line current neutralizes B's working current so that the compensation currents in both receiving instruments hold the armatures attracted for the two dashes. Meanwhile A's dash ends and he releases his key. At once his line current ceases to neutralize B's line current, his receiving instrument is actuated now by B's line current, while B's receiving instrument ceases to be actuated by the compensation current.

Two assumptions are made in the above description. The line currents are assumed to be equal in strength and opposite in direction at each station. Neither of these is necessary. The line current received at a station is always weaker than the outgoing line current, and it is the preponderance of the compensation current over the partly neutralized line current that does the work. As this preponderance is very nearly equal to the line current received from the distant station, the signals are actuated by almost the same current, whether it is compensation or line current.


Both line currents may coincide in direction. Then when the two keys are depressed, a line current of double strength goes through both receiving instruments and both work by preponderance of the double line current over the compensation current. In other respects the operation is the same as before described.



The cut shows a diagram of the operation of one end of the line. R and R are resistances, E and E are earth contacts, and the two circles show the magnet of the receiving instrument wound with two coils in opposition. The battery and key are also shown. It also illustrates what happens if the key of the receiver is in the intermediate position breaking contact at both 1 and 2. The sender's line current then goes through both coils of the receiving instrument magnet, but this time in series, and in coincident direction. This actuates the instrument as before. Owing to the resistance only half the normal current passes, but this half goes through twice as many coils or turns as if the receiver's key was in either of the other two positions.

In actual practice there are many refinements. To compensate for the varying resistance of the line a rheostat or resistance with sliding connection arm is connected in the compensation circuit so that the resistance can be instantly changed. As the electro-static capacity of the line varies sectional condensers are also connected in the compensation circuits.


Telegraph, Facsimile. A telegraph for transmitting facsimiles of drawing or writing. The methods employed involve the synchronous rotation of two metallic cylinders, one at the transmitting end, the other at the receiving end.

On the transmitter the design is drawn with non-conducting ink. A tracer presses upon the surface of each cylinder and a circuit is completed through the two contacts. In operation a sheet of chemically prepared paper is placed over the surface of the receiving cylinder. The two cylinders are rotated in exact synchronism and the tracers are traversed longitudinally as the cylinders rotate. Thus a number of makes and breaks are produced by the transmitting cylinder, and on the receiving cylinder the chemicals in the paper are decomposed, producing marks on the paper exactly corresponding to those on the transmitting cylinder.

Synonyms—Autographic Telegraph—Pantelegraphy.

Telegraph, Harmonic Multiplex. A telegraph utilizing sympathetic vibration for the transmission of several messages at once over the same line. It is the invention of Elisha Gray. The transmitting instrument comprises a series of vibrating reeds or tuning-forks, each one of a different note, kept in vibration each by its own electro-magnet. Each fork is in its own circuit, and all unite with the main line so as to send over it a make and break current containing as many notes superimposed as there are tuning forks. At the other end of the line there are corresponding tuning forks, each with its own magnet. Each fork at this end picks up its own note from the makes and breaks on the main line, by the principle of sympathetic vibration.

To each pair of operators a pair of forks of identical notes are assigned. As many messages can be transmitted simultaneously as there are pairs of forks or reeds.

The movements of a telegraph key in circuit with one of the transmitting reeds sends signals of the Morse alphabet, which are picked out by the tuning fork of identical note at the other end of the line.


Telegraph, Hughes'. A printing telegraph in very extensive use in continental Europe. Its general features are as follows:

The instruments at each end of the line are identical. Each includes a keyboard like a piano manual, with a key for each letter or character. On each machine is a type wheel, which has the characters engraved in relief upon its face. With the wheel a "chariot" as it is termed also rotates. The type wheels at both stations are synchronized. When a key is depressed, a pin is thrown up which arrests the chariot, and sends a current to the distant station. This current causes a riband of paper to be pressed up against the face of both type wheels so as to receive the imprint of the character corresponding to the key. The faces of the wheels are inked by an inking roller.


The most characteristic feature is the fact that the current sent by depressing a key does not attract an armature, but releases one, which is then pulled back by a spring. The armature is restored to its position by the mechanical operation of the instrument. The magnet used is a polarized electro-magnet. Coils are carried on the ends of a strong powerful magnet. The coils are so connected that a current sent through them by depressing a key is in opposition to the magnetism of the permanent magnet so that it tends to release the armature, and in practice does so. This release permits the printing mechanism to act. The latter is driven by a descending weight, so that very slight electric currents can actuate the instruments.

Synonym—Hughes' Type Printer.

Telegraphic Code. (a) The telegraphic alphabet, as of the Morse System. (See Alphabet, Telegraphic.)

(b) A code for use in transmitting messages either secretly, or comprising several words or short sentences in one word, in order to economize in transmission. Such codes are extensively used in commercial cable messages.


Telegraph, Magneto-electric. A telegraph in which the current is produced by magneto-electric generators. It has been applied to a considerable extent in England. The Wheatstone ABC or dial telegraph is operated by a magneto-generator turned by hand.

In this country the magneto-electric generator by which the calling bell of a telephone is rung is an example. The magneto-electric key (See Key, Magneto-electric) is for use in one kind of magneto-electric telegraphing.

Telegraph, Morse. A telegraph, characterized by the use of a relay, working a local circuit, which circuit contains a sounder, or recorder for giving dot and dash signals constituting the Morse alphabet. The signals are sent by a telegraph key, which when depressed closes the circuit, and when released opens it. The two underlying conceptions of the Morse Telegraph system are the use of the dot and dash alphabet, and the use of the local circuit, which circuit includes a receiving instrument, and is worked by a relay, actuating a local battery. It would be difficult to indicate any invention in telegraphy which has had such far-reaching consequences as the one known as the Morse telegraph.

In other places the principal apparatus of the system will be found described. The cut Fig. 318, repeated here gives the general disposition of a Morse system. (See Circuit, Local.)



The key by which the messages are transmitted is shown in Fig. 319. M is a base plate of brass. A is a brass lever, mounted on an arbor G carried between adjustable set screws D. C is the anvil where contact is made by depressing the key by the finger piece B of ebonite. E, Fl are adjusting screws for regulating the vertical play of the lever. H is the switch for opening or closing the circuit. It is opened for transmission, and closed for receiving. By screws, L L, with wing nuts, K K, the whole is screwed down to a table.


In the United States the simplest disposition of apparatus is generally used. The main line is kept on closed circuit. In it may be included a large number of relays at stations all along the line, each with its own local circuit. There may be fifty of such stations. Battery is generally placed at each end of the line. Very generally gravity batteries are used, although dynamos now tend to supplant them in important stations.

As relays the ordinary relay is used. Its local circuit includes a sounder and local battery. The latter is very generally of the gravity type, but oxide of copper batteries (See Battery, Oxide of Copper) are now being introduced. At main or central offices, the terminals of the lines reach switch boards, where by spring-jacks and plugs, any desired circuits can be looped into the main circuit in series therewith.

In European practise the main line is kept on open circuit. Polarized relays are used to work the local circuits. The currents for these have to be alternating in direction. When the line is not in use its ends are connected to earth at both ends, leaving the battery out of circuit. Each intermediate station has its own main, or line battery for use when it desires to send a message. In the American system as first described, it will be seen that the main batteries are at most two in number.

For the details of the different apparatus, the following definitions may be consulted: Embosser, Telegraphic—Recorder, Morse—Relay—Relay Connection—Sounder.


Telegraph, Multiplex. A system of telegraphy by which a number of messages can be transmitted in both directions over a single wire. The principles underlying the systems are the following:

Suppose that at the two extremities of a telegraph line two arms are kept in absolute synchronous rotation. Let the arms in their rotation, press upon as many conducting segments as there are to be transmissions over the line. A transmitting and receiving set of instruments may be connected to one segment at one end of the line, and another set to the corresponding segment at the distant station. For each pair of segments two sets can be thus connected. Then if the arm rotates so rapidly that the contacts succeed each other rapidly enough each pair of sets of instruments can be worked independently of the others. In practice this rapid succession is effected by having a number of contacts made for each pair during a single rotation of the arm or equivalent.

The multiplex system has been perfected by the use of La Cour's phonic wheel (see Phonic Wheel), and brought into a practical success by Patrick B. Delany, of New York.

Two phonic wheels rotate at each end of the line. They are kept in synchronous motion by two vibrating steel reeds of exactly the same fundamental note, and the axle of each wheel carries an arm whose end trails over the contacts or distributor segments already spoken of. The reeds are adjusted to vibrate at such speed that the trailer is in contact with each segment about 1/500 second. The number of groups of segments required for each working is determined by the retardation of the signals owing to the static capacity of the line. To convert the rapidly recurring impulses of current into practically a single current, condensers are connected across the coils of the relay. One battery serves for all the arms.

Multiplex telegraphy can effect from two to six simultaneous transmissions over one wire. For two or four transmissions the method only distinguishes it from duplex or quadruplex telegraphy. The terms diode, triode, tetrode, pentode and hexode working are used to indicate respectively the simultaneous transmission of two, three, four, five, or six messages over one wire.

It will be seen that the multiplex process really assigns to each transmission separate times, but divides these times into such short and quickly recurring intervals that the work is executed as if there was continuous contact. In no case is there the popular conception of the sending of several messages actually simultaneously over one wire. Each signal in reality has its own time assigned it, divided into short periods of high frequency, and only utilizes the line when it is free.


Telegraph, Over-house. An English term for telegraph lines led over houses and supported on standards on the roofs.

Telegraph Pole Brackets. Arms for carrying insulators, which arms are attached to telegraph poles or other support. They vary in style; sometimes they are straight bars of wood gained into and bolted or spiked in place; sometimes they are of iron.

Telegraph, Printing. Various telegraphs have been invented for printing in the ordinary alphabet the messages at the receiving end of the line.

Representative instruments of this class are used for transmitting different market and stock reports to business offices from the exchanges. The type faces are carried on the periphery of a printing wheel, which is rotated like the hand of a dial telegraph, and against whose face a paper riband is pressed whenever the proper letter comes opposite to it. As each letter is printed the paper moves forward the space of one letter. Spacing between words is also provided for. In the recent instruments two lines of letters are printed on the paper one above the other.

In England, and on the continent of Europe, printing instruments have received considerable use for ordinary telegraphic work. Hughes' type printer and Wheatstone's ABC telegraph meet with extensive use there for ordinary transmission.

Telegraph, Quadruplex. Duplex telegraphy is the sending of two messages in opposite directions simultaneously through the same wire. Duplex telegraphy is the sending of two messages simultaneously in the same direction. The two combined constitute quadruplex telegraphy. [SIC]

The system was suggested by Stark of Vienna and Bosscha of Leyden in 1855; the successful problem was solved by Edison in 1874.

The principle is based on the two orders of difference in electric currents; they may vary in strength or in direction. Thus we may have one instrument which works with change of strength of current only, the other with change of direction only. The two can be worked together if the direction of the current can be altered without alteration of strength, and if strength can be altered without alteration of direction. Double current and single current working are so combined that one relay works by one system of currents and another relay by the other system. A current is constantly maintained through the line. The relay operated by change in direction is a simple polarized relay which works by change of direction of current. The relay operated by change in strength is the ordinary unpolarized relay.


For the following description and the cuts illustrating it we are indebted to Preece and Sivewright. The cut shows the arrangement of the apparatus and connections for terminal offices.

"Sufficient table room is provided to seat four clerks. The apparatus is arranged for the two senders to sit together in the centre, the messages to be forwarded being placed between them. The section on the left of the switch Q is known as the 'A' side, that on the right as the 'B' side of the apparatus.

K1 the reversing key, reverses the direction of the current. K2 is a simple key, known as the increment key; it is used simply to increase the strength of the current.


The way in which the keys K1 and K2 combine their action is shown by Fig. 321. E1 and E2 are the line batteries, the one having two and one-third (2-1/3) the number of cells of the other, so that if E1 be the electro-motive force of the smaller, that of the whole combined battery will be 3.3 E1. The negative pole of E1 is connected to z and z1 of K1 and the positive pole of E2 to a of K2 through a resistance coil s. A wire, called the 'tap' wire, connects the positive pole of E1 and the negative pole of E2 to b of K2. This wire has in it a resistance coil r2. The springs c and c1 of Kl are connected to the lever L of K2. Now, when both keys are at rest, the negative pole of E1 is to line through z, and the positive pole of E1 to earth through b of K2 and c of K1; the positive pole of E2 being insulated at a of K2.


There is thus a weak negative current flowing to line. When K1 alone is worked, the current of E1 is reversed. When K2 is worked alone, c of K1 is transferred from b to a, and the strength of the negative current going to line is increased through the increase of the electro-motive force from E1 to 3.3 E1 for the whole battery is brought into play. When K1 and K2 are depressed together, then the negative pole of E1 goes to earth through Z1; and the positive pole of E2 to line through a of K2 and c1 of K1 and a positive current, due to the whole electro-motive force 3.3 E1 goes to line. Hence the effect of working K1 is simply to reverse the current, whatever its strength, while that of K2 is to strengthen it, whatever its direction.

The resistance coil s, of 100 resistance, is called a spark coil, because it prevents the high electro-motive force of the whole battery from damaging the points of contact by sparking or forming an arc across when signals are sent; and the resistance r2 is made approximately equal to the combined resistance of E2 and the spark coil, so that the total resistance of the circuit may not be altered by the working of the apparatus.


A1 and B1 (Fig. 320) are the relays which are used to respond to the changes in the currents sent by the keys K1 and K2 at the distant station.

A, is a simple polarized relay wound differentially, each wire having a resistance of 200 [omega], and so connected up as to respond to the working of the reversing key K1 of the distant station. It acts independently of the strength of the current, and is therefore not affected by the working of the increment key K2. It is connected up so as to complete the local circuit of the sounder S1 and the local battery l1 and forms the receiving portion of the 'A' side.

B, is a non-polarized relay also wound differentially, each coil having a resistance of 200 [omega]. It responds only to an increase in the strength of the current, and therefore only to the working of the increment key K2 of the distant station.

[Transcriber's note: In current usage upper case omega indicates ohms and lower case omega denotes angular frequency, 2*PI*f.]


The relay spring is so adjusted that the armatures are not actuated by the weak current sent from E by the key K1.

In its normal position this relay completes the circuit of the local battery through the sounder S. This sounder S, called the uprighting sounder, acts as a relay to a second sounder, S2, called the reading sounder, which is worked by another local battery, l2. Of course, normally, the armature of S is held down and that of S2 is up, but when the tongue t moves, as it does when the increment key K2 is depressed so as to send the whole current to line, then the current from l is interrupted, and the circuit of l2 is completed by the rising of the armature of S, causing the reading sounder S2 to work. This is the 'B' side.

R is a rheostat for balancing the resistance of the line, as used in duplex working.

C is a condenser used for compensating the static charge of the line. It is provided with an adjustable retardation coil, R1, to prolong the effect of the compensating current from the condenser.

G is a differential galvanometer, used for testing, and for facilitating adjustment and balancing.

Q is a switch for putting the line to earth, either for balancing, or for any other purpose. There is on the earth wire leading from Q a resistance coil, r1, equalling approximately the resistance of the whole battery, 3.3 E1, and the resistance s.

The connections shown in Fig. 321, are for an 'up' office. At a 'down' office it is necessary to reverse the wires on the two lower terminals of the galvanometer and the two battery wires on the reversing key K1.

The keys K1 and K2 are, for repeaters, replaced by transmitters.

The adjustment of this apparatus requires great care and great accuracy. Its good working depends essentially on technical skill that can only be acquired by patience and perseverance.

Faults in working generally arise from careless adjustments, dirty contacts, loose connections, battery failures, and the ordinary line interruptions, but there are no troubles that are beyond the reach of ordinary skill, and it can be safely said that, within moderate distances, wherever and whenever duplex working is practicable, then quadruplex working is so too."

The above is a typical quadruplex bridge system. There is also a differential system, the full description of which, in addition to what has been given, is outside of the scope of this work.


Telegraph Repeater. An extension of the relay system, adopted for long lines. A repeating station comprises in general terms duplicate repeating apparatus. One set is connected for messages in one direction, the other for messages in the opposite direction. The general operation of a repeating set is as follows. The signals as received actuate a relay which by its local circuit actuates a key, which in ordinary practise would be the sounder, but in the repeater its lever opens and closes a circuit comprising a battery and a further section of the line.

Repeaters are placed at intervals along the line. Each repeater repeats the signals received for the next section of line with a new battery. It represents an operator who would receive and repeat the message, except that it works automatically.

The Indo-European line from London to Teheran, 3,800 miles long, is worked directly without any hand retransmission, it being carried out by five repeaters. This gives an average of over 500 miles for each repeater. [Transcriber's note: 650 miles for each repeater.]

Repeaters introduce retardation, and each repeater involves a reduction in the rate of working. Yet in many cases they increase the speed of a line greatly, as its speed is about equal to that of its worst section, which may be far greater than that of the whole line in one.


Telegraph Signal. In the telegraph alphabet, a dot, or dash; the signal or effect produced by one closing of the circuit. A dash is equal in length to three dots. The space between signals is equal to one dot; the space between letters to three dots; and the space between words to six dots.

Telegraph, Single Needle. A telegraph system in which the code is transmitted by the movements of a needle shaped index which oscillates to right and left, the left hand deflection corresponding to dots, the right hand deflection to dashes. The instruments for sending and receiving are combined into one. The needles are virtually the indexes of vertical galvanometers. In one form by a tapper key (see Tapper), in another form by a key worked by a drop-handle (the drop handle instrument), currents of opposite directions are sent down the line. These pass through both instruments, affecting both needles and causing them to swing to right or left, as the operator moves his key.

As galvanometer needle or actuating needle a soft iron needle is employed, which is polarized by the proximity of two permanent magnets. This avoids danger of reversal of polarity from lightning, a trouble incident to the old system.


The cut, Fig. 322, shows a single needle telegraph instrument of the tapper form. The action of the tapper can be understood from the next cut.



C and Z are two strips of metal to which the positive and negative poles of the battery are respectively connected. E and L are two metallic springs; E is connected to earth, L is connected to the line; at rest both press against Z. If L is depressed so as to touch C, the current from the battery goes to the line by the key L, goes through the coils of the distant instrument and deflects the needle to one side, and then goes to the earth. If the key E is depressed, L retaining its normal position, the direction of the current is reversed, for the other pole of the battery is connected to the earth and the reverse current going through the coils of the distant instrument deflects the galvanometer needle to the other side.

In the drop-handle type an analogous form of commutator worked by a single handle produces the same effects.


Telegraph, Wheatstone, A. B. C. A magneto-electric telegraph of the dial system. An alternating current magneto-generator is turned by hand and by depressing keys its current is admitted to or cut off from the line and receiver's instrument. The message is received by a dial instrument working by the escapement motion described under Telegraph, Dial.

Telegraph, Writing. A telegraph in which the message is received in written characters. The transmitter includes a stylus which is held in the hand and whose point bears against the upper end of a vertical rod. The rod is susceptible of oscillation in all directions, having at its base a spring support equivalent to a universal joint.

The stylus is moved about in the shape of letters. As it does this it throws a series of resistances in and out of the circuit.

At the receiving end of the line the instrument for recording the message includes two electro-magnets with their cores at right angles to each other and their faces near together at the point of the angle. An armature is supported between the faces and through it a vertical rod carried by a spring at its bottom rises. These magnets receive current proportional to the resistances cut in and out by the motions of the other rod at the transmitting end of the line. These resistances are arranged in two series at right angles to each other, one for each magnet. Thus the movements of the transmitting stylus and rod are repeated by the end of the rod in the receiving instrument. A species of pen is carried at the end of the rod of the receiving instrument, which marks the letters upon a riband of paper which is fed beneath it.

Telemanometer. Electric. A pressure gauge with electric attachment for indicating or recording its indications at a distance.

It is applicable to steam boilers, so as to give the steam pressure in any desired place.

Telemeter, Electric. An apparatus for electrically indicating or recording at a distance the indications of any instrument such as a pressure gauge, barometer or thermometer, or for similar work. The telemanometer applied to a boiler comes into this class of instrument.

Telephotography. The transmission of pictures by the electric current, the requisite changes in the current being effected by the action of light upon selenium. The picture is projected by a magic lantern. Its projection is traversed by a selenium resistance through which the current passes. This is moved systematically over its entire area, thus constituting the transmitter, and synchronously with the motion of the selenium a contact point at the other end of the line moves systematically over a sheet of chemically prepared paper. The paper, which may be saturated with a solution of potassium ferrocyanide and ammonium nitrate, is stained by the passage of the current, and by the variation in intensity of staining, which variation is due to variations in the current, produced by the effects of the light upon the selenium, the picture is reproduced.


Telepherage. An electric transportation system, hitherto only used for the carrying of ore, freight, etc. Its characteristic feature is that the electric conductors, suspended from poles, supply the way on which carriages provided with electric motors run. The motors take their current directly from the conductors.

There are two conducting lines, running parallel with each other, supported at the opposite ends of transverse brackets on a row of supporting poles. At each pole the lines cross over so that right line alternates with left, between consecutive pairs of poles.

The cars are suspended from pulleys running on one or the other of the conductors. A train of such cars are connected and the current is taken in near one end and leaves near the other end of the train. These current connections are so distant, their distance being regulated by the length of the train, that they are, for all but an instant at the time of passing each of the poles, in connection with segments of the line which are of opposite potential. To carry out this principle the distance between contacts is equal to the distance between poles. Owing to the crossing over of the lines the contacts are in connection as described and thereby the actuating current is caused to go through the motors.

Cars running in one direction go on the electric conductors on the one side, those running in the other direction go on the other conductor.

A great many refinements have been introduced, but the system has been very little used.

Telephone. An instrument for the transmission of articulate speech by the electric current. The current is defined as of the undulatory type. (See Current, Undulatory.)

The cut shows what may be termed the fundamental telephone circuit. A line wire is shown terminating in ground plates and with a telephone in circuit at each end. The latter consists of a magnet N S with a coil of insulated wire H surrounding one end. Facing the pole of the magnet is a soft iron diaphragm D, held in a frame or mouthpiece T. Any change of current in the line affects the magnetism of the magnet, causing it to attract the diaphragm more or less. The magnet and diaphragm really constitute a little electric motor, the diaphragm vibrating back and forth through an exceedingly short range, for changes in the magnetic attraction.

The principle of the reversibility of the dynamo applies here. If the magnet is subjected to no change in magnetism, and if the diaphragm is moved or vibrated in front of its poles, currents will be induced in the wire bobbin which surrounds its end. If two such magnets with bobbins and diaphragms are arranged as shown, vibrations imparted to one diaphragm will send currents through the line which, affecting the magnetism of the distant magnet, will cause its diaphragm to vibrate in exact accordance with the motions of the first or motor diaphragm. In the combination one telephone represents a dynamo, the other a motor.

If the vibrations of the diaphragm are imparted by the voice, the voice with all its modulations will be reproduced by the telephone at the distant end of the line.




The above gives the essential features of the Bell telephone. In practice the telephone is used only as the receiver. As transmitter a microphone is employed. To give the current a battery, generally of the open circuit type, is used, and the current in the line is an induced or secondary one.

The microphone which is talked to, and which is the seat of the current variations which reproduce original sound, is termed the transmitter, the telephone in which the sounds are produced at the distant end of the line is termed the receiver.

Fig. 325 shows the construction of the Bell telephone in universal use in this country as the receiver. M is a bar magnet, in a case L L. B B is a bobbin or coil of insulated wire surrounding one end of the magnet. D is the diaphragm of soft iron plate (ferrotype metal), and E is the mouthpiece. The terminals of the coil B B connect with the binding screws C C. The wire in the coil is No. 36, A. W. G., and is wound to a resistance of about 80 ohms.


As typical transmitter the Blake instrument may be cited. It is a carbon microphone. It is shown in section in the cut; a is the mouthpiece and e is a diaphragm of iron plate, although other substances could be used; f is a steel spring, with a platinum contact piece at its end. One end bears against the diaphragm, the other against a carbon block k. The latter is carried by a brass block p, and pressure is maintained between these contacts by the spring g and weight of the piece c, which by gravity tends to press all together. The current passes by way of the spring f, carbon button k and spring g through the circuit indicated.

A battery is in circuit with these parts. If a telephone is also in circuit, and the transmitter is spoken against, the diaphragm vibrating affects the resistance of the carbon-platinum contact, without even breaking the contact, and the telephone reproduces the sound. The heavy piece of metal C acts by its inertia to prevent breaking of the contact. The position of this piece c, which is carried by the brass plate m, is adjusted by the screw n.


In practice the transmitter and battery are usually on a local circuit, which includes the primary of an induction coil. The line and distant receiving telephone are in circuit with the secondary of the induction coil, without any battery.

Telephone, Bi-. A pair of telephones carried at the ends of a curved bar or spring so that they fit the head of a person using them. One telephone is held against each ear without the use of the hands.


Telephone, Capillary. A telephone utilizing electro-capillarity for the production of telephonic effects. The following describes the invention of Antoine Breguet.

The point of a glass tube, drawn out at its lower end to a capillary opening dips vertically into a vessel. This vessel is partly filled with mercury, over which is a layer of dilute sulphuric acid. The end of the immersed tube dips into the acid, but does not reach the mercury. One line contact is with mercury in the tube, the other with the mercury in the vessel. The arrangement of tube and vessel is duplicated, giving one set for each end of the line. On introducing a battery in the circuit the level of the mercury is affected by electro-capillarity. The tubes are closed by plates or diaphragms at their tops, so as to enclose a column of air. It is evident that the pressure of this air will depend upon the level of the mercury in the tube, and this depends on the electro-motive force. On speaking against the diaphragm the sound waves affect the air pressure, and consequently the level, enough to cause potential differences which reproduce the sound in the other instrument.


Telephone, Carbon. A telephone transmitter based on the use of carbon as a material whose resistance is varied by the degree of pressure brought to bear upon it. Undoubtedly the surface contact between the carbon and the other conducting material has much to do with the action. Many carbon telephones have been invented. Under Telephone the Blake transmitter is described, which is a carbon telephone transmitter. The Edison carbon transmitter is shown in section in the cut. E is the mouth piece and D the diaphragm. I is a carbon disc with adjusting screw V. A platinum plate B B, with ivory button b, is attached to the upper surface of the carbon disc. C C is an insulating ring. The wire connections shown bring the disc into circuit. It is connected like a Blake transmitter. It is now but little used.



Telephone, Chemical. A telephone utilizing chemical or electrolytic action in transmitting or receiving. The electro-motograph is an example of a chemical receiver. (See Electro-motograph.)

Telephone, Electrostatic. A telephone utilizing electrostatic disturbances for reproduction of the voice. In the cut D and C are highly charged electrophori. The diaphragms A and B when spoken to affect the potential of the electrophorus so as to produce current variations which will reproduce the sound. Dolbear and others have invented other forms of transmitters based on electrostatic action. Receivers have also been constructed. A simple condenser may be made to reproduce sound by being connected with a powerful telephone current.


Telephone Induction Coil. The induction coil used in telephone circuits for inducing current on the main line. It is simply a small coil wound with two separate circuits of insulated wire. In the Edison telephone the primary coil, in circuit with the transmitter, is of No. 18 to 24 wire and of 3 to 4 ohms resistance. The secondary in circuit with the line and receiving instrument is of No. 36 wire and of 250 ohms resistance. The Bell telephone induction coil has its primary of No. 18 to 24 wire wound to a resistance of 1/2 ohm, and its secondary of No. 36 wire, and of 80 ohms resistance.


Telephone, Reaction. A form of telephone containing two coils of insulated wire, one of which is mounted on the disc, and the other on the magnet pole in the usual way. These coils react upon each other so as to strengthen the effect.

Telephone, Thermo-electric. A telephone transmitter including a thermo-electric battery, placed in circuit with the line. A plate of vulcanite faces it. When the sound waves strike the vulcanite they move it backward and forward. These movements, owing to the elasticity of the vulcanite, produce minute changes of temperature in it, which affecting the thermo-electric pile produce in the circuit currents, which passing through a Bell telephone cause it to speak. This type of instrument has never been adopted in practice.

Telephote. An apparatus for transmitting pictures electrically, the properties of selenium being utilized for the purpose.


Teleseme. An annunciator, displaying on a dial the object wanted by the person using it. It is employed to transmit messages from rooms in a hotel to the office, or for similar functions.

Tele-thermometer. A thermometer with electric attachment for indicating or recording its indications at a distance.

Tempering, Electric. A process of tempering metals by electrically produced heat. The article is made part of an electric circuit. The current passing through it heats it, thereby tempering it. For wire the process can be made continuous. The wire is fed from one roll to another, and if required one roll may be immersed in a liquid bath or the wire between the rolls may be led therein. The current is brought to one roll and goes through the wire to the other. As it does this the wire is constantly fed from one roll to another. The bath may be used as described to cool it after the heating. The amount of heating may be regulated by the rate of motion of the wire.


Ten, Powers of. This adjunct to calculations has become almost indispensable in working with units of the C. G. S. system. It consists in using some power of 10 as a multiplier which may be called the factor. The number multiplied may be called the characteristic. The following are the general principles.

The power of 10 is shown by an exponent which indicates the number of ciphers in the multiplier. Thus 10^2 indicates 100; 10^3 indicates 1,000 and so on.

The exponent, if positive, denotes an integral number, as shown in the preceding paragraph. The exponent, if negative, denotes the reciprocal of the indicated power of 10. Thus 10^-2 indicates 1/100; 10^-3 indicates 1/1000 and so on.

The compound numbers based on these are reduced by multiplication or division to simple expressions. Thus: 3.14 X 10^7 = 3.14 X 10,000,000 = 31,400,000. 3.14 X 10^-7 = 3.14/10,000,000 or 314/1000000000. Regard must be paid to the decimal point as is done here.

To add two or more expressions in this notation if the exponents of the factors are alike in all respects, add the characteristics and preserve the same factor. Thus:

(51X 10^6) + (54 X 10^6) = 105 X 10^6. (9.1 X 10^-9) + (8.7 X 10^-9) = 17.8 X 10^-9.

To subtract one such expression from another, subtract the characteristics and preserve the same factor. Thus:

(54 X 10^6) - (51 X 10^6) = 3 X 10^6.

If the factors have different exponents of the same sign the factor or factors of larger exponent must be reduced to the smaller exponent, by factoring. The characteristic of the expression thus treated is multiplied by the odd factor. This gives a new expression whose characteristic is added to the other, and the factor of smaller exponent is preserved for both,

Thus: (5 X 10^7) + (5 X10^9) = (5 X 10^7) + (5 X 100 X 10^7) = 505 X 10^7.

The same applies to subtraction. Thus: (5 X 10^9) - (5 X 10^7) = (5 X 100 X 10^7) - (5 X 10^7) = 495 X 10^7.

If the factors differ in sign, it is generally best to leave the addition or subtraction to be simply expressed. However, by following the above rule, it can be done. Thus:

Add 5 X 10^-2 and 5 X 10^3. 5 X 10^3 = 5 X 10^5 X 10^-2 (5 X 10^5 X 10^-2) + (5 X 10^-2) = 500005 X 10^-2

This may be reduced to a fraction 500000/100 = 5000.05.

To multiply add the exponents of the factors, for the new factor, and multiply the characteristics for a new characteristic. The exponents must be added algebraically; that is, if of different signs the numerically smaller one is subtracted from the other one, and its sign is given the new exponent.

Thus; (25 X 10^6) X (9 X 10^8) = 225 X 10^14. (29 X 10^ -8) X (11 X 10^7) = 319 X 10^-1 (9 X 10^8) X (98 X 10^2) = 882 X 10^1


To divide, subtract (algebraically) the exponent of the divisor from that of the dividend for the exponent of the new factor, and divide the characteristics one by the other for the new characteristic. Algebraic subtraction is effected by changing the sign of the subtrahend, subtracting the numerically smaller number from the larger, and giving the result the sign of the larger number. (Thus to subtract 7 from 5 proceed thus; 5 - 7 = -2.)

Thus; (25 X 10^6) / (5 X 10^8) = 5 X 10^-2 (28 X 10^-8) / (5 X 10^3) = 5.6 X 10^-11

[Transcriber's note: I have replaced ordinary exponential notation by the more compact and simpler "programming" representation. The last two example would be: 25E6 / 5E8 = 5E-2 28E-8 / 5E3 = 5.6E-11 ]

Tension. Electro-motive force or potential difference in a current system is often thus termed. It is to be distinguished from intensity or current strength, which word it too greatly resembles.

Tension, Electric. (a) The condition an electrified body is brought into by electrification, when each molecule repels its neighbor. The condition is described as one of self-repulsion.

(b) The voltage or potential difference of a circuit is also thus termed.

Terminal. The end of any open electric circuit, or of any electric apparatus; as the terminals of a circuit, dynamo, or battery.

Terminal Pole. In telegraph line construction the last pole of a series; one beyond which the line is not carried. Such pole, as the pull of the wires is all in one direction, requires special staying or support. The regular line poles are free from this strain, as the wire pulls in both directions.

Tetanus, Acoustic. A term in electro-therapeutics. An effect produced on a nerve by very rapidly alternating induced currents. The currents are produced by an induction coil with a vibrator giving a musical note. This is a species of gauge of proper frequency of alternations.

Theatrophone. An apparatus worked by automatic paying machinery by which a telephone connection is made with a theatre or opera by the deposition of a coin in a slot.

Therm. A unit of heat. It has been proposed by the British Association and amounts to a redefinition of the smaller calorie. It is the amount of heat required to raise the temperature of one gram of water one degree centigrade, starting at the temperature of maximum density of water.


Thermaesthesiometer. An electro-therapeutic instrument for testing the sensitiveness of the surface of the body to changes of temperature. Vessels of mercury are provided with thermometers to indicate their temperature. One vessel is surrounded by an electric conductor wound in a number of turns. The temperature is raised by passing a current through this. By successive applications of the vessels to the same spot upon the skin the power of differentiating temperatures is determined.

Thermo Call. (a) An electric alarm or call bell operated by thermo-electric currents. It may serve as a fire alarm or heat indicator, always bearing in mind the fact that differential heat is the requisite in a thermo-electric couple.

(b) See Thermo-electric Call.

Thermo-chemical Battery. A voltaic battery in which the electro-motive force is generated by chemical action induced by heat.

The chemical used generally is sodium nitrate or potassium nitrate. The positive plate is carbon. On heating the battery the nitrate attacks the carbon, burning it and produces potential difference. For negative plate some metal unattacked by the nitrate may be employed.


Thermo-electric Battery or Pile. A number of thermo-electric couples q. v., connected generally in series.

In Nobili's pile the metals are bismuth and antimony; paper bands covered with varnish are used to insulate where required. In Becquerel's pile copper sulphide (artificial) and German silver, (90 copper, 10 nickel) are the two elements. The artificial copper sulphide is made into slabs 4 inches long, 3/4 inch wide, and 1/2 inch thick (about). Water is used to keep one set of junctions cool, and gas flames to heat the other set. In Fig. 331, c, d represent the binding screws. The couples are mounted on a vertical standard, with adjusting socket and screw B, so that its lower end can be immersed in cold water, or raised therefrom as desired.



Fig. 332 shows one couple of the battery. S is artificial antimony sulphide; M is German silver; m is a protecting plate of German silver to save the sulphide from wasting in the flame.


Clamond's pile has been used in practical work. The negative element is an alloy of antimony, 2 parts, zinc, 1 part. The positive element is tin plate. Mica in some parts, and a paste of soluble glass and asbestus in other parts are used as insulators. They are built up so as to form a cylinder within which the fire is maintained. The air is relied on to keep the outer junctions cool. The temperature does not exceed 200 C. (392 F.)

Sixty such elements have an electro-motive force of 300 volts and an internal resistance of 1.5 ohms. Such a battery requires the consumption of three cubic feet of gas per hour. (See Currents, Thermo-electric. )


Thermo-electric Call. A thermostat arranged to ring a bell or to give some indication when the temperature rises or falls beyond certain points. It may be a compound bar of brass and steel fixed at one end and free for the rest of its length. Its end comes between two adjustable contacts. As the temperature rises it bends one way (away from the brass side) and, if hot enough, touching a contact gives one signal. If the temperature falls it curves the other way, and if cold enough touches the other contact, giving another signal. (See Thermostat, Electric.)

Thermo-electric Couple. If two dissimilar conductors form adjacent parts of a closed circuit, and their junction is at a different temperature than that of the rest of the circuit, a current will result. Such pair of conductors are called a thermo-electric couple. They may be joined in series so as to produce considerable electro-motive force. (See Thermo-electricity and other titles in thermo-electricity.)

The efficiency of a thermo-electric couple according to the second law of thermo-dynamics is necessarily low—not over 10 per cent.

Thermo-electric Diagram. A diagram indicating the change in potential difference for a fixed difference of temperature between different metals at different temperatures. It is laid out with rectangular co-ordinates. On one axis temperatures are laid off, generally on the axis of abscissas. On the other axis potential differences are marked. Different lines are then drawn, one for each metal, which show the potential difference, say for one degree centigrade difference of temperature between their junctions, produced at the different temperatures marked on the axis of abscissas.


Thus taking copper and iron we find at the temperature 0 C. (32 F.) a difference of one degree C. (1.8 F.) in their junctions will produce a potential difference of 15.98 micro volts, while at 274.5 C. (526.1 F.) the lines cross, and zero difference of potential is indicated. Taking the lead line on the same diagram it crosses the iron line a little above 350 C. (662 F.), indicating that if one junction is heated slightly above and the other is heated slightly below this temperature no potential difference will be produced. Lead and copper lines, on the other hand, diverge more and more as the temperature rises.


Thermo-electric Inversion. The thermo-electric relations of two conductors vary at different temperatures. Sometimes at a definite point they have no electro-motive force and after passing this point the positive plate becomes a negative one and vice versa. This is inversion, or reversal. (See Thermo-electric Diagram.)

Synonym— Thermo-electric Reversal.

Thermo-electricity. Electric energy, electro-motive force or electrification produced from heat energy by direct conversion. It is generally produced in a circuit composed of two electric conductors of unlike material, which circuit must possess at least two junctions of the unlike substances. By heating one of these to a higher temperature than that of the other, or by maintaining one junction at a different temperature from that of the other a potential difference is created accompanied by an electric current.

In many cases differential application of heat to an identical material will develop potential difference. This effect, the converse of the Thomson effect, is not used to produce currents, as in a closed circuit the potential differences due to differential heating would neutralize each other.

Thermo-electric Junction. A junction between two dissimilar conductors, which when heated or cooled so as to establish a differential temperature, as referred to the temperature of the other junction, produces potential difference and an electric current.

Thermo-electric Pile, Differential. A thermo-electric pile arranged to have opposite faces subjected to different sources of heat to determine the identity or difference of temperature of the two sources of heat. It corresponds in use to a differential air thermometer.

Thermo-electric Power. The coefficient which, multiplying the difference of temperature of the ends of a thermo-electric couple, gives the potential difference, expressed in micro-volts. It has always to be assigned to a mean or average temperature of the junctions, because the potential difference due to a fixed difference of temperature between two metals varies with the average temperature of the two junctions. (See Thermo-electric Diagram.)

For bismuth and antimony at 19.5 C. (67.1 F.) it is 103 microvolts per degree Centigrade (1.8 F.). This means that if one junction is heated to 19 C. and the other to 20 C. (66.2 F. and 68.0 F.) a potential difference of 103 micro-volts will be produced.

The potential difference is approximately proportional to the difference of temperature of the two junctions if such difference is small. Hence for large differences of potential the thermo-electric power coefficient does not apply.

As a differential function it is thus deduced by Sir William Thomson, for expressing the E. M. F. in a thermo-electric circuit: If a circuit is formed of two metals with the junctions at indefinitely near temperatures, t and t + dt, and dE is the E. M. F. of the circuit, then the differential coefficient dE/dt is called the thermo-electric power of the two metals for the temperature t.


Thermo-electric Series. The arrangement of possible thermoelectric elements, q. v., in a table in the order of their relative polarity. Bismuth and antimony form a couple in which when their junction is heated the bismuth acts as the positive or negatively charged element and antimony as the negative or positively charged. Between these two extremes according to Seebeck the series runs as follows:

Antimony, Silver, Copper, Arsenic, Gold, Platinum, Iron, Molybdenum, Palladium, Steel, Tin, Cobalt, Cadmium, Lead, Nickel, Tungsten, Mercury, Bismuth. Zinc, Manganese,

A differential temperature of 1 C. (1.8 F.) in a bismuth-antimony couple maintains a potential difference of 103 micro-volts.

Matthiessen gives a different series; it is arranged in two columns; the first column has positive coefficients annexed the second has negative. On subtracting the greater one from the lesser, which, if the two elements are in different columns, of course amounts to adding after changing the negative sign, the relative potential difference due to the combination is obtained. + - Bismuth 25 Gas Coke 0.1 Cobalt 9 Zinc 0.2 Potassium 5.5 Cadmium 0.3 Nickel 5 Strontium 2.0 Sodium 3. Arsenic 3.8 Lead 1.03 Iron 5.2 Tin 1 Red Phosphorous 9.6 Copper 1 Antimony 9.8 Silver 1 Tellurium 179.9 Platinum 0.7 Selenium 290

Thus the relative E. M. F. of a bismuth-nickel couple, as both are in the + column, would be 25 - 5 = 20; that of a cobalt-iron couple, one being in the + column the other in the - column, would be 9 + 5.2 = 14.2. Alloys are not always intermediate to their constituents, and small amounts of impurities affect the results largely. This may account for the discrepancies of different observers. Other compounds could be introduced into the series.

Artificial silver sulphide has been used by Becquerel in a thermo-electric battery.


Thermo-electric Thermometer. A species of differential thermometer. It consists of two thermo-electric junctions connected in opposition with a galvanometer in the circuit. Any inequality of temperature in the two ends or junctions produces a current shown by the galvanometer. It may be used to determine the temperature of a distant place, one of the junctions being located there and the other being under control of the operator. If the latter junction is heated until no current is produced its temperature is evidently equal to that of the distant couple or junction. The heating may be done with hot water or mercury, or other melted metal. The temperature of the water, or other substance, gives the temperature of the distant place.

Thermolysis. Decomposition by heat; dissociation. All compound bodies are decomposable by heat if it is intense enough. Hence at very elevated temperatures there can be no combustion.


Thermometer. An instrument for indicating the intensity of heat. Three scales of degrees of heat are used in practise, the Fahrenheit, Ramur, and Centigrade, each of which is described under its own title. (See Zero, Thermometric-Zero, Absolute.) The ordinary thermometer depends on the expansion of mercury; in some cases alcohol is used. Besides these the compound bar principle as used in the thermostat (see Thermostat, Electric) is employed.

Thermometer, Electric. (a) A thermometer whose indications are due to the change of resistance in conductors with change of temperature. Two exactly similar resistance coils maybe electrically balanced against each other. On exposing one to a source of heat, its resistance will change and it will disturb the balance. The balance is restored by heating the other coil in a vessel of water when the temperature of the water gives the temperature of both coils. The coils are enclosed in water-tight metallic cases.

Synonym—Electric Resistance Thermometer.

(b) A differential thermometer may be made by connecting with a pair of conductors, two thermo-electric couples in opposition to each other, and including a galvanometer in series. On heating the junction of one couple more than that of the other a current at once goes through the galvanometer.

(c) (See Thermometer, Kinnersley's.)




Thermometer, Kinnersley's. A thermo-electrometer. A large glass tube is mounted on a standard and communicates with a small tube parallel to it. Water is poured in so as to rise in the small tube. Two wires terminating in bulbs enter the large tube by its top and bottom. The upper wire can be adjusted by moving up and down through a stuffing box. On discharging a Leyden jar through the space between the knobs on the two wires the water for a moment rises in the small tube. There is little or no accuracy in the instrument. It is allied to the electric mortar (see Mortar, Electric) as a demonstrative apparatus.

Synonyms—Electric Thermometer—Thermo-electrometer.

Thermo-multiplier. A thermo-electric battery including a number of couples. The term is generally applied to a small battery with its similar junctions facing in one direction and used for repeating Melloni's experiments on radiant energy, or so-called radiant heat.


Thermophone. An apparatus for reproducing sounds telephonically by the agency of heat; a receiving telephone actuated by heat. Thus a wire may be attached to the centre of a diaphragm and kept in tension therefrom, and the transmitting telephone current may be caused to pass through it. The wire changes in temperature and consequently in length with the pulses of current going through it and vibrates the diaphragm, reproducing the sound. It is to be distinguished from the thermo-electric telephone which involves the action of potential difference produced by thermo-electric action.

Thermostat, Electric. A thermostat or apparatus, similar to a thermometer in some cases, for closing an electric circuit when heated. It is used in connection with automatic fire alarms to give warning of fire. For this use a temperature of 52 C. (125 F.) is an approved one for setting one at, to complete the circuit. It is also applied to regulation of temperature, as in incubators.

(a) One kind of thermostat consists of a compound bar wound into a spiral and fastened at one end, to which a terminal of a circuit is connected. The bar may be made of two strips of brass and iron riveted together, and wound into a spiral. When such a bar is submitted to changes of temperature it bends in different directions, because brass expands and contracts more under changes of temperature than does iron. A contact point, to which the other terminal is connected, is arranged to make contact with the spiral at any desired degree of temperature, thus closing an electric circuit and ringing a bell, opening or closing a damper, or doing anything else to notify an attendant or to directly change the temperature.

If the brass forms the outside of the spiral, increase of temperature makes the bending of the spiral bring the coils still closer. If the brass forms the inside, increase of temperature makes the spiral tend to become less close. As shown in the cut, the brass should lie along the inside of the spiral.

Sometimes a straight compound bar is used, one of whose ends is fastened and the other is free. As the temperature changes such a bar curves more or less, its free end moving to and fro. Two contact screws are provided, one on each side of its free end. If the temperature falls it makes contact with one of these; if the temperature rises, it makes contact with the other. Thus it may close one of two circuits, one for a fall and the other for a rise in temperature.

It is well to introduce a third bar between the brass and iron ones, made of some material of intermediate coefficient of expansion.

(b) Another kind of thermostat comprises a vessel of air or other gas, which, expanding by heat, actuates a piston or other device and closes an electric circuit. Synonym—Electro-pneumatic Thermostat.

(c) Another form utilizes the expansion of mercury. The mercury is made part of an open electric circuit. As it expands it comes in contact with the other terminal of the circuit, thus completing it, when the current gives an alarm or does as is provided for in the apparatus employed.

Thermostats may be worked on either open or closed circuits; normally the circuit may be open as described and may close on rise of temperature, or it may be normally closed and open as the temperature rises.



Thomson Effect. In an unequally heated conductor the differential heating is either increased as in iron, or diminished as in copper by a current. In lead the phenomenon does not occur. It is termed the Thomson effect. It is intimately related to the Peltier effect.

In a thermo-electric couple a heated junction is the source of electro-motive force, if heated more than other parts of the circuit. The current in a copper-iron junction flows from the copper to the iron across the heated junction. A hot section of an iron conductor next to a cold section of the same is a source of thermoelectricity, in the sense that the hot section is negative to the colder. A current passing from the hot to the cold iron travels against rising potentials, and cools the iron in the cooler parts. As it passes to the hotter parts it travels against falling potentials and hence heats the iron in these parts. In this way a current intensifies differential heating in an iron conductor.

In copper the reverse obtains. In it the thermo-electric relations of hot and cold copper are the reverse of those of iron, and a current tends to bring all parts of a differentially heated copper conductor to an identical temperature.

As a current travels in iron from hot to cold it absorbs heat; in copper traveling from cold to hot it absorbs heat.

The convection of heat by a current of electricity in unequally heated iron is negative, for it is opposed to that convection of heat which would be brought about by the flow of water through an unequally heated tube. In copper, on the other hand, the electric convection of heat is positive. (Daniell.)

The above effects of the electric current upon an unequally heated conductor are termed the Thomson effects. In iron, at low red heat, they are reversed and are probably again reversed at higher temperatures.


Three Wire System. A system of distribution of electric current for multiple arc or constant potential service. It is the invention of Thomas A. Edison.

It includes three main wires which start from the central station or generating plant, and ramify with corresponding reduction in size, everywhere through the district or building to be lighted. As ordinarily carried out when dynamos are used, the dynamos are arranged in groups of two. One lateral lead starts from the negative binding post of one dynamo. The positive terminal of this dynamo connects to the negative of the other. Between the two dynamos the central or neutral lead is connected. The other lateral lead starts from the positive binding post of the second dynamo.

The lamps or other appliances are calculated for the potential difference of a single dynamo. They are arranged between the neutral wire and the laterals, giving as even a disposition as possible to the two laterals.


If evenly arranged and all burning or using current, no current goes through the neutral wire. If all the lamps situated on one lateral are on open circuit all the current goes through the neutral wire. In other cases the neutral wire receives the excess of current only.

The advantages of the system are that it uses smaller wire than the two wire system for lamps of the same voltage. If lamps of double the voltage were used the two wire system would be most economical.


Four wire and five wire systems have been more or less used, based on identical considerations, and involving in each case the coupling of three or of four dynamos respectively, or else employing a dynamo with special armature connections to give the requisite three-fold or four-fold division of total potential. In the five wire system the total voltage is four times that of a single lamp, the lamps are arranged four in series across the leads and the central wire is the only one that can be considered a neutral wire. When lamps are burning entirely from three side-leads they constitute a sort of three wire system by themselves, and their central wire may for the time be a neutral wire.

In some of the three wire mains, especially in the larger sizes, the neutral wire is made of much smaller section than that of a lateral conductor, because in extensive districts it is practically impossible that the current should be concentrated in the neutral wire.

Throw. In a galvanometer the instantaneous deflection of the needle when the contact or closing of the circuit is instantaneous, or when the discharge is completed before the needle begins to move. The throw of the needle is the datum sought when the ballistic galvanometer is used.


Throw-back Indicator. A drop annunciator, whose shutter or drop is electrically replaced.

Thrust-bearings. Bearings to support the end-thrust or push of a shaft. In disc armatures where the field-magnets attract the armatures in the direction of their axis of rotation, thrust-bearings have to be provided. In ordinary cylinder or drum armatures end-thrust is not applied, as a little end motion to and fro is considered advantageous as causing more even wear of the commutator surface.

Thunder. The violent report which, as we hear it, succeeds the lightning flash in stormy weather. It is really produced simultaneously with the lightning and is supposed to arise from disturbance of the air by the discharge. The rolling noise has been attributed to successive reflections between clouds and earth, and to series of discharges reaching the ear from different distances and through air of varying density. The subject is obscure. By timing the interval from lightning flash to the report of the thunder an approximate estimate of the distance of the seat of discharge can be made. The first sound of the thunder should be timed. An almost concurrence of thunder and lightning indicates immediate proximity of the discharge.

[Transcriber's note: The speed of sound at sea level is about 5 seconds per mile.]

Ticker. A colloquial name for a stock or market report automatic printing telegraph, which prints its quotations and messages on a long tape.


Time Constant. (a) When current is first turned into a circuit of considerable self-induction it is resisted rather by the inductance than by the resistance. It is governed by the ratio of resistance and self-induction and this factor represents the time which it takes for the current to reach a definite fraction of its final strength. This fraction is (2.7183 - 1)/2.7183 or 0.63. 2.7183 is the base of the Napierian system of logarithms. Thus if in any circuit we divide the inductance in henries by the resistance in ohms, the ratio gives the time-constant of the circuit, or it expresses the time which it will take for the current to reach 0.63 of its final value.

(b) In a static condenser the time required for the charge to fall to 1/2.7183th part of its original value.

Time Cut-outs. Cut-outs which automatically cut storage batteries out of the charging circuit when they are sufficiently charged.

Time-fall. In a secondary battery the decrease with use of electromotive force maintained by a primary or secondary battery. As the battery becomes spent its voltage falls. The conditions of the fall are represented by its discharging curve. (See Curve, Discharging.)

Time-reaction. A term in electro-therapeutics; the period of time occupied in the passage of the effects of an electric current from nerve to muscle.

Time-rise. In a secondary battery the increase of electromotive force produced during the charging process. Its rate and conditions are graphically shown in the charging curve. (See Curve, Charging.)

Tin. A metal; one of the elements; symbol, Sn; atomic weight, 117.8; equivalent, 58.9 and 29.5; valency, 2 and 4; specific gravity, 7.3. It is a conductor of electricity.

Relative resistance, compressed, (Silver = 1) 8.784 Specific resistance at 0 C. (32 F.), 13.21 microhms. Resistance of a wire at 0 C. (32 F.), (a) 1 foot long, weighing 1 grain, 1.380 ohms. (b) 1 foot long, 1/1000 inch thick, 79.47 " (c) 1 meter long, weighing 1 gram, .9632 " (d) 1 meter long, 1 millimeter thick, .1682 " Resistance of a 1 inch cube at 0 C. (32 F.), 5.202 microhms. Percentage of variation in resistance per degree C. (1.8 F.), at about 20 C. (68 F.), .0365 Electro-chemical equivalent (hydrogen = .0105), .619 mgs. .310 "


Tinnitus, Telephone. A nervous affection of the ear, of the order of professional cramp; it is attributed to too much use of the telephone.

Tin Sounders. A recent addition to the single needle telegraph. (See Telegraph, Single Needle.) It consists of small tin plates, cut and bent, and so fitted in pairs to the instrument, that the needle as deflected strikes one or the other on its right and left hand movements. The sounders can be made to give sufficiently distinctive sounds to make sound-reading, q. v., possible. Commercial tin plate, which is really tinned iron, seems to give the best results.


Tissandier's Solution. A solution for bichromate batteries. It is composed as follows: Water, 100 parts by weight potassium bichromate, 16 parts 66 sulphuric acid, 37 parts.

Tongue of Polarized Relay. The German silver extension of the vibrating or oscillating member of a polarized relay, corresponding to the armature of an ordinary relay.

Tongue of Polarized Relay, Bias of. In a Siemens' polarized relay the pole pieces are adjustable so that they may be brought nearer to or withdrawn from the tongue. One of the poles is adjusted so as to be nearer the tongue. This one-sided adjustment is the bias. Its effect is that when the relay is unexcited this pole attracts the armature so that it normally is drawn towards it. This ensures the normal contact of the tongue either with the contact point, or with the insulated stop piece or adjustment screw. Without bias the armature remains in contact with or drawn towards whichever pole it was last attracted to. In its usual use a bias is given it.

Top, Magnetic. A toy illustrating magnetic attraction. It consists of a disc or body of lead or other material, through which a magnetized steel spindle pointed at its lower end is thrust. A number of short pieces of iron wire are used with it. It is spun like an ordinary top upon the point of the spindle and one of the pieces of iron wire is laid by the side of its point. As it turns the magnetic adherence causes the piece of wire to be carried along in one direction by the rotation of the spindle, until the end is reached, when it goes over to the other side of the spindle and travels back again.

By using bent pieces of wire of various shapes the most curious effects are produced. Circles and S shaped pieces give good effects. To increase the mysterious effect covered iron wire (bonnet wire) may be employed.



Torpedo, Electric. (a) A fish, the Raia Torpedo, which possesses the power of giving electric shocks. (See Ray, Electric.)

(b) An instrument of war; a torpedo whose operations include electrical discharge or other electric function or factor of operation.

Torpedo, Sims-Edison. A torpedo driven by an electric motor, and also steered by electricity. Its motions are all controlled from the shore. The torpedo proper is carried some distance below the surface of the water by a vessel immediately above it, from which it is suspended by two rigid bars. In the torpedo is a cable reel on which the conducting cable is disposed. An electric motor and controlling gear are also contained within the torpedo. In its front the explosive is placed. It is driven by a screw propeller actuated by the electric motor. As it moves it pays out cable so that it has no cable to draw after it through the water, the cable lying stationary in the water behind it. This avoids frictional resistance to its motion. The maintenance of the torpedo at a proper depth is one of the advantages of the system.

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