counter-electro-motive force of the transformer falls and more currentpasses through the primary.Fig. 339. FERRANTI'S TRANSFORMER.The economy of the apparatus is in the fact that counter-electromotiveforce reduces current through a conductor without absorbing any energy.A resistance coil cuts down a current, but absorbs energy equal to thecurrent multiplied by the potential difference between the terminals ofthe coil. This electric energy is converted into heat energy and iswasted. But the counter-electromotive force of a transformer is exertedto reduce current without production of heat and with little waste ofenergy. This is one of the advantages of the alternating current systemof distribution of electric energy.The object of a transformer being to secure safety to the person or tolife by the separation of the high potential primary or street circuit,and the low potential house circuit, any contact of the two circuits inthe converter is a source of danger. Special care should be taken toensure absence of leakage, as it is termed. Mica or other insulation issometimes employed to prevent the wires from coming in contact bypiercing or sparking with the core and with each other.547 STANDARD ELECTRICAL DICTIONARY.Transformer, Commuting.A type of continuous current transformer, resembling a dynamo witharmature and field both stationary, but with revolving commutator, bywhich the magnetic polarity of a double wound armature is made torotate. This secures the desired action, of a change or lowering ofpotential.Transformer, Continuous Alternating.An apparatus for transforming a continuous into an alternating currentor the reverse. The combination of a continuous current dynamo with analternating current one is sometimes employed. It is a form of motordynamo.Another type is a regular dynamo with ordinary commutator and with, inaddition thereto, two, three or four contact rings, connecting to asmany symmetrically disposed points in the winding of the armature. Thiswill give out or receive alternating currents of two, three or fourphases according to the number of collecting rings. One winding servesfor both alternating and continuous currents.Transformer, Continuous Current.A machine of the dynamo type for changing the potential of a circuit. Inone form two armatures are mounted on one shaft in a single field or inseparate fields; one is a motor armature driven by the original current;the other generates the new current. This is a motor dynamo. In 1874Gramme constructed a machine with ring armature with two windings, ofcoarse and fine wire respectively, and with independent commutators.Such dynamo could transform currents up or down.Continuous current transformers have attained an efficiency of 83 percent. at full load, and of 75 per cent. at half load. Owing to thebalancing of the self-inductions of the two windings these machines donot spark. As the driven and driving parts are contained in one rotatingpart their friction is very slight.Transformer, Core.A transformer wound upon an enclosed core, such as the hedgehogtransformer (see Transformer, Hedgehog), or common induction coil.548 STANDARD ELECTRICAL DICTIONARY.Transformer, Hedgehog.An induction coil transformer whose iron core is composed of a bundle ofiron wires, which after the wire windings are in place have their endsspread out to reduce to some extent the reluctance of the circuit, whichat the best is high, as the air acts as the return circuit.This transformer has a low degree of hysteresis; and its efficiency forvery small loads or for no load is superior to that of the closedmagnetic circuit transformer.Fig. 340. SWINBURNE'S HEDGEHOG TRANSFORMER.Transformer, Multiple.A transformer connected in parallel with others between the two leads ofthe primary circuit. The term refers to the connection only and not toany peculiarity of the transformer itself.Transformer, Oil.A transformer with oil insulation. The advantage of this insulation isthat if pierced it at once closes, so that no permanent injury ensues.It is a self-healing form of insulation.Transformer, Series.Transformers connected in series upon the primary circuits. The term,like "multiple transformers," only applies to the connection, not to thetransformer. Series transformers are but little used.Transformer, Shell.A transformer with its iron core entirely outside of and enclosing theprimary and secondary winding. It may be made by the use of outer ironwire windings as core.Transformer, Welding.The transformer used for electric welding. (See Welding, Electric.) Itis a transformer with very long primary and exceedingly short and thicksecondary. It is used with the alternating current in the primary, andproduces in the secondary circuit which includes the bars to be welded avery low potential difference.Owing to the very low resistance of the secondary circuit this lowelectro-motive force produces a very strong current, which develops therequisite heat. The same type of transformer is used for brazing andsimilar purposes.549 STANDARD ELECTRICAL DICTIONARY.Transmitter.In general electric phraseology, any instrument which produces signalsto be transmitted through a line or circuit is a transmitter. Thus theMorse key in telegraphy or the Blake transmitter in telephony areexamples of such.Transmitter, Carbon.A form of microphone used as a telephone transmitter. (See CarbonTelephone.)Transposing.A method of laying metallic circuits for telephoning. The wires at shortintervals are crossed so that alternate sections lie on opposite sidesof each other. It is done to avoid induction.Transverse Electro-motive Force.Electro-motive force in a substance in which electric displacement istaking place, produced by a magnetic field. It is sometimes assigned asthe cause of the Hall effect, q. v.Trimmer, Brush.A shears for cutting off evenly and squarely the ends of copper dynamobrushes. The brushes when uneven from wear are removed from the brushholders, and their ends are sheared off in the trimmer.Trolley.A grooved metallic pulley or set of pulleys which runs along an activewire of a circuit, a lead from which trolley goes to earth or connectswith another wire, so that the trolley takes current generally foroperating a street car motor placed upon the circuit leading from it; arolling contact with an electric lead.Trolleys are principally used on electric railroads, and are nowuniversally of the sub-wire system, being at the end of a pole which isinclined backward and forced upward by springs, so as to press thetrolley against the bottom of the wire. Thus the trolley does notincrease the sagging of the wire, but tends to push it up a little inits passage.Trolley, Double.A trolley with two rollers or grooved wheels, placed side by side, andrunning on two parallel leads of wire. It is adapted to systemsemploying through metallic trolley lines with the motors in multiplearc, connecting or across the two leads.Trolley Section.An unbroken or continuous section of trolley wire.Trouvé's Solution.An acid exciting and depolarizing solution for a zinc-carbon battery.Its formula is as follows: Water, 80 parts; pulverized potassiumbichromate, 12 parts; concentrated sulphuric acid, 36 parts; all partsby weight. The pulverized potassium bichromate is added to the water,and the acid is added slowly with constant stirring. As much as 25 partspotassium bichromate may be added to 100 parts of water. The heatingproduced by the acid and water dissolves nearly all the potassium salt.Use cold.550 STANDARD ELECTRICAL DICTIONARY.True Contact Force.A species of electro-motive force whose existence is supposed to beproved by the Peltier effect. The lowering in temperature of a contactof dissimilar metals is attributed to a force that helps the current onits way if in the direction of thermo-current proper to the junction andopposing it if in the reverse. The true contact force is taken toexplain this phenomenon; thermo-electric force cannot, as there is noheat or cold applied to the junction.Trumpet, Electric.An apparatus consisting of a vibrating tongue, kept in motion byelectricity as in the buzzer, q. v., placed in the small end of atrumpet-shaped tube.Trunking Switchboard.A telephone switchboard arranged in sections, which sections areconnected by trunk lines, through which trunk lines the desiredconnectionsare made.Trunk Lines.In telephone distribution systems, the lines connecting differentstations, or different sections of a switch-board and used by anyonerequiring such connections; one trunk line answers for a number ofsubscribers.Tube, Electric.A tube of glass around which is pasted a series of tinfoil circles,diamonds, or little squares, or other form of interrupted conductor. Thepieces generally are placed in the line of a spiral. When a staticdischarge of electricity takes place along the conductor a row of brightsparks is produced at the breaks in the conductor. These by reflectionare multiplied apparently, and a beautiful effect of intersecting orcrossing spirals of sparks is presented.The experiment is in line with the luminous pane and lightning jar, andis used merely as a demonstration, or lecture experiment.Synonym--Luminous Tube.Tubular Braid.A braid woven of tissue or worsted, and tubular or hollow. Its object isto provide a covering which can be drawn over joints in covered wires.In making the joint the ends of the wires are necessarily bared, and ashort piece of tubular braid is used for covering them. It is drawn byhand over the joint.Turns.An expression applied to the convolutions of wire in a solenoid,electro-magnet, or other apparatus or construction of that kind. A turnindicates a complete encircling of the core or axis of the object. Thusa wire wound five times around a bar gives five turns.While this is its primary meaning the term if compounded may refer tovirtual turns. Thus an ampere-turn means one ampere passing through oneturn. But ten ampere-turns may mean ten amperes passing through tenturns, five amperes passing through two turns, and so on. This use isanalogous to a dimension of length in a compound word, as foot-pound.[Transcriber's note: "But ten ampere-turns may mean ten amperes passingthrough ONE turn or one ampere through ten turns, and so on."]There may be a number of kinds of turns qualified by descriptiveadjectives, as series-turns, the turns of wire in a series circuit of acompound dynamo. In the same way there are shunt-turns. If seriesampere-turns or shunt ampere-turns are meant the word ampere should beincluded.551 STANDARD ELECTRICAL DICTIONARY.Turns, Dead, of a Dynamo.The rotations of a dynamo armature while it is building itself up orexciting itself. The expression is a bad one, as it is likely to beconfounded with the dead turns of armature wire.Turns, Primary Ampere-.The ampere-turns in a primary circuit of an induction coil ortransformer. In an electric welding transformer, or in the transformerused in the alternating current system, where efficiency is an importantelement, the ampere-turns in primary and secondary for an efficiency of100 per cent. should be equal. In the case of an experimental inductioncoil other considerations outweigh that of mere efficiency. Insulation,including security from piercing, and the production of as long a sparkas possible, are, in these cases, the controlling consideration.[Transcriber's note: A 100 per cent efficient transformer is impossible,but over 99 per cent is common. At room temperature there is always somelost flux, eddy currents and resistive losses.]Turns, Secondary Ampere-.The ampere-turns on the secondary circuit of an induction coil ortransformer. These depend on the path provided for the current. If ofnegligible inductance, such as a number of incandescent lamps wouldprovide, the ampere-turns should be equal to those of the primary coil.(See Turns, Primary Ampere.)Typewriter, Electric.A typewriter in which the work of printing or of pressing the type facesagainst the paper, or printing ribbon, is done by electro-magneticattraction. The keys close electric circuits, throwing theelectro-magnetic action into play. This involves the use of electricityfor what is ordinarily only a mechanical process. The strength of theimpression, however, is independent of the touch of the operator. It hasnot come into very extensive use.[Transcriber's note: IBM introduced widely used electric typewriters in1935.]