T
Table-push. A push-button connected with a call-bell and fixed on a table for convenience in using.
Tamadine. A form of cellulose used for making the filaments of incandescent lamps. The material is cut into proper shapes, carbonized, and flashed.
Tangent Galvanometer. (See [Galvanometer, Tangent].)
Tape, Insulating. Prepared tape used in covering the bared ends of wires or joints.
Tap-wires. The conductors in trolley systems that at stated intervals, take the current from the mains and supply it to the bare feed-wires.
Telegraph. A system of electric communication invented by S. F. B. Morse, in which the dot-and-dash characters are used. There are various modifications of the system—double (or duplex), multiplex, and quadruplex—by means of which a number of messages may be sent out over the same wires at one time. Communication from place to place is had over wires mounted on poles, or by underground or submarine cables.
Telegraphy, Wireless. A system of telegraphy carried on without the aid of wires, using instead the ether waves of the atmosphere to conduct the vibrations overhead, and the ground, or earth, as a return. The present limit of its working is about four thousand miles.
Telephone. An instrument and apparatus for the transmission of articulate speech by the electric current. A magnet is encased in a tube and is encircled at one end by a coil of fine, insulated wire. A diaphragm of thin iron is fixed in front of the coil and close to the end of the magnet. The ends of the coil-wires are connected with a line, at the other end of which another and similar instrument is installed. The voice causes the sending diaphragm to vibrate, and these waves are transmitted to the other instrument, where they can be heard through contra-vibrations of the receiving diaphragm.
Telephone, Long-distance. A telephone of modern construction, in which the sound-recording mechanism is so sensitive as to make the vibrations of the voice audible at long distances. It will work satisfactorily at one thousand or even fifteen hundred miles.
Terminal. The end of any open electric circuit, or of any electric apparatus, as the electrodes of a battery.
Thermostat, Electric. An apparatus similar in some respects to a thermometer, and used for closing an electric circuit when the latter becomes heated. It is used in connection with automatic fire-alarms to give warning of fire. For this purpose the metal coil is arranged to close the contact at a temperature of 125° F. It usually consists of a compound strip of metal wound in the form of a spiral and fastened at one end. To this end one terminal of a circuit is connected. The expansion of the coil causes its loose end to touch a contact-point and close the circuit.
Third Rail. A railway motive system which employs a third rail instead of an overhead trolley feed-wire. The rail is laid on or under the surface of the ground and properly insulated. A shoe from the car bears on the rail and takes up the current.
Three-wire Circuit. A system invented by Edison for the distribution, from two dynamos, of current for multiple arc or constant potential service. One wire or lead starts from the positive pole of one dynamo, another from the negative pole of the other dynamo, and between the two dynamos the central or neutral lead is made fast.
Now the dynamos may generate a current of 220 volts, and send it, at this strength, through the outer wires; but if lamps are connected between either of the outer and the neutral wires, the current, passing through the lamps, will be reduced to 110 volts.
Time-ball, Electric. A ball which, by means of electricity, is made to drop from the top of a high pole, giving a visual signal for twelve o’clock or any other hour that may be designated.
Traction, Electric. The propulsion of a car or conveyance by means of electricity.
Transformer. In alternating-current systems, the induction-coil by means of which the primary current, with high initial electro-motive force, is changed into a secondary current with low initial electro-motive force.
Transmission. The conveyance of electric energy and currents from one point to another by the proper means of conduction.
Transmitter. An instrument which originates the signals which are sent through a line or circuit. The Morse key in telegraphy and the Blake transmitter in telephony are examples.
Tri-phase. Three-phase.
Trolley. A contact-wheel of bronze which rolls under the supply-wire in an overhead traction system and takes off the current necessary to run the car motors.
Trolley-wheel. The same as Trolley.
Trolley-wire. The overhead wire in a traction system which feeds the current through a trolley-wheel and pole to the motors of a car running underneath.
True Ohm. (See [Ohm, True].)
True Resistance. (See [Resistance, True].)
Two-wire Circuit. The single system universally used for light and power transmission of current.