Tel·e·graph n.  An apparatus, or a process, for communicating intelligence rapidly between distant points, especially by means of preconcerted visible or audible signals representing words or ideas, or by means of words and signs, transmitted by electrical action.
 Note: ☞ The instruments used are classed as indicator, type-printing, symbol-printing, or chemical-printing telegraphs, according as the intelligence is given by the movements of a pointer or indicator, as in Cooke & Wheatstone's (the form commonly used in England), or by impressing, on a fillet of paper, letters from types, as in House's and Hughe's, or dots and marks from a sharp point moved by a magnet, as in Morse's, or symbols produced by electro-chemical action, as in Bain's. In the offices in the United States the recording instrument is now little used, the receiving operator reading by ear the combinations of long and short intervals of sound produced by the armature of an electro-magnet as it is put in motion by the opening and breaking of the circuit, which motion, in registering instruments, traces upon a ribbon of paper the lines and dots used to represent the letters of the alphabet. See Illustration in Appendix, and Morse code.
 Acoustic telegraph. See under Acoustic.
 Dial telegraph, a telegraph in which letters of the alphabet and numbers or other symbols are placed upon the border of a circular dial plate at each station, the apparatus being so arranged that the needle or index of the dial at the receiving station accurately copies the movements of that at the sending station.
 Electric telegraph, or Electro-magnetic telegraph, a telegraph in which an operator at one station causes words or signs to be made at another by means of a current of electricity, generated by a battery and transmitted over an intervening wire.
 Facsimile telegraph. See under Facsimile.
 Indicator telegraph. See under Indicator.
 Pan-telegraph, an electric telegraph by means of which a drawing or writing, as an autographic message, may be exactly reproduced at a distant station.
 Printing telegraph, an electric telegraph which automatically prints the message as it is received at a distant station, in letters, not signs.
 Signal telegraph, a telegraph in which preconcerted signals, made by a machine, or otherwise, at one station, are seen or heard and interpreted at another; a semaphore.
 Submarine telegraph cable, a telegraph cable laid under water to connect stations separated by a body of water.
 Telegraph cable, a telegraphic cable consisting of several conducting wires, inclosed by an insulating and protecting material, so as to bring the wires into compact compass for use on poles, or to form a strong cable impervious to water, to be laid under ground, as in a town or city, or under water, as in the ocean.


 In·di·ca·tor n.
 1. One who, or that which, shows or points out; as, a fare indicator in a street car.
 2. Mach. A pressure gauge; a water gauge, as for a steam boiler; an apparatus or instrument for showing the working of a machine or moving part; as: (a) Steam Engine An instrument which draws a diagram showing the varying pressure in the cylinder of an engine or pump at every point of the stroke. It consists of a small cylinder communicating with the engine cylinder and fitted with a piston which the varying pressure drives upward more or less against the resistance of a spring. A lever imparts motion to a pencil which traces the diagram on a card wrapped around a vertical drum which is turned back and forth by a string connected with the piston rod of the engine. See Indicator card (below). (b) A telltale connected with a hoisting machine, to show, at the surface, the position of the cage in the shaft of a mine, etc.
 3. Mech. The part of an instrument by which an effect is indicated, as an index or pointer.
 4. Zool. Any bird of the genus Indicator and allied genera. See Honey guide, under Honey.
 5. Chem. That which indicates the condition of acidity, alkalinity, or the deficiency, excess, or sufficiency of a standard reagent, by causing an appearance, disappearance, or change of color, as in titration or volumetric analysis.
 Note: ☞ The common indicators are litmus, tropæolin, phenol phthalein, potassic permanganate, etc.
 Indicator card, the figure drawn by an engine indicator, by means of which the working of the engine can be investigated and its power calculated. The Illustration shows one form of indicator card, from a steam engine, together with scales by which the pressure of the steam above or below that of the atmosphere, corresponding to any position of the engine piston in its stroke, can be measured. Called also indicator diagram.
 Indicator telegraph, a telegraph in which the signals are the deflections of a magnetic needle, as in the trans-Atlantic system.

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