Indicator \In"di*ca`tor\ ([i^]n"d[i^]*k[=a]`t[~e]r), n. [L.: cf.
F. indicateur.]
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1. One who, or that which, shows or points out; as, a fare
indicator in a street car.
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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.
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3. (Mech.) The part of an instrument by which an effect is
indicated, as an index or pointer.
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4. (Zool.) Any bird of the genus Indicator and allied
genera. See Honey guide, under Honey.
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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.
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Note: The common indicators are litmus, trop[ae]olin, phenol
phthalein, potassic permanganate, etc.
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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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Telegraph \Tel"e*graph\, n. [Gr. ? far, far off (cf. Lith. toli)
+ -graph: cf. F. t['e]l['e]graphe. See Graphic.]
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.
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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.
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Note: In 1837, Samuel F. B. Morse, an American artist,
devised a working electric telegraph, based on a rough
knowledge of electrical circuits, electromagnetic
induction coils, and a scheme to encode alphabetic
letters. He and his collaborators and backers
campaigned for years before persuading the federal
government to fund a demonstration. Finally, on May 24,
1844, they sent the first official long-distance
telegraphic message in Morse code, "What hath God
wrought," through a copper wire strung between
Washington, D.C., to Baltimore, Maryland. The phrase
was taken from the Bible, Numbers 23:23. It had been
suggested to Morse by Annie Ellworth, the young
daughter of a friend. --Library of Congress, American
Memories series
(http://memory.loc.gov/ammem/today/may24.html).
[PJC]
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.
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