Pontoon \Pon*toon"\, n. [F. ponton (cf. It. pontone), from L.
   ponto, -onis, fr. pons, pontis, a bridge, perhaps originally,
   a way, path: cf. Gr. ? path, Skr. path, pathi, panthan. Cf.
   {Punt} a boat.]
   1. (Mil.) A wooden flat-bottomed boat, a metallic cylinder,
      or a frame covered with canvas, India rubber, etc.,
      forming a portable float, used in building bridges quickly
      for the passage of troops.
      
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   2. (Naut.) A low, flat vessel, resembling a barge, furnished
      with cranes, capstans, and other machinery, used in
      careening ships, raising weights, drawing piles, etc.,
      chiefly in the Mediterranean; a lighter.
      
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   {Pontoon bridge}, a bridge formed with pontoons.

   {Pontoon train}, the carriages of the pontoons, and the
      materials they carry for making a pontoon bridge.
      
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   Note: The French spelling ponton often appears in scientific
         works, but pontoon is more common form.
         
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Bridge \Bridge\ (br[i^]j), n. [OE. brig, brigge, brug, brugge,
   AS. brycg, bricg; akin to Fries. bregge, D. brug, OHG.
   brucca, G. br["u]cke, Icel. bryggja pier, bridge, Sw. brygga,
   Dan. brygge, and prob. Icel. br[=u] bridge, Sw. & Dan. bro
   bridge, pavement, and possibly to E. brow.]
   1. A structure, usually of wood, stone, brick, or iron,
      erected over a river or other water course, or over a
      chasm, railroad, etc., to make a passageway from one bank
      to the other.
      
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   2. Anything supported at the ends, which serves to keep some
      other thing from resting upon the object spanned, as in
      engraving, watchmaking, etc., or which forms a platform or
      staging over which something passes or is conveyed.
      
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   3. (Mus.) The small arch or bar at right angles to the
      strings of a violin, guitar, etc., serving of raise them
      and transmit their vibrations to the body of the
      instrument.
      
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   4. (Elec.) A device to measure the resistance of a wire or
      other conductor forming part of an electric circuit.
      
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   5. A low wall or vertical partition in the fire chamber of a
      furnace, for deflecting flame, etc.; -- usually called a
      {bridge wall}.
      
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   {Aqueduct bridge}. See {Aqueduct}.

   {Asses bridge}, {Bascule bridge}, {Bateau bridge}. See under
      {Ass}, {Bascule}, {Bateau}.

   {Bridge of a steamer} (Naut.), a narrow platform across the
      deck, above the rail, for the convenience of the officer
      in charge of the ship; in paddlewheel vessels it connects
      the paddle boxes.

   {Bridge of the nose}, the upper, bony part of the nose.

   {Cantalever bridge}. See under {Cantalever}.

   {Draw bridge}. See {Drawbridge}.

   {Flying bridge}, a temporary bridge suspended or floating, as
      for the passage of armies; also, a floating structure
      connected by a cable with an anchor or pier up stream, and
      made to pass from bank to bank by the action of the
      current or other means.

   {Girder bridge} or {Truss bridge}, a bridge formed by
      girders, or by trusses resting upon abutments or piers.

   {Lattice bridge}, a bridge formed by lattice girders.

   {Pontoon bridge}, {Ponton bridge}. See under {Pontoon}.

   {Skew bridge}, a bridge built obliquely from bank to bank, as
      sometimes required in railway engineering.

   {Suspension bridge}. See under {Suspension}.

   {Trestle bridge}, a bridge formed of a series of short,
      simple girders resting on trestles.

   {Tubular bridge}, a bridge in the form of a hollow trunk or
      rectangular tube, with cellular walls made of iron plates
      riveted together, as the Britannia bridge over the Menai
      Strait, and the Victoria bridge at Montreal.

   {Wheatstones bridge} (Elec.), a device for the measurement
      of resistances, so called because the balance between the
      resistances to be measured is indicated by the absence of
      a current in a certain wire forming a bridge or connection
      between two points of the apparatus; -- invented by Sir
      Charles Wheatstone.
      
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