atmospheric pressure

atmospheric pressure
    n 1: the pressure exerted by the atmosphere [syn: {atmospheric
         pressure}, {air pressure}, {pressure}]
    

Pressure \Pres"sure\ (?; 138), n. [OF., fr. L. pressura, fr.
   premere. See 4th {Press}.]
   1. The act of pressing, or the condition of being pressed;
      compression; a squeezing; a crushing; as, a pressure of
      the hand.
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   2. A contrasting force or impulse of any kind; as, the
      pressure of poverty; the pressure of taxes; the pressure
      of motives on the mind; the pressure of civilization.
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            Where the pressure of danger was not felt.
                                                  --Macaulay.
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   3. Affliction; distress; grievance.
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            My people's pressures are grievous.   --Eikon
                                                  Basilike.
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            In the midst of his great troubles and pressures.
                                                  --Atterbury.
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   4. Urgency; as, the pressure of business.
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   5. Impression; stamp; character impressed.
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            All saws of books, all forms, all pressures past.
                                                  --Shak.
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   6. (Mech.) The action of a force against some obstacle or
      opposing force; a force in the nature of a thrust,
      distributed over a surface, often estimated with reference
      to the amount upon a unit's area.
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   7. Electro-motive force.
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   {Atmospheric pressure}, {Center of pressure}, etc. See under
      {Atmospheric}, {Center}, etc.

   {Back pressure} (Steam engine), pressure which resists the
      motion of the piston, as the pressure of exhaust steam
      which does not find free outlet.

   {Fluid pressure}, pressure like that exerted by a fluid. It
      is a thrust which is normal and equally intense in all
      directions around a point. --Rankine.

   {Pressure gauge}, a gauge for indicating fluid pressure; a
      manometer.
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Atmospheric \At`mos*pher"ic\, Atmospherical \At`mos*pher"ic*al\,
   a. [Cf. F. atmosph['e]rique.]
   1. Of or pertaining to the atmosphere; of the nature of, or
      resembling, the atmosphere; as, atmospheric air; the
      atmospheric envelope of the earth.
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   2. Existing or occurring in the atmosphere.
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            The lower atmospheric current.        --Darwin.
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   3. Caused, or operated on, by the atmosphere; as, an
      atmospheric effect; an atmospheric engine.
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   4. Dependent on the atmosphere. [R.]
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            In am so atmospherical a creature.    --Pope.
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   {Atmospheric engine}, a steam engine whose piston descends by
      the pressure of the atmosphere, when the steam which
      raised it is condensed within the cylinder. --Tomlinson.

   {Atmospheric line} (Steam Engin.), the equilibrium line of an
      indicator card. Steam is expanded "down to the atmosphere"
      when its pressure is equal to that of the atmosphere. (See
      {Indicator card}.)

   {Atmospheric pressure}, the pressure exerted by the
      atmosphere, not merely downwards, but in every direction.
      In amounts to about 14.7 Ibs. on each square inch.

   {Atmospheric railway}, one in which pneumatic power, obtained
      from compressed air or the creation of a vacuum, is the
      propelling force.

   {Atmospheric tides}. See under {Tide}.
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