Source : Webster's Revised Unabridged Dictionary (1913)

   2. The condition of rarefaction, or reduction of pressure
      below that of the atmosphere, in a vessel, as the
      condenser of a steam engine, which is nearly exhausted of
      air or steam, etc.; as, a vacuum of 26 inches of mercury,
      or 13 pounds per square inch.

   {Vacuum brake}, a kind of continuous brake operated by
      exhausting the air from some appliance under each car, and
      so causing the pressure of the atmosphere to apply the
      brakes.

   {Vacuum pan} (Technol.), a kind of large closed metallic
      retort used in sugar making for boiling down sirup. It is
      so connected with an exhausting apparatus that a partial
      vacuum is formed within. This allows the evaporation and
      concentration to take place at a lower atmospheric
      pressure and hence also at a lower temperature, which
      largely obviates the danger of burning the sugar, and
      shortens the process.

   {Vacuum pump}. Same as {Pulsometer}, 1.

   {Vacuum tube} (Phys.), a glass tube provided with platinum
      electrodes and exhausted, for the passage of the
      electrical discharge; a Geissler tube.