Source : Webster's Revised Unabridged Dictionary (1913)

Thermometer \Ther*mom"e*ter\, n. [Thermo- + -meter: cf. F.
   thermom[`e]tre. See {Thermal}.] (Physics)
   An instrument for measuring temperature, founded on the
   principle that changes of temperature in bodies are
   accompained by proportional changes in their volumes or
   dimensions.

   Note: The thermometer usually consists of a glass tube of
         capillary bore, terminating in a bulb, and containing
         mercury or alcohol, which expanding or contracting
         according to the temperature to which it is exposed,
         indicates the degree of heat or cold by the amount of
         space occupied, as shown by the position of the top of
         the liquid column on a graduated scale. See
         {Centigrade}, {Fahrenheit}, and {R['e]aumur}. To reduce
         degrees Fahrenheit to degrees Centigrade, substract
         32[deg] and multiply by 5/9; to reduce degrees
         Centigrade to degrees Fahrenheit, multiply by 9/5 and
         add 32[deg].

   {Air thermometer}, {Balance thermometer}, etc. See under
      {Air}, {Balance}, etc.

   {Metallic thermometer}, a form of thermometer indicating
      changes of temperature by the expansion or contraction of
      rods or strips of metal.

   {Register thermometer}, or {Self-registering thermometer}, a
      thermometer that registers the maximum and minimum of
      temperature occurring in the interval of time between two
      consecutive settings of the instrument. A common form
      contains a bit of steel wire to be pushed before the
      column and left at the point of maximum temperature, or a
      slide of enamel, which is drawn back by the liquid, and
      left within it at the point of minimum temperature.



   14. (Paint.)
       (a) The representation or reproduction of the effect of
           the atmospheric medium through which every object in
           nature is viewed. --New Am. Cyc.
       (b) Carriage; attitude; action; movement; as, the head of
           that portrait has a good air. --Fairholt.

   15. (Man.) The artificial motion or carriage of a horse.

   Note: Air is much used adjectively or as the first part of a
         compound term. In most cases it might be written
         indifferently, as a separate limiting word, or as the
         first element of the compound term, with or without the
         hyphen; as, air bladder, air-bladder, or airbladder;
         air cell, air-cell, or aircell; air-pump, or airpump.

   {Air balloon}. See {Balloon}.

   {Air bath}.
       (a) An apparatus for the application of air to the body.
       (b) An arrangement for drying substances in air of any
           desired temperature.

   {Air castle}. See {Castle in the air}, under {Castle}.

   {Air compressor}, a machine for compressing air to be used as
      a motive power.

   {Air crossing}, a passage for air in a mine.

   {Air cushion}, an air-tight cushion which can be inflated;
      also, a device for arresting motion without shock by
      confined air.

   {Air fountain}, a contrivance for producing a jet of water by
      the force of compressed air.

   {Air furnace}, a furnace which depends on a natural draft and
      not on blast.

   {Air line}, a straight line; a bee line. Hence

   {Air-line}, adj.; as, air-line road.

   {Air lock} (Hydr. Engin.), an intermediate chamber between
      the outer air and the compressed-air chamber of a
      pneumatic caisson. --Knight.

   {Air port} (Nav.), a scuttle or porthole in a ship to admit
      air.

   {Air spring}, a spring in which the elasticity of air is
      utilized.

   {Air thermometer}, a form of thermometer in which the
      contraction and expansion of air is made to measure
      changes of temperature.

   {Air threads}, gossamer.

   {Air trap}, a contrivance for shutting off foul air or gas
      from drains, sewers, etc.; a stench trap.

   {Air trunk}, a pipe or shaft for conducting foul or heated
      air from a room.

   {Air valve}, a valve to regulate the admission or egress of
      air; esp. a valve which opens inwardly in a steam boiler
      and allows air to enter.

   {Air way}, a passage for a current of air; as the air way of
      an air pump; an air way in a mine.

   {In the air}.
       (a) Prevalent without traceable origin or authority, as
           rumors.
       (b) Not in a fixed or stable position; unsettled.
       (c) (Mil.) Unsupported and liable to be turned or taken
           in flank; as, the army had its wing in the air.

   {To take air}, to be divulged; to be made public.

   {To take the air}, to go abroad; to walk or ride out.

Source : WordNet®

air thermometer
     n : thermometer that measures temperature by changes in the
         pressure of a gas kept at constant volume [syn: {gas
         thermometer}]