the term "partial pressure"
meanings are the same.
(5) Now that we have defined the common terms associated with humidity,
let's see how temperature affects humidity. A cold room in a house usually feels
damp. However, if the same room is heated the dampness seems to disappear and the
room becomes dry.
The amount of moisture in the room has not been reduced by
However, the capacity of the air in the room for moisture
increases when the temperature is raised.
EXAMPLE: Suppose the air in a room at 32F. contains 2 grains of water vapor per
cubic foot. As shown in Table 8, the capacity of air at 32F. is 2.118 gr/ft3 or 94
When the temperature is raised to 68F., the
Such air will feel damp.
amount of moisture is unchanged, but the capacity of the air is now 7.56 gr/ft3
divided by 7.56 gr/ft3, or 26 percent. This air feels dry. We see that increasing
the temperature decreases the relative humidity.
On the other hand, if the
temperature is lowered, the relative humidity will increase.
Water vapor capacity of air
(c) Humidity Measurement Instruments.
Instruments that are used to
determine relative humidity are called either psychrometers or hygrometers.
Generally, the act and dry bulb instrument is called a psychrometer and direct
record relative humidity.