How do you use hygrometers?

Answer 1

Fill the water bottle and screw it on to the instrument.

Then hang the hygrometer (by the loop at the top) on a

wall or a tree, for instance, for at least five to 10 minutes

before taking the measurements.

Ideally the instrument should be in a well-shaded spot

or in a Stevenson screen (refer to "Making your own

weather station" in Section 4: Contacts and further

information).

The instrument contains two alcohol-in-glass thermometers with a scale of minus 10 to plus 110 degrees

Celsius, in 1 degree increments. The

end of the 'wet-bulb' thermometer is

covered with a damp cloth dipped in

water. The other thermometer is the

'dry-bulb'.

6 Record the wet-bulb and dry-bulb

temperatures.

6 Calculate the wet-bulb depression

- the dry-bulb temperature minus

the wet-bulb temperature.

6 Determine the relative humidity

(%) using the table (reverse

page). Read down from the wetbulb depression and across from

the dry-bulb temperature.

do's and don'ts

Be careful with the instrument. The thermometers are

made of glass and can easily break.

Empty the water bottle before returning the

hygrometer to its box.

how it works

The hygrometer works on a similar principle to the whirling

psychrometer. The main difference is that the hygrometer

is not rotated, so evaporation from the damp cloth around

the wet-bulb thermometer occurs more slowly.