The whirling psychrometer contains two mercury-in-glass thermometers with a scale of minus 5 to plus
50 degrees Celsius, in 0.5 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’.
- Fill the plastic, lidded water bottle at the end of the instrument with water and wait 5-10 minutes
for the cloth sleeve around the wet-bulb thermometer to become damp.
- Pull down the handle so it locks into place, and swing the instrument around above your head about
30 to 50 times.
- Record the wet-bulb and dry-bulb temperatures.
- Repeat the process and compare the temperature readings. Repeat until the readings are consistent.
- Calculate the wet-bulb depression - the dry-bulb temperature minus the wet-bulb temperature.
- Determine the relative humidity (%) using the table (section 3). Read down from the wet-bulb depression
and across from the dry-bulb temperature.
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