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How to Build a Psychrometer with Wood

A psychrometer lets you become your own personal weatherman -- to a degree. Using two thermometers, you can make a psychrometer at home to estimate the humidity of the air. Using this and other information, such as the barometric pressure in your area (which can be found on the National Weather Service website), you can predict the type of weather your area will experience for that day. Creating your homemade psychrometer takes only a few minutes and a few simple materials.

Things You'll Need

2-by-1-1/2-inch board
Clear tape
2 non-mercury thermometers
Gauze
Water

Instructions

- 1
  Tape each thermometer to the same end of the board; place the thermometers on opposite sides with their bulbs hanging over the edge of the board. The thermometers should be parallel to the board (not perpendicular).
- 2
  Wrap one of the thermometer bulbs in gauze. This becomes your "wet" thermometer. Dip it in a cup of clean water until the gauze is soaked.
- 3
  Cool down the wet thermometer with a fan or by moving it through the air; your goal is to get the wet thermometer reading to its coolest temperature. Once you've done this, subtract the wet thermometer reading from the dry thermometer and cross-reference this number using a relative humidity chart (in the Resources section) to find the relative humidity.
  
  For example, if your dry thermometer reads 20 C and your wet thermometer reads 18 C, according to the chart the relative humidity is 88%.

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