How to Make a Wet Bulb Thermometer

Wet bulb thermometers are used to measure the amount of relative humidity in the air. This is important when determining whether it is safe to work outside, when growing types of plants that require a certain amount of humidity, when incubating and hatching eggs or when drying or curing certain crops.

Things You'll Need

• 1 dry bulb thermometer (mercury in glass is best)
• 6-inch-long piece of a hollow cotton shoelace
• 2-inch piece of dental floss
• Dish or other container of water

Instructions

Making the Wet Bulb Thermometer

1. 

   Cut the shoelace down so there is no plastic tip and the lace can be opened up into a narrow tube.

2. 

   Insert the bulb of the thermometer, end first, about 1 inch into the shoelace.

3. Using the dental floss, secure the shoelace to the thermometer just above the bulb, making sure all the numbers can still be read.

4. 

   Stick the opposite end of the shoelace into a container of water so that there are at least 3 inches of the shoelace in the water. This will serve as a wick to allow the water to reach the thermometer's bulb.

Tips & Warnings

• If you want to hang your thermometer, hang a shelf in a convenient location on your wall, fence or wherever you want to place your thermometer. Place the dish of water on the shelf, then insert the loose end of the shoelace. Hold the thermometer up and mark off where it needs to hang in order for the shoelace to reach well into the water. Pound in a nail, hang the thermometer and make sure the shoelace is in the water. Make sure you keep an adequate supply of water in your container, or the thermometer will no longer work as a wet bulb thermometer.

Resources

• Climate Glossary
• Measuring the Relative Humidity & Dew Point Temperature