You'll need:
An empty 2 liter plastic soft drink bottle, scissors, two
indoor/outdoor thermometers, 2 large rubber bands and a 6-inch
(15 centimeter) piece of a cotton shoe lace (the kind that's a
tube)
Steps:
1. Cut off the top half of the bottle. Cut a slot about two inches (5 centimeters) from the bottom on one side of the bottle. Stretch the two rubber bands around the bottle spacing them about two inches (5 centimeters) apart. And slide the thermometers under the rubber bands.
2. Position one thermometer next to the slot. Open one end of the shoelace and slip it over the bulb end of this thermometer. Slip the free end of the shoelace through the slot so it lays on the bottom of the bottle. Pour enough water into the bottle to fill it up just to below the slot. Add more water daily as needed to keep the bottle from going dry.
3. To find out what the humidity is outdoors, take the hygrometer outside. Wait at least fifteen minutes before reading both the dry bulb thermometer (one without the shoe lace) and the wet bulb thermometer.