Glue the two thermometers side by side on a vertical surface, making sure they are level with each other and not tilted. The thermometers have to be identical in order that readings taken can be accurate.
Soak the shoelace in a small pot of water, then tie one end around the bulb section of one of the thermometers. This thermometer becomes the wet bulb while the other is referred to as the dry bulb. Place the pot of water below the wet bulb thermometer with the rest of the shoelace left submerged, but don't let the water itself touch the bulb.
Give the thermometers an hour or so to set up and reach readable temperatures. The dry bulb thermometer measures the air temperature while the wet bulb measures the temperature based on how fast moisture evaporates into the air. In humid conditions, the moisture from the shoelace does not evaporate much, so the temperatures in both thermometers stay almost the same. In dry conditions, the wet bulb thermometer reads a noticeably lower temperature.
Heat the sewing needle over a flame and use it to melt a hole through the center of the straight edge of the protractor and through the ping-pong ball. Make sure the sewing needle is long enough to go all the way through the ping-pong ball so the holes line up.
Thread one end of the fishing line through the melted hole in the protractor and tie it off with a tight knot. Then thread the line through the ping-pong ball, making sure it goes right through and that it is also tied off to hold it in place. Hold the protractor up with the curved edge facing down. Keep it as straight as possible so that the fishing line transects the center of the protractor's curve.
Take the instrument outside and point it in the direction of the wind. Don't stand directly behind the protractor as this may cause wind turbulence. The wind will blow the ping-pong ball back with the angle at which the fishing line lays on the protractor curve, indicating the wind speed. The more degrees the wire moves, the stronger the wind speed.