Equipment list 1 psychrometer 1 humidity table cloth covers for the wet bulb 1400 ml beaker 1 thermometer 1 styrofoam cup 1 plastic pitcher water ice l. introduction the relative humidity and dew point are critical values in understanding weather. in this laboratory exercise, you will measure the relative humidity and dew point, both indoors and outdoors. you will also compare your results with weather station values. il. theory humidity is the amount of water vapor in the air. saturated air is air that is filled to capacity with water vapor the capacity air has to hold water vapor is temperature dependent . o warm air has a much greater capacity than cold air water vapor adds pressure (called vapor pressure) to the air the most common way to report the amount of humidity in the air is to use relative humidity. the relative humidity is the ratio of the air's actual water vapor content compared with the amount of water vapor required for saturation a given temperature. the relative humidity: . is expressed as a percent . for saturated air content equals capacity has a 100 percent relative humidity o o can be changed in two ways add or subtract moisture to the air changing the air temperature o o the dew point temperature: the temperature the air needs to be cooled to reach saturation. cooling the air below the dew point causes condensation (e g. dew, fog, or cloud formation) 1