Q.
Does anybody have an easy explanation of the meaning of "wet bulb" and "dry bulb" as they pertain to temperature measurement and other readings?
A.
The dry-bulb is a thermometer that is dry. The D-B temperature is the temperature that you hear on the weather report or that you read on a thermostat in your house.
The wet-bulb is a regular thermometer with a wet (distilled water) muslin wick covering it, and brisk air flow across the wick (600 feet per minute). As a result of evaporative cooling, the W-B temperature will be cooler than the D-B temperature.
If you know the D-B and W-B temperatures, you can look up relative humidity (RH), equilibrium moisture content, dew point, etc. This relationship was established in about 1909 by the U.S. Weather Bureau -- I think the scientist's name was Marvin.
Gene Wengert, forum moderator
As Gene stated, the wet-bulb temperature will be lower than the dry-bulb temperature because of evaporative cooling (assuming less than 100% RH). The difference between the dry-bulb temp and the wet-bulb temp is known as the "depression." The larger the depression (larger difference between wet- and dry-bulb), the lower the RH.
