c. Dry Bulb Thermometer. The dry bulb thermometer is a standard
thermometer with the bulb shaded, but still left exposed to the wind.
d. Wet Bulb Thermometer. The wet bulb thermometer is a standard laboratory
glass thermometer with its bulb cover with a wick (heavy white corset or shoestring).
The wick dips into a flask or bottle of clean, preferably distilled, water.
The mouth of the flask or bottle should be about three-fourths of an inch
below the tip of the thermometer bulb.
The water level in the flask should be high enough to ensure thorough
wetting of the wick.
The water should be changed at least daily after rinsing out the flask and
washing the wick with soap and water.
To avoid erroneous readings, the water and wick must be free of all salts
e. Globe-Thermometer Apparatus. The globe-thermometer apparatus
consists of a 6-inch hollow copper sphere painted flat black on the outside and
containing a thermometer with its bulb at the center of the sphere.
The thermometer stem protrudes to the outside through a rubber stopper
tightly fitting into a brass tube soldered to the sphere.
The sphere usually has two small holes near the top used for suspending
the sphere with wire or strong cords.
The globe must be kept dull black at all times.
Keep the globe free of dust or rain streaks by dusting, washing, or
repainting as necessary.
f. Methods to Set Up a WBGT Apparatus. There are several methods for
setting up a WBGT apparatus. Figure 4-1 shows one such method.