Training Guide in Surface Weather Observations - Multiple Choices

2. If the hygrothermometer is not working, or either the dry-bulb or dew-point temperature is
outside the operating limits of the system, use the psychrometer to determine the missing data.
Always use the hygrothermometer dry-bulb temperature, if within limits, even though the dew
point temperature is determined by means of a psychrometer.
3. Record the temperature in column 11 and the dew point in column 12 of MF1M-10.
6.7 Liquid-In-Glass Minimum and Maximum Thermometers
6.7.1 Minimum Thermometer - How It Works
The minimum thermometer (see Figure 6-5) has an alcohol-filled bulb, graduated at 1° intervals. It is
exposed in a slightly lower than horizontal position. The alcohol is often colored to make it easier to
read. The bore contains a dark dumbbell-shaped object called an index. As the temperature rises, the
alcohol expands and flows around the index without displacing it. As the temperature falls the alcohol
column retreats until the top of the column just touches the index; with further cooling, the retreating
column moves the index nearer the bulb. As the temperature rises again, the alcohol column moves
toward the right without moving the index.
6.7.2 Maximum Thermometer - How It Works
The maximum thermometer (see Figure 6-5) has a mercury-filled bulb (sensing element). It is exposed
in a nearly horizontal position. Graduations at 1° intervals are etched on the stem. The bore is
constricted between the graduated portion of the stem and the bulb. As the temperature rises, some of
the expanding mercury in the bulb is forced to pass through the constricted portion into the graduated
portion. When the thermometer is lowered for reading, the top of the mercury column indicates the
highest temperature reached.
Figure 6-5. Maximum and Minimum Thermometers.
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