The temperature of the air is measured with a thermometer in units called degrees. These instruments should be housed outdoors in a shelter where it is not exposed to direct sunlight, or precipitation. (See Appendix for directions on how to make the shelter). Thermometers are fairly inexpensive instruments, and I strongly recommend purchasing one for your weather station since you have to make the shelter for the instrument.
Meteorologists use a set of two thermometers to record minimum/maximum readings because it is important for them to obtain the warmest and coldest temperature daily. Realistically, the thermometers are one-way thermometers that have to be reset each day. The minimum thermometer uses alcohol as a liquid, with a small indicator inside the tube. The alcohol retracts and pulls the indicator along with it as the air cools, thus leaving the indicator at the lowest temperature of the day.
The maximum thermometer uses mercury. Mercury is stored in the “neck down” portion the tube. Mercury is a thicker liquid than alcohol. As the temperature increases, the mercury expands beyond the constriction into the top part of the instrument where it stays in place recording the maximum temperature of the day.
As far as the classroom weather station is concerned, a standard air thermometer can be used. These thermometers break easily and should be handled carefully. Tthey should also be cleaned daily of outside elements such as dust, dirt and moisture so that the most accurate temperatures are recorded. In order to get the minimum and maximum temperature for each day, a student should record the temperature early in the morning and at the end of the school day.